Adding upstream version 13.4.upstream/13.4upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

19 files changed, 4519 insertions, 0 deletions

diff --git a/src/backend/port/.gitignore b/src/backend/port/.gitignore
new file mode 100644
index 0000000..4ef36b8
--- /dev/null
+++ b/src/backend/port/.gitignore
@@ -0,0 +1,3 @@
+/pg_sema.c
+/pg_shmem.c
+/tas.s
diff --git a/src/backend/port/Makefile b/src/backend/port/Makefile
new file mode 100644
index 0000000..2d00b4f
--- /dev/null
+++ b/src/backend/port/Makefile
@@ -0,0 +1,48 @@
+#-------------------------------------------------------------------------
+#
+# Makefile--
+#    Makefile for the port-specific subsystem of the backend
+#
+# We have two different modes of operation: 1) put stuff specific to Port X
+# in subdirectory X and have that subdirectory's make file make it all, and
+# 2) use conditional statements in the present make file to include what's
+# necessary for a specific port in our own output.  (1) came first, but (2)
+# is superior for many things, like when the same thing needs to be done for
+# multiple ports and you don't want to duplicate files in multiple
+# subdirectories.  Much of the stuff done via Method 1 today should probably
+# be converted to Method 2.
+#
+# IDENTIFICATION
+#    src/backend/port/Makefile
+#
+#-------------------------------------------------------------------------
+
+subdir = src/backend/port
+top_builddir = ../../..
+include $(top_builddir)/src/Makefile.global
+
+OBJS = \
+	$(TAS) \
+	atomics.o \
+	pg_sema.o \
+	pg_shmem.o
+
+ifeq ($(PORTNAME), win32)
+SUBDIRS += win32
+endif
+
+include $(top_srcdir)/src/backend/common.mk
+
+tas.o: tas.s
+ifeq ($(SUN_STUDIO_CC), yes)
+# preprocess assembler file with cpp
+	$(CC) $(CFLAGS) -c -P $<
+	mv $*.i $*_cpp.s
+	$(CC) $(CFLAGS) -c $*_cpp.s -o $@
+else
+	$(CC) $(CFLAGS) -c $<
+endif
+
+distclean clean:
+	rm -f tas_cpp.s
+	$(MAKE) -C win32 clean
diff --git a/src/backend/port/aix/mkldexport.sh b/src/backend/port/aix/mkldexport.sh
new file mode 100755
index 0000000..adf3793
--- /dev/null
+++ b/src/backend/port/aix/mkldexport.sh
@@ -0,0 +1,61 @@
+#!/bin/sh
+#
+# mkldexport
+#	create an AIX exports file from an object file
+#
+# src/backend/port/aix/mkldexport.sh
+#
+# Usage:
+#	mkldexport objectfile [location]
+# where
+#	objectfile is the current location of the object file.
+#	location is the eventual (installed) location of the
+#		object file (if different from the current
+#		working directory).
+#
+# [This file comes from the Postgres 4.2 distribution. - ay 7/95]
+#
+# Header: /usr/local/devel/postgres/src/tools/mkldexport/RCS/mkldexport.sh,v 1.2 1994/03/13 04:59:12 aoki Exp
+#
+
+# setting this to nm -B might be better
+# ... due to changes in AIX 4.x ...
+# ... let us search in different directories - Gerhard Reithofer
+if [ -x /usr/ucb/nm ]
+then NM=/usr/ucb/nm
+elif [ -x /usr/bin/nm ]
+then NM=/usr/bin/nm
+elif [ -x /usr/ccs/bin/nm ]
+then NM=/usr/ccs/bin/nm
+elif [ -x /usr/usg/bin/nm ]
+then NM=/usr/usg/bin/nm
+else echo "Fatal error: cannot find `nm' ... please check your installation."
+     exit 1
+fi
+
+CMDNAME=`basename $0`
+if [ -z "$1" ]; then
+	echo "Usage: $CMDNAME object [location]"
+	exit 1
+fi
+OBJNAME=`basename $1`
+if [ "`basename $OBJNAME`" != "`basename $OBJNAME .o`" ]; then
+	OBJNAME=`basename $OBJNAME .o`.so
+fi
+if [ -z "$2" ]; then
+	echo '#!'
+else
+	if [ "$2" = "." ]; then
+		# for the base executable (AIX 4.2 and up)
+		echo '#! .'
+	else
+		echo '#!' $2
+	fi
+fi
+$NM -BCg $1 | \
+	egrep ' [TDB] ' | \
+	sed -e 's/.* //' | \
+	egrep -v '\$' | \
+	sed -e 's/^[.]//' | \
+	sort | \
+	uniq
diff --git a/src/backend/port/atomics.c b/src/backend/port/atomics.c
new file mode 100644
index 0000000..c4f8370
--- /dev/null
+++ b/src/backend/port/atomics.c
@@ -0,0 +1,239 @@
+/*-------------------------------------------------------------------------
+ *
+ * atomics.c
+ *	   Non-Inline parts of the atomics implementation
+ *
+ * Portions Copyright (c) 2013-2020, PostgreSQL Global Development Group
+ *
+ *
+ * IDENTIFICATION
+ *	  src/backend/port/atomics.c
+ *
+ *-------------------------------------------------------------------------
+ */
+#include "postgres.h"
+
+#include "miscadmin.h"
+#include "port/atomics.h"
+#include "storage/spin.h"
+
+#ifdef PG_HAVE_MEMORY_BARRIER_EMULATION
+#ifdef WIN32
+#error "barriers are required (and provided) on WIN32 platforms"
+#endif
+#include <signal.h>
+#endif
+
+#ifdef PG_HAVE_MEMORY_BARRIER_EMULATION
+void
+pg_spinlock_barrier(void)
+{
+	/*
+	 * NB: we have to be reentrant here, some barriers are placed in signal
+	 * handlers.
+	 *
+	 * We use kill(0) for the fallback barrier as we assume that kernels on
+	 * systems old enough to require fallback barrier support will include an
+	 * appropriate barrier while checking the existence of the postmaster pid.
+	 */
+	(void) kill(PostmasterPid, 0);
+}
+#endif
+
+#ifdef PG_HAVE_COMPILER_BARRIER_EMULATION
+void
+pg_extern_compiler_barrier(void)
+{
+	/* do nothing */
+}
+#endif
+
+
+#ifdef PG_HAVE_ATOMIC_FLAG_SIMULATION
+
+void
+pg_atomic_init_flag_impl(volatile pg_atomic_flag *ptr)
+{
+	StaticAssertStmt(sizeof(ptr->sema) >= sizeof(slock_t),
+					 "size mismatch of atomic_flag vs slock_t");
+
+#ifndef HAVE_SPINLOCKS
+
+	/*
+	 * NB: If we're using semaphore based TAS emulation, be careful to use a
+	 * separate set of semaphores. Otherwise we'd get in trouble if an atomic
+	 * var would be manipulated while spinlock is held.
+	 */
+	s_init_lock_sema((slock_t *) &ptr->sema, true);
+#else
+	SpinLockInit((slock_t *) &ptr->sema);
+#endif
+
+	ptr->value = false;
+}
+
+bool
+pg_atomic_test_set_flag_impl(volatile pg_atomic_flag *ptr)
+{
+	uint32		oldval;
+
+	SpinLockAcquire((slock_t *) &ptr->sema);
+	oldval = ptr->value;
+	ptr->value = true;
+	SpinLockRelease((slock_t *) &ptr->sema);
+
+	return oldval == 0;
+}
+
+void
+pg_atomic_clear_flag_impl(volatile pg_atomic_flag *ptr)
+{
+	SpinLockAcquire((slock_t *) &ptr->sema);
+	ptr->value = false;
+	SpinLockRelease((slock_t *) &ptr->sema);
+}
+
+bool
+pg_atomic_unlocked_test_flag_impl(volatile pg_atomic_flag *ptr)
+{
+	return ptr->value == 0;
+}
+
+#endif							/* PG_HAVE_ATOMIC_FLAG_SIMULATION */
+
+#ifdef PG_HAVE_ATOMIC_U32_SIMULATION
+void
+pg_atomic_init_u32_impl(volatile pg_atomic_uint32 *ptr, uint32 val_)
+{
+	StaticAssertStmt(sizeof(ptr->sema) >= sizeof(slock_t),
+					 "size mismatch of atomic_uint32 vs slock_t");
+
+	/*
+	 * If we're using semaphore based atomic flags, be careful about nested
+	 * usage of atomics while a spinlock is held.
+	 */
+#ifndef HAVE_SPINLOCKS
+	s_init_lock_sema((slock_t *) &ptr->sema, true);
+#else
+	SpinLockInit((slock_t *) &ptr->sema);
+#endif
+	ptr->value = val_;
+}
+
+void
+pg_atomic_write_u32_impl(volatile pg_atomic_uint32 *ptr, uint32 val)
+{
+	/*
+	 * One might think that an unlocked write doesn't need to acquire the
+	 * spinlock, but one would be wrong. Even an unlocked write has to cause a
+	 * concurrent pg_atomic_compare_exchange_u32() (et al) to fail.
+	 */
+	SpinLockAcquire((slock_t *) &ptr->sema);
+	ptr->value = val;
+	SpinLockRelease((slock_t *) &ptr->sema);
+}
+
+bool
+pg_atomic_compare_exchange_u32_impl(volatile pg_atomic_uint32 *ptr,
+									uint32 *expected, uint32 newval)
+{
+	bool		ret;
+
+	/*
+	 * Do atomic op under a spinlock. It might look like we could just skip
+	 * the cmpxchg if the lock isn't available, but that'd just emulate a
+	 * 'weak' compare and swap. I.e. one that allows spurious failures. Since
+	 * several algorithms rely on a strong variant and that is efficiently
+	 * implementable on most major architectures let's emulate it here as
+	 * well.
+	 */
+	SpinLockAcquire((slock_t *) &ptr->sema);
+
+	/* perform compare/exchange logic */
+	ret = ptr->value == *expected;
+	*expected = ptr->value;
+	if (ret)
+		ptr->value = newval;
+
+	/* and release lock */
+	SpinLockRelease((slock_t *) &ptr->sema);
+
+	return ret;
+}
+
+uint32
+pg_atomic_fetch_add_u32_impl(volatile pg_atomic_uint32 *ptr, int32 add_)
+{
+	uint32		oldval;
+
+	SpinLockAcquire((slock_t *) &ptr->sema);
+	oldval = ptr->value;
+	ptr->value += add_;
+	SpinLockRelease((slock_t *) &ptr->sema);
+	return oldval;
+}
+
+#endif							/* PG_HAVE_ATOMIC_U32_SIMULATION */
+
+
+#ifdef PG_HAVE_ATOMIC_U64_SIMULATION
+
+void
+pg_atomic_init_u64_impl(volatile pg_atomic_uint64 *ptr, uint64 val_)
+{
+	StaticAssertStmt(sizeof(ptr->sema) >= sizeof(slock_t),
+					 "size mismatch of atomic_uint64 vs slock_t");
+
+	/*
+	 * If we're using semaphore based atomic flags, be careful about nested
+	 * usage of atomics while a spinlock is held.
+	 */
+#ifndef HAVE_SPINLOCKS
+	s_init_lock_sema((slock_t *) &ptr->sema, true);
+#else
+	SpinLockInit((slock_t *) &ptr->sema);
+#endif
+	ptr->value = val_;
+}
+
+bool
+pg_atomic_compare_exchange_u64_impl(volatile pg_atomic_uint64 *ptr,
+									uint64 *expected, uint64 newval)
+{
+	bool		ret;
+
+	/*
+	 * Do atomic op under a spinlock. It might look like we could just skip
+	 * the cmpxchg if the lock isn't available, but that'd just emulate a
+	 * 'weak' compare and swap. I.e. one that allows spurious failures. Since
+	 * several algorithms rely on a strong variant and that is efficiently
+	 * implementable on most major architectures let's emulate it here as
+	 * well.
+	 */
+	SpinLockAcquire((slock_t *) &ptr->sema);
+
+	/* perform compare/exchange logic */
+	ret = ptr->value == *expected;
+	*expected = ptr->value;
+	if (ret)
+		ptr->value = newval;
+
+	/* and release lock */
+	SpinLockRelease((slock_t *) &ptr->sema);
+
+	return ret;
+}
+
+uint64
+pg_atomic_fetch_add_u64_impl(volatile pg_atomic_uint64 *ptr, int64 add_)
+{
+	uint64		oldval;
+
+	SpinLockAcquire((slock_t *) &ptr->sema);
+	oldval = ptr->value;
+	ptr->value += add_;
+	SpinLockRelease((slock_t *) &ptr->sema);
+	return oldval;
+}
+
+#endif							/* PG_HAVE_ATOMIC_U64_SIMULATION */
diff --git a/src/backend/port/hpux/tas.c.template b/src/backend/port/hpux/tas.c.template
new file mode 100644
index 0000000..5ccbbcd
--- /dev/null
+++ b/src/backend/port/hpux/tas.c.template
@@ -0,0 +1,40 @@
+/*
+ * tas() for HPPA.
+ *
+ * To generate tas.s using this template:
+ *	1. cc +O2 -S -c tas.c
+ *	2. edit tas.s:
+ *		- replace the LDW with LDCWX
+ *	3. install as src/backend/port/tas/hpux_hppa.s.
+ *
+ * For details about the LDCWX instruction, see the "Precision
+ * Architecture and Instruction Reference Manual" (09740-90014 of June
+ * 1987), p. 5-38.
+ */
+
+int
+tas(lock)
+    int *lock;	/* LDCWX is a word instruction */
+{
+    /*
+     * LDCWX requires that we align the "semaphore" to a 16-byte
+     * boundary.  The actual datum is a single word (4 bytes).
+     */
+    lock = ((uintptr_t) lock + 15) & ~15;
+
+    /*
+     * The LDCWX instruction atomically clears the target word and
+     * returns the previous value.  Hence, if the instruction returns
+     * 0, someone else has already acquired the lock before we tested
+     * it (i.e., we have failed).
+     *
+     * Notice that this means that we actually clear the word to set
+     * the lock and set the word to clear the lock.  This is the
+     * opposite behavior from the SPARC LDSTUB instruction.  For some
+     * reason everything that H-P does is rather baroque...
+     */
+    if (*lock) {	/* this generates the LDW */
+	return(0);	/* success */
+    }
+    return(1);    	/* failure */
+}
diff --git a/src/backend/port/posix_sema.c b/src/backend/port/posix_sema.c
new file mode 100644
index 0000000..277b82c
--- /dev/null
+++ b/src/backend/port/posix_sema.c
@@ -0,0 +1,388 @@
+/*-------------------------------------------------------------------------
+ *
+ * posix_sema.c
+ *	  Implement PGSemaphores using POSIX semaphore facilities
+ *
+ * We prefer the unnamed style of POSIX semaphore (the kind made with
+ * sem_init).  We can cope with the kind made with sem_open, however.
+ *
+ * In either implementation, typedef PGSemaphore is equivalent to "sem_t *".
+ * With unnamed semaphores, the sem_t structs live in an array in shared
+ * memory.  With named semaphores, that's not true because we cannot persuade
+ * sem_open to do its allocation there.  Therefore, the named-semaphore code
+ * *does not cope with EXEC_BACKEND*.  The sem_t structs will just be in the
+ * postmaster's private memory, where they are successfully inherited by
+ * forked backends, but they could not be accessed by exec'd backends.
+ *
+ *
+ * Portions Copyright (c) 1996-2020, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ * IDENTIFICATION
+ *	  src/backend/port/posix_sema.c
+ *
+ *-------------------------------------------------------------------------
+ */
+#include "postgres.h"
+
+#include <fcntl.h>
+#include <semaphore.h>
+#include <signal.h>
+#include <unistd.h>
+#include <sys/stat.h>
+
+#include "miscadmin.h"
+#include "storage/ipc.h"
+#include "storage/pg_sema.h"
+#include "storage/shmem.h"
+
+
+/* see file header comment */
+#if defined(USE_NAMED_POSIX_SEMAPHORES) && defined(EXEC_BACKEND)
+#error cannot use named POSIX semaphores with EXEC_BACKEND
+#endif
+
+typedef union SemTPadded
+{
+	sem_t		pgsem;
+	char		pad[PG_CACHE_LINE_SIZE];
+} SemTPadded;
+
+/* typedef PGSemaphore is equivalent to pointer to sem_t */
+typedef struct PGSemaphoreData
+{
+	SemTPadded	sem_padded;
+} PGSemaphoreData;
+
+#define PG_SEM_REF(x)	(&(x)->sem_padded.pgsem)
+
+#define IPCProtection	(0600)	/* access/modify by user only */
+
+#ifdef USE_NAMED_POSIX_SEMAPHORES
+static sem_t **mySemPointers;	/* keep track of created semaphores */
+#else
+static PGSemaphore sharedSemas; /* array of PGSemaphoreData in shared memory */
+#endif
+static int	numSems;			/* number of semas acquired so far */
+static int	maxSems;			/* allocated size of above arrays */
+static int	nextSemKey;			/* next name to try */
+
+
+static void ReleaseSemaphores(int status, Datum arg);
+
+
+#ifdef USE_NAMED_POSIX_SEMAPHORES
+
+/*
+ * PosixSemaphoreCreate
+ *
+ * Attempt to create a new named semaphore.
+ *
+ * If we fail with a failure code other than collision-with-existing-sema,
+ * print out an error and abort.  Other types of errors suggest nonrecoverable
+ * problems.
+ */
+static sem_t *
+PosixSemaphoreCreate(void)
+{
+	int			semKey;
+	char		semname[64];
+	sem_t	   *mySem;
+
+	for (;;)
+	{
+		semKey = nextSemKey++;
+
+		snprintf(semname, sizeof(semname), "/pgsql-%d", semKey);
+
+		mySem = sem_open(semname, O_CREAT | O_EXCL,
+						 (mode_t) IPCProtection, (unsigned) 1);
+
+#ifdef SEM_FAILED
+		if (mySem != (sem_t *) SEM_FAILED)
+			break;
+#else
+		if (mySem != (sem_t *) (-1))
+			break;
+#endif
+
+		/* Loop if error indicates a collision */
+		if (errno == EEXIST || errno == EACCES || errno == EINTR)
+			continue;
+
+		/*
+		 * Else complain and abort
+		 */
+		elog(FATAL, "sem_open(\"%s\") failed: %m", semname);
+	}
+
+	/*
+	 * Unlink the semaphore immediately, so it can't be accessed externally.
+	 * This also ensures that it will go away if we crash.
+	 */
+	sem_unlink(semname);
+
+	return mySem;
+}
+#else							/* !USE_NAMED_POSIX_SEMAPHORES */
+
+/*
+ * PosixSemaphoreCreate
+ *
+ * Attempt to create a new unnamed semaphore.
+ */
+static void
+PosixSemaphoreCreate(sem_t *sem)
+{
+	if (sem_init(sem, 1, 1) < 0)
+		elog(FATAL, "sem_init failed: %m");
+}
+#endif							/* USE_NAMED_POSIX_SEMAPHORES */
+
+
+/*
+ * PosixSemaphoreKill	- removes a semaphore
+ */
+static void
+PosixSemaphoreKill(sem_t *sem)
+{
+#ifdef USE_NAMED_POSIX_SEMAPHORES
+	/* Got to use sem_close for named semaphores */
+	if (sem_close(sem) < 0)
+		elog(LOG, "sem_close failed: %m");
+#else
+	/* Got to use sem_destroy for unnamed semaphores */
+	if (sem_destroy(sem) < 0)
+		elog(LOG, "sem_destroy failed: %m");
+#endif
+}
+
+
+/*
+ * Report amount of shared memory needed for semaphores
+ */
+Size
+PGSemaphoreShmemSize(int maxSemas)
+{
+#ifdef USE_NAMED_POSIX_SEMAPHORES
+	/* No shared memory needed in this case */
+	return 0;
+#else
+	/* Need a PGSemaphoreData per semaphore */
+	return mul_size(maxSemas, sizeof(PGSemaphoreData));
+#endif
+}
+
+/*
+ * PGReserveSemaphores --- initialize semaphore support
+ *
+ * This is called during postmaster start or shared memory reinitialization.
+ * It should do whatever is needed to be able to support up to maxSemas
+ * subsequent PGSemaphoreCreate calls.  Also, if any system resources
+ * are acquired here or in PGSemaphoreCreate, register an on_shmem_exit
+ * callback to release them.
+ *
+ * In the Posix implementation, we acquire semaphores on-demand; the
+ * maxSemas parameter is just used to size the arrays.  For unnamed
+ * semaphores, there is an array of PGSemaphoreData structs in shared memory.
+ * For named semaphores, we keep a postmaster-local array of sem_t pointers,
+ * which we use for releasing the semaphores when done.
+ * (This design minimizes the dependency of postmaster shutdown on the
+ * contents of shared memory, which a failed backend might have clobbered.
+ * We can't do much about the possibility of sem_destroy() crashing, but
+ * we don't have to expose the counters to other processes.)
+ */
+void
+PGReserveSemaphores(int maxSemas)
+{
+	struct stat statbuf;
+
+	/*
+	 * We use the data directory's inode number to seed the search for free
+	 * semaphore keys.  This minimizes the odds of collision with other
+	 * postmasters, while maximizing the odds that we will detect and clean up
+	 * semaphores left over from a crashed postmaster in our own directory.
+	 */
+	if (stat(DataDir, &statbuf) < 0)
+		ereport(FATAL,
+				(errcode_for_file_access(),
+				 errmsg("could not stat data directory \"%s\": %m",
+						DataDir)));
+
+#ifdef USE_NAMED_POSIX_SEMAPHORES
+	mySemPointers = (sem_t **) malloc(maxSemas * sizeof(sem_t *));
+	if (mySemPointers == NULL)
+		elog(PANIC, "out of memory");
+#else
+
+	/*
+	 * We must use ShmemAllocUnlocked(), since the spinlock protecting
+	 * ShmemAlloc() won't be ready yet.  (This ordering is necessary when we
+	 * are emulating spinlocks with semaphores.)
+	 */
+	sharedSemas = (PGSemaphore)
+		ShmemAllocUnlocked(PGSemaphoreShmemSize(maxSemas));
+#endif
+
+	numSems = 0;
+	maxSems = maxSemas;
+	nextSemKey = statbuf.st_ino;
+
+	on_shmem_exit(ReleaseSemaphores, 0);
+}
+
+/*
+ * Release semaphores at shutdown or shmem reinitialization
+ *
+ * (called as an on_shmem_exit callback, hence funny argument list)
+ */
+static void
+ReleaseSemaphores(int status, Datum arg)
+{
+	int			i;
+
+#ifdef USE_NAMED_POSIX_SEMAPHORES
+	for (i = 0; i < numSems; i++)
+		PosixSemaphoreKill(mySemPointers[i]);
+	free(mySemPointers);
+#endif
+
+#ifdef USE_UNNAMED_POSIX_SEMAPHORES
+	for (i = 0; i < numSems; i++)
+		PosixSemaphoreKill(PG_SEM_REF(sharedSemas + i));
+#endif
+}
+
+/*
+ * PGSemaphoreCreate
+ *
+ * Allocate a PGSemaphore structure with initial count 1
+ */
+PGSemaphore
+PGSemaphoreCreate(void)
+{
+	PGSemaphore sema;
+	sem_t	   *newsem;
+
+	/* Can't do this in a backend, because static state is postmaster's */
+	Assert(!IsUnderPostmaster);
+
+	if (numSems >= maxSems)
+		elog(PANIC, "too many semaphores created");
+
+#ifdef USE_NAMED_POSIX_SEMAPHORES
+	newsem = PosixSemaphoreCreate();
+	/* Remember new sema for ReleaseSemaphores */
+	mySemPointers[numSems] = newsem;
+	sema = (PGSemaphore) newsem;
+#else
+	sema = &sharedSemas[numSems];
+	newsem = PG_SEM_REF(sema);
+	PosixSemaphoreCreate(newsem);
+#endif
+
+	numSems++;
+
+	return sema;
+}
+
+/*
+ * PGSemaphoreReset
+ *
+ * Reset a previously-initialized PGSemaphore to have count 0
+ */
+void
+PGSemaphoreReset(PGSemaphore sema)
+{
+	/*
+	 * There's no direct API for this in POSIX, so we have to ratchet the
+	 * semaphore down to 0 with repeated trywait's.
+	 */
+	for (;;)
+	{
+		if (sem_trywait(PG_SEM_REF(sema)) < 0)
+		{
+			if (errno == EAGAIN || errno == EDEADLK)
+				break;			/* got it down to 0 */
+			if (errno == EINTR)
+				continue;		/* can this happen? */
+			elog(FATAL, "sem_trywait failed: %m");
+		}
+	}
+}
+
+/*
+ * PGSemaphoreLock
+ *
+ * Lock a semaphore (decrement count), blocking if count would be < 0
+ */
+void
+PGSemaphoreLock(PGSemaphore sema)
+{
+	int			errStatus;
+
+	/* See notes in sysv_sema.c's implementation of PGSemaphoreLock. */
+	do
+	{
+		errStatus = sem_wait(PG_SEM_REF(sema));
+	} while (errStatus < 0 && errno == EINTR);
+
+	if (errStatus < 0)
+		elog(FATAL, "sem_wait failed: %m");
+}
+
+/*
+ * PGSemaphoreUnlock
+ *
+ * Unlock a semaphore (increment count)
+ */
+void
+PGSemaphoreUnlock(PGSemaphore sema)
+{
+	int			errStatus;
+
+	/*
+	 * Note: if errStatus is -1 and errno == EINTR then it means we returned
+	 * from the operation prematurely because we were sent a signal.  So we
+	 * try and unlock the semaphore again. Not clear this can really happen,
+	 * but might as well cope.
+	 */
+	do
+	{
+		errStatus = sem_post(PG_SEM_REF(sema));
+	} while (errStatus < 0 && errno == EINTR);
+
+	if (errStatus < 0)
+		elog(FATAL, "sem_post failed: %m");
+}
+
+/*
+ * PGSemaphoreTryLock
+ *
+ * Lock a semaphore only if able to do so without blocking
+ */
+bool
+PGSemaphoreTryLock(PGSemaphore sema)
+{
+	int			errStatus;
+
+	/*
+	 * Note: if errStatus is -1 and errno == EINTR then it means we returned
+	 * from the operation prematurely because we were sent a signal.  So we
+	 * try and lock the semaphore again.
+	 */
+	do
+	{
+		errStatus = sem_trywait(PG_SEM_REF(sema));
+	} while (errStatus < 0 && errno == EINTR);
+
+	if (errStatus < 0)
+	{
+		if (errno == EAGAIN || errno == EDEADLK)
+			return false;		/* failed to lock it */
+		/* Otherwise we got trouble */
+		elog(FATAL, "sem_trywait failed: %m");
+	}
+
+	return true;
+}
diff --git a/src/backend/port/sysv_sema.c b/src/backend/port/sysv_sema.c
new file mode 100644
index 0000000..88c2862
--- /dev/null
+++ b/src/backend/port/sysv_sema.c
@@ -0,0 +1,517 @@
+/*-------------------------------------------------------------------------
+ *
+ * sysv_sema.c
+ *	  Implement PGSemaphores using SysV semaphore facilities
+ *
+ *
+ * Portions Copyright (c) 1996-2020, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ * IDENTIFICATION
+ *	  src/backend/port/sysv_sema.c
+ *
+ *-------------------------------------------------------------------------
+ */
+#include "postgres.h"
+
+#include <signal.h>
+#include <unistd.h>
+#include <sys/file.h>
+#include <sys/stat.h>
+#ifdef HAVE_SYS_IPC_H
+#include <sys/ipc.h>
+#endif
+#ifdef HAVE_SYS_SEM_H
+#include <sys/sem.h>
+#endif
+
+#include "miscadmin.h"
+#include "storage/ipc.h"
+#include "storage/pg_sema.h"
+#include "storage/shmem.h"
+
+
+typedef struct PGSemaphoreData
+{
+	int			semId;			/* semaphore set identifier */
+	int			semNum;			/* semaphore number within set */
+} PGSemaphoreData;
+
+#ifndef HAVE_UNION_SEMUN
+union semun
+{
+	int			val;
+	struct semid_ds *buf;
+	unsigned short *array;
+};
+#endif
+
+typedef key_t IpcSemaphoreKey;	/* semaphore key passed to semget(2) */
+typedef int IpcSemaphoreId;		/* semaphore ID returned by semget(2) */
+
+/*
+ * SEMAS_PER_SET is the number of useful semaphores in each semaphore set
+ * we allocate.  It must be *less than* your kernel's SEMMSL (max semaphores
+ * per set) parameter, which is often around 25.  (Less than, because we
+ * allocate one extra sema in each set for identification purposes.)
+ */
+#define SEMAS_PER_SET	16
+
+#define IPCProtection	(0600)	/* access/modify by user only */
+
+#define PGSemaMagic		537		/* must be less than SEMVMX */
+
+
+static PGSemaphore sharedSemas; /* array of PGSemaphoreData in shared memory */
+static int	numSharedSemas;		/* number of PGSemaphoreDatas used so far */
+static int	maxSharedSemas;		/* allocated size of PGSemaphoreData array */
+static IpcSemaphoreId *mySemaSets;	/* IDs of sema sets acquired so far */
+static int	numSemaSets;		/* number of sema sets acquired so far */
+static int	maxSemaSets;		/* allocated size of mySemaSets array */
+static IpcSemaphoreKey nextSemaKey; /* next key to try using */
+static int	nextSemaNumber;		/* next free sem num in last sema set */
+
+
+static IpcSemaphoreId InternalIpcSemaphoreCreate(IpcSemaphoreKey semKey,
+												 int numSems);
+static void IpcSemaphoreInitialize(IpcSemaphoreId semId, int semNum,
+								   int value);
+static void IpcSemaphoreKill(IpcSemaphoreId semId);
+static int	IpcSemaphoreGetValue(IpcSemaphoreId semId, int semNum);
+static pid_t IpcSemaphoreGetLastPID(IpcSemaphoreId semId, int semNum);
+static IpcSemaphoreId IpcSemaphoreCreate(int numSems);
+static void ReleaseSemaphores(int status, Datum arg);
+
+
+/*
+ * InternalIpcSemaphoreCreate
+ *
+ * Attempt to create a new semaphore set with the specified key.
+ * Will fail (return -1) if such a set already exists.
+ *
+ * If we fail with a failure code other than collision-with-existing-set,
+ * print out an error and abort.  Other types of errors suggest nonrecoverable
+ * problems.
+ */
+static IpcSemaphoreId
+InternalIpcSemaphoreCreate(IpcSemaphoreKey semKey, int numSems)
+{
+	int			semId;
+
+	semId = semget(semKey, numSems, IPC_CREAT | IPC_EXCL | IPCProtection);
+
+	if (semId < 0)
+	{
+		int			saved_errno = errno;
+
+		/*
+		 * Fail quietly if error indicates a collision with existing set. One
+		 * would expect EEXIST, given that we said IPC_EXCL, but perhaps we
+		 * could get a permission violation instead?  Also, EIDRM might occur
+		 * if an old set is slated for destruction but not gone yet.
+		 */
+		if (saved_errno == EEXIST || saved_errno == EACCES
+#ifdef EIDRM
+			|| saved_errno == EIDRM
+#endif
+			)
+			return -1;
+
+		/*
+		 * Else complain and abort
+		 */
+		ereport(FATAL,
+				(errmsg("could not create semaphores: %m"),
+				 errdetail("Failed system call was semget(%lu, %d, 0%o).",
+						   (unsigned long) semKey, numSems,
+						   IPC_CREAT | IPC_EXCL | IPCProtection),
+				 (saved_errno == ENOSPC) ?
+				 errhint("This error does *not* mean that you have run out of disk space.  "
+						 "It occurs when either the system limit for the maximum number of "
+						 "semaphore sets (SEMMNI), or the system wide maximum number of "
+						 "semaphores (SEMMNS), would be exceeded.  You need to raise the "
+						 "respective kernel parameter.  Alternatively, reduce PostgreSQL's "
+						 "consumption of semaphores by reducing its max_connections parameter.\n"
+						 "The PostgreSQL documentation contains more information about "
+						 "configuring your system for PostgreSQL.") : 0));
+	}
+
+	return semId;
+}
+
+/*
+ * Initialize a semaphore to the specified value.
+ */
+static void
+IpcSemaphoreInitialize(IpcSemaphoreId semId, int semNum, int value)
+{
+	union semun semun;
+
+	semun.val = value;
+	if (semctl(semId, semNum, SETVAL, semun) < 0)
+	{
+		int			saved_errno = errno;
+
+		ereport(FATAL,
+				(errmsg_internal("semctl(%d, %d, SETVAL, %d) failed: %m",
+								 semId, semNum, value),
+				 (saved_errno == ERANGE) ?
+				 errhint("You possibly need to raise your kernel's SEMVMX value to be at least "
+						 "%d.  Look into the PostgreSQL documentation for details.",
+						 value) : 0));
+	}
+}
+
+/*
+ * IpcSemaphoreKill(semId)	- removes a semaphore set
+ */
+static void
+IpcSemaphoreKill(IpcSemaphoreId semId)
+{
+	union semun semun;
+
+	semun.val = 0;				/* unused, but keep compiler quiet */
+
+	if (semctl(semId, 0, IPC_RMID, semun) < 0)
+		elog(LOG, "semctl(%d, 0, IPC_RMID, ...) failed: %m", semId);
+}
+
+/* Get the current value (semval) of the semaphore */
+static int
+IpcSemaphoreGetValue(IpcSemaphoreId semId, int semNum)
+{
+	union semun dummy;			/* for Solaris */
+
+	dummy.val = 0;				/* unused */
+
+	return semctl(semId, semNum, GETVAL, dummy);
+}
+
+/* Get the PID of the last process to do semop() on the semaphore */
+static pid_t
+IpcSemaphoreGetLastPID(IpcSemaphoreId semId, int semNum)
+{
+	union semun dummy;			/* for Solaris */
+
+	dummy.val = 0;				/* unused */
+
+	return semctl(semId, semNum, GETPID, dummy);
+}
+
+
+/*
+ * Create a semaphore set with the given number of useful semaphores
+ * (an additional sema is actually allocated to serve as identifier).
+ * Dead Postgres sema sets are recycled if found, but we do not fail
+ * upon collision with non-Postgres sema sets.
+ *
+ * The idea here is to detect and re-use keys that may have been assigned
+ * by a crashed postmaster or backend.
+ */
+static IpcSemaphoreId
+IpcSemaphoreCreate(int numSems)
+{
+	IpcSemaphoreId semId;
+	union semun semun;
+	PGSemaphoreData mysema;
+
+	/* Loop till we find a free IPC key */
+	for (nextSemaKey++;; nextSemaKey++)
+	{
+		pid_t		creatorPID;
+
+		/* Try to create new semaphore set */
+		semId = InternalIpcSemaphoreCreate(nextSemaKey, numSems + 1);
+		if (semId >= 0)
+			break;				/* successful create */
+
+		/* See if it looks to be leftover from a dead Postgres process */
+		semId = semget(nextSemaKey, numSems + 1, 0);
+		if (semId < 0)
+			continue;			/* failed: must be some other app's */
+		if (IpcSemaphoreGetValue(semId, numSems) != PGSemaMagic)
+			continue;			/* sema belongs to a non-Postgres app */
+
+		/*
+		 * If the creator PID is my own PID or does not belong to any extant
+		 * process, it's safe to zap it.
+		 */
+		creatorPID = IpcSemaphoreGetLastPID(semId, numSems);
+		if (creatorPID <= 0)
+			continue;			/* oops, GETPID failed */
+		if (creatorPID != getpid())
+		{
+			if (kill(creatorPID, 0) == 0 || errno != ESRCH)
+				continue;		/* sema belongs to a live process */
+		}
+
+		/*
+		 * The sema set appears to be from a dead Postgres process, or from a
+		 * previous cycle of life in this same process.  Zap it, if possible.
+		 * This probably shouldn't fail, but if it does, assume the sema set
+		 * belongs to someone else after all, and continue quietly.
+		 */
+		semun.val = 0;			/* unused, but keep compiler quiet */
+		if (semctl(semId, 0, IPC_RMID, semun) < 0)
+			continue;
+
+		/*
+		 * Now try again to create the sema set.
+		 */
+		semId = InternalIpcSemaphoreCreate(nextSemaKey, numSems + 1);
+		if (semId >= 0)
+			break;				/* successful create */
+
+		/*
+		 * Can only get here if some other process managed to create the same
+		 * sema key before we did.  Let him have that one, loop around to try
+		 * next key.
+		 */
+	}
+
+	/*
+	 * OK, we created a new sema set.  Mark it as created by this process. We
+	 * do this by setting the spare semaphore to PGSemaMagic-1 and then
+	 * incrementing it with semop().  That leaves it with value PGSemaMagic
+	 * and sempid referencing this process.
+	 */
+	IpcSemaphoreInitialize(semId, numSems, PGSemaMagic - 1);
+	mysema.semId = semId;
+	mysema.semNum = numSems;
+	PGSemaphoreUnlock(&mysema);
+
+	return semId;
+}
+
+
+/*
+ * Report amount of shared memory needed for semaphores
+ */
+Size
+PGSemaphoreShmemSize(int maxSemas)
+{
+	return mul_size(maxSemas, sizeof(PGSemaphoreData));
+}
+
+/*
+ * PGReserveSemaphores --- initialize semaphore support
+ *
+ * This is called during postmaster start or shared memory reinitialization.
+ * It should do whatever is needed to be able to support up to maxSemas
+ * subsequent PGSemaphoreCreate calls.  Also, if any system resources
+ * are acquired here or in PGSemaphoreCreate, register an on_shmem_exit
+ * callback to release them.
+ *
+ * In the SysV implementation, we acquire semaphore sets on-demand; the
+ * maxSemas parameter is just used to size the arrays.  There is an array
+ * of PGSemaphoreData structs in shared memory, and a postmaster-local array
+ * with one entry per SysV semaphore set, which we use for releasing the
+ * semaphore sets when done.  (This design ensures that postmaster shutdown
+ * doesn't rely on the contents of shared memory, which a failed backend might
+ * have clobbered.)
+ */
+void
+PGReserveSemaphores(int maxSemas)
+{
+	struct stat statbuf;
+
+	/*
+	 * We use the data directory's inode number to seed the search for free
+	 * semaphore keys.  This minimizes the odds of collision with other
+	 * postmasters, while maximizing the odds that we will detect and clean up
+	 * semaphores left over from a crashed postmaster in our own directory.
+	 */
+	if (stat(DataDir, &statbuf) < 0)
+		ereport(FATAL,
+				(errcode_for_file_access(),
+				 errmsg("could not stat data directory \"%s\": %m",
+						DataDir)));
+
+	/*
+	 * We must use ShmemAllocUnlocked(), since the spinlock protecting
+	 * ShmemAlloc() won't be ready yet.  (This ordering is necessary when we
+	 * are emulating spinlocks with semaphores.)
+	 */
+	sharedSemas = (PGSemaphore)
+		ShmemAllocUnlocked(PGSemaphoreShmemSize(maxSemas));
+	numSharedSemas = 0;
+	maxSharedSemas = maxSemas;
+
+	maxSemaSets = (maxSemas + SEMAS_PER_SET - 1) / SEMAS_PER_SET;
+	mySemaSets = (IpcSemaphoreId *)
+		malloc(maxSemaSets * sizeof(IpcSemaphoreId));
+	if (mySemaSets == NULL)
+		elog(PANIC, "out of memory");
+	numSemaSets = 0;
+	nextSemaKey = statbuf.st_ino;
+	nextSemaNumber = SEMAS_PER_SET; /* force sema set alloc on 1st call */
+
+	on_shmem_exit(ReleaseSemaphores, 0);
+}
+
+/*
+ * Release semaphores at shutdown or shmem reinitialization
+ *
+ * (called as an on_shmem_exit callback, hence funny argument list)
+ */
+static void
+ReleaseSemaphores(int status, Datum arg)
+{
+	int			i;
+
+	for (i = 0; i < numSemaSets; i++)
+		IpcSemaphoreKill(mySemaSets[i]);
+	free(mySemaSets);
+}
+
+/*
+ * PGSemaphoreCreate
+ *
+ * Allocate a PGSemaphore structure with initial count 1
+ */
+PGSemaphore
+PGSemaphoreCreate(void)
+{
+	PGSemaphore sema;
+
+	/* Can't do this in a backend, because static state is postmaster's */
+	Assert(!IsUnderPostmaster);
+
+	if (nextSemaNumber >= SEMAS_PER_SET)
+	{
+		/* Time to allocate another semaphore set */
+		if (numSemaSets >= maxSemaSets)
+			elog(PANIC, "too many semaphores created");
+		mySemaSets[numSemaSets] = IpcSemaphoreCreate(SEMAS_PER_SET);
+		numSemaSets++;
+		nextSemaNumber = 0;
+	}
+	/* Use the next shared PGSemaphoreData */
+	if (numSharedSemas >= maxSharedSemas)
+		elog(PANIC, "too many semaphores created");
+	sema = &sharedSemas[numSharedSemas++];
+	/* Assign the next free semaphore in the current set */
+	sema->semId = mySemaSets[numSemaSets - 1];
+	sema->semNum = nextSemaNumber++;
+	/* Initialize it to count 1 */
+	IpcSemaphoreInitialize(sema->semId, sema->semNum, 1);
+
+	return sema;
+}
+
+/*
+ * PGSemaphoreReset
+ *
+ * Reset a previously-initialized PGSemaphore to have count 0
+ */
+void
+PGSemaphoreReset(PGSemaphore sema)
+{
+	IpcSemaphoreInitialize(sema->semId, sema->semNum, 0);
+}
+
+/*
+ * PGSemaphoreLock
+ *
+ * Lock a semaphore (decrement count), blocking if count would be < 0
+ */
+void
+PGSemaphoreLock(PGSemaphore sema)
+{
+	int			errStatus;
+	struct sembuf sops;
+
+	sops.sem_op = -1;			/* decrement */
+	sops.sem_flg = 0;
+	sops.sem_num = sema->semNum;
+
+	/*
+	 * Note: if errStatus is -1 and errno == EINTR then it means we returned
+	 * from the operation prematurely because we were sent a signal.  So we
+	 * try and lock the semaphore again.
+	 *
+	 * We used to check interrupts here, but that required servicing
+	 * interrupts directly from signal handlers. Which is hard to do safely
+	 * and portably.
+	 */
+	do
+	{
+		errStatus = semop(sema->semId, &sops, 1);
+	} while (errStatus < 0 && errno == EINTR);
+
+	if (errStatus < 0)
+		elog(FATAL, "semop(id=%d) failed: %m", sema->semId);
+}
+
+/*
+ * PGSemaphoreUnlock
+ *
+ * Unlock a semaphore (increment count)
+ */
+void
+PGSemaphoreUnlock(PGSemaphore sema)
+{
+	int			errStatus;
+	struct sembuf sops;
+
+	sops.sem_op = 1;			/* increment */
+	sops.sem_flg = 0;
+	sops.sem_num = sema->semNum;
+
+	/*
+	 * Note: if errStatus is -1 and errno == EINTR then it means we returned
+	 * from the operation prematurely because we were sent a signal.  So we
+	 * try and unlock the semaphore again. Not clear this can really happen,
+	 * but might as well cope.
+	 */
+	do
+	{
+		errStatus = semop(sema->semId, &sops, 1);
+	} while (errStatus < 0 && errno == EINTR);
+
+	if (errStatus < 0)
+		elog(FATAL, "semop(id=%d) failed: %m", sema->semId);
+}
+
+/*
+ * PGSemaphoreTryLock
+ *
+ * Lock a semaphore only if able to do so without blocking
+ */
+bool
+PGSemaphoreTryLock(PGSemaphore sema)
+{
+	int			errStatus;
+	struct sembuf sops;
+
+	sops.sem_op = -1;			/* decrement */
+	sops.sem_flg = IPC_NOWAIT;	/* but don't block */
+	sops.sem_num = sema->semNum;
+
+	/*
+	 * Note: if errStatus is -1 and errno == EINTR then it means we returned
+	 * from the operation prematurely because we were sent a signal.  So we
+	 * try and lock the semaphore again.
+	 */
+	do
+	{
+		errStatus = semop(sema->semId, &sops, 1);
+	} while (errStatus < 0 && errno == EINTR);
+
+	if (errStatus < 0)
+	{
+		/* Expect EAGAIN or EWOULDBLOCK (platform-dependent) */
+#ifdef EAGAIN
+		if (errno == EAGAIN)
+			return false;		/* failed to lock it */
+#endif
+#if defined(EWOULDBLOCK) && (!defined(EAGAIN) || (EWOULDBLOCK != EAGAIN))
+		if (errno == EWOULDBLOCK)
+			return false;		/* failed to lock it */
+#endif
+		/* Otherwise we got trouble */
+		elog(FATAL, "semop(id=%d) failed: %m", sema->semId);
+	}
+
+	return true;
+}
diff --git a/src/backend/port/sysv_shmem.c b/src/backend/port/sysv_shmem.c
new file mode 100644
index 0000000..198a698
--- /dev/null
+++ b/src/backend/port/sysv_shmem.c
@@ -0,0 +1,902 @@
+/*-------------------------------------------------------------------------
+ *
+ * sysv_shmem.c
+ *	  Implement shared memory using SysV facilities
+ *
+ * These routines used to be a fairly thin layer on top of SysV shared
+ * memory functionality.  With the addition of anonymous-shmem logic,
+ * they're a bit fatter now.  We still require a SysV shmem block to
+ * exist, though, because mmap'd shmem provides no way to find out how
+ * many processes are attached, which we need for interlocking purposes.
+ *
+ * Portions Copyright (c) 1996-2020, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ * IDENTIFICATION
+ *	  src/backend/port/sysv_shmem.c
+ *
+ *-------------------------------------------------------------------------
+ */
+#include "postgres.h"
+
+#include <signal.h>
+#include <unistd.h>
+#include <sys/file.h>
+#include <sys/mman.h>
+#include <sys/stat.h>
+#ifdef HAVE_SYS_IPC_H
+#include <sys/ipc.h>
+#endif
+#ifdef HAVE_SYS_SHM_H
+#include <sys/shm.h>
+#endif
+
+#include "miscadmin.h"
+#include "portability/mem.h"
+#include "storage/dsm.h"
+#include "storage/fd.h"
+#include "storage/ipc.h"
+#include "storage/pg_shmem.h"
+#include "utils/guc.h"
+#include "utils/pidfile.h"
+
+
+/*
+ * As of PostgreSQL 9.3, we normally allocate only a very small amount of
+ * System V shared memory, and only for the purposes of providing an
+ * interlock to protect the data directory.  The real shared memory block
+ * is allocated using mmap().  This works around the problem that many
+ * systems have very low limits on the amount of System V shared memory
+ * that can be allocated.  Even a limit of a few megabytes will be enough
+ * to run many copies of PostgreSQL without needing to adjust system settings.
+ *
+ * We assume that no one will attempt to run PostgreSQL 9.3 or later on
+ * systems that are ancient enough that anonymous shared memory is not
+ * supported, such as pre-2.4 versions of Linux.  If that turns out to be
+ * false, we might need to add compile and/or run-time tests here and do this
+ * only if the running kernel supports it.
+ *
+ * However, we must always disable this logic in the EXEC_BACKEND case, and
+ * fall back to the old method of allocating the entire segment using System V
+ * shared memory, because there's no way to attach an anonymous mmap'd segment
+ * to a process after exec().  Since EXEC_BACKEND is intended only for
+ * developer use, this shouldn't be a big problem.  Because of this, we do
+ * not worry about supporting anonymous shmem in the EXEC_BACKEND cases below.
+ *
+ * As of PostgreSQL 12, we regained the ability to use a large System V shared
+ * memory region even in non-EXEC_BACKEND builds, if shared_memory_type is set
+ * to sysv (though this is not the default).
+ */
+
+
+typedef key_t IpcMemoryKey;		/* shared memory key passed to shmget(2) */
+typedef int IpcMemoryId;		/* shared memory ID returned by shmget(2) */
+
+/*
+ * How does a given IpcMemoryId relate to this PostgreSQL process?
+ *
+ * One could recycle unattached segments of different data directories if we
+ * distinguished that case from other SHMSTATE_FOREIGN cases.  Doing so would
+ * cause us to visit less of the key space, making us less likely to detect a
+ * SHMSTATE_ATTACHED key.  It would also complicate the concurrency analysis,
+ * in that postmasters of different data directories could simultaneously
+ * attempt to recycle a given key.  We'll waste keys longer in some cases, but
+ * avoiding the problems of the alternative justifies that loss.
+ */
+typedef enum
+{
+	SHMSTATE_ANALYSIS_FAILURE,	/* unexpected failure to analyze the ID */
+	SHMSTATE_ATTACHED,			/* pertinent to DataDir, has attached PIDs */
+	SHMSTATE_ENOENT,			/* no segment of that ID */
+	SHMSTATE_FOREIGN,			/* exists, but not pertinent to DataDir */
+	SHMSTATE_UNATTACHED			/* pertinent to DataDir, no attached PIDs */
+} IpcMemoryState;
+
+
+unsigned long UsedShmemSegID = 0;
+void	   *UsedShmemSegAddr = NULL;
+
+static Size AnonymousShmemSize;
+static void *AnonymousShmem = NULL;
+
+static void *InternalIpcMemoryCreate(IpcMemoryKey memKey, Size size);
+static void IpcMemoryDetach(int status, Datum shmaddr);
+static void IpcMemoryDelete(int status, Datum shmId);
+static IpcMemoryState PGSharedMemoryAttach(IpcMemoryId shmId,
+										   void *attachAt,
+										   PGShmemHeader **addr);
+
+
+/*
+ *	InternalIpcMemoryCreate(memKey, size)
+ *
+ * Attempt to create a new shared memory segment with the specified key.
+ * Will fail (return NULL) if such a segment already exists.  If successful,
+ * attach the segment to the current process and return its attached address.
+ * On success, callbacks are registered with on_shmem_exit to detach and
+ * delete the segment when on_shmem_exit is called.
+ *
+ * If we fail with a failure code other than collision-with-existing-segment,
+ * print out an error and abort.  Other types of errors are not recoverable.
+ */
+static void *
+InternalIpcMemoryCreate(IpcMemoryKey memKey, Size size)
+{
+	IpcMemoryId shmid;
+	void	   *requestedAddress = NULL;
+	void	   *memAddress;
+
+	/*
+	 * Normally we just pass requestedAddress = NULL to shmat(), allowing the
+	 * system to choose where the segment gets mapped.  But in an EXEC_BACKEND
+	 * build, it's possible for whatever is chosen in the postmaster to not
+	 * work for backends, due to variations in address space layout.  As a
+	 * rather klugy workaround, allow the user to specify the address to use
+	 * via setting the environment variable PG_SHMEM_ADDR.  (If this were of
+	 * interest for anything except debugging, we'd probably create a cleaner
+	 * and better-documented way to set it, such as a GUC.)
+	 */
+#ifdef EXEC_BACKEND
+	{
+		char	   *pg_shmem_addr = getenv("PG_SHMEM_ADDR");
+
+		if (pg_shmem_addr)
+			requestedAddress = (void *) strtoul(pg_shmem_addr, NULL, 0);
+	}
+#endif
+
+	shmid = shmget(memKey, size, IPC_CREAT | IPC_EXCL | IPCProtection);
+
+	if (shmid < 0)
+	{
+		int			shmget_errno = errno;
+
+		/*
+		 * Fail quietly if error indicates a collision with existing segment.
+		 * One would expect EEXIST, given that we said IPC_EXCL, but perhaps
+		 * we could get a permission violation instead?  Also, EIDRM might
+		 * occur if an old seg is slated for destruction but not gone yet.
+		 */
+		if (shmget_errno == EEXIST || shmget_errno == EACCES
+#ifdef EIDRM
+			|| shmget_errno == EIDRM
+#endif
+			)
+			return NULL;
+
+		/*
+		 * Some BSD-derived kernels are known to return EINVAL, not EEXIST, if
+		 * there is an existing segment but it's smaller than "size" (this is
+		 * a result of poorly-thought-out ordering of error tests). To
+		 * distinguish between collision and invalid size in such cases, we
+		 * make a second try with size = 0.  These kernels do not test size
+		 * against SHMMIN in the preexisting-segment case, so we will not get
+		 * EINVAL a second time if there is such a segment.
+		 */
+		if (shmget_errno == EINVAL)
+		{
+			shmid = shmget(memKey, 0, IPC_CREAT | IPC_EXCL | IPCProtection);
+
+			if (shmid < 0)
+			{
+				/* As above, fail quietly if we verify a collision */
+				if (errno == EEXIST || errno == EACCES
+#ifdef EIDRM
+					|| errno == EIDRM
+#endif
+					)
+					return NULL;
+				/* Otherwise, fall through to report the original error */
+			}
+			else
+			{
+				/*
+				 * On most platforms we cannot get here because SHMMIN is
+				 * greater than zero.  However, if we do succeed in creating a
+				 * zero-size segment, free it and then fall through to report
+				 * the original error.
+				 */
+				if (shmctl(shmid, IPC_RMID, NULL) < 0)
+					elog(LOG, "shmctl(%d, %d, 0) failed: %m",
+						 (int) shmid, IPC_RMID);
+			}
+		}
+
+		/*
+		 * Else complain and abort.
+		 *
+		 * Note: at this point EINVAL should mean that either SHMMIN or SHMMAX
+		 * is violated.  SHMALL violation might be reported as either ENOMEM
+		 * (BSDen) or ENOSPC (Linux); the Single Unix Spec fails to say which
+		 * it should be.  SHMMNI violation is ENOSPC, per spec.  Just plain
+		 * not-enough-RAM is ENOMEM.
+		 */
+		errno = shmget_errno;
+		ereport(FATAL,
+				(errmsg("could not create shared memory segment: %m"),
+				 errdetail("Failed system call was shmget(key=%lu, size=%zu, 0%o).",
+						   (unsigned long) memKey, size,
+						   IPC_CREAT | IPC_EXCL | IPCProtection),
+				 (shmget_errno == EINVAL) ?
+				 errhint("This error usually means that PostgreSQL's request for a shared memory "
+						 "segment exceeded your kernel's SHMMAX parameter, or possibly that "
+						 "it is less than "
+						 "your kernel's SHMMIN parameter.\n"
+						 "The PostgreSQL documentation contains more information about shared "
+						 "memory configuration.") : 0,
+				 (shmget_errno == ENOMEM) ?
+				 errhint("This error usually means that PostgreSQL's request for a shared "
+						 "memory segment exceeded your kernel's SHMALL parameter.  You might need "
+						 "to reconfigure the kernel with larger SHMALL.\n"
+						 "The PostgreSQL documentation contains more information about shared "
+						 "memory configuration.") : 0,
+				 (shmget_errno == ENOSPC) ?
+				 errhint("This error does *not* mean that you have run out of disk space.  "
+						 "It occurs either if all available shared memory IDs have been taken, "
+						 "in which case you need to raise the SHMMNI parameter in your kernel, "
+						 "or because the system's overall limit for shared memory has been "
+						 "reached.\n"
+						 "The PostgreSQL documentation contains more information about shared "
+						 "memory configuration.") : 0));
+	}
+
+	/* Register on-exit routine to delete the new segment */
+	on_shmem_exit(IpcMemoryDelete, Int32GetDatum(shmid));
+
+	/* OK, should be able to attach to the segment */
+	memAddress = shmat(shmid, requestedAddress, PG_SHMAT_FLAGS);
+
+	if (memAddress == (void *) -1)
+		elog(FATAL, "shmat(id=%d, addr=%p, flags=0x%x) failed: %m",
+			 shmid, requestedAddress, PG_SHMAT_FLAGS);
+
+	/* Register on-exit routine to detach new segment before deleting */
+	on_shmem_exit(IpcMemoryDetach, PointerGetDatum(memAddress));
+
+	/*
+	 * Store shmem key and ID in data directory lockfile.  Format to try to
+	 * keep it the same length always (trailing junk in the lockfile won't
+	 * hurt, but might confuse humans).
+	 */
+	{
+		char		line[64];
+
+		sprintf(line, "%9lu %9lu",
+				(unsigned long) memKey, (unsigned long) shmid);
+		AddToDataDirLockFile(LOCK_FILE_LINE_SHMEM_KEY, line);
+	}
+
+	return memAddress;
+}
+
+/****************************************************************************/
+/*	IpcMemoryDetach(status, shmaddr)	removes a shared memory segment		*/
+/*										from process' address space			*/
+/*	(called as an on_shmem_exit callback, hence funny argument list)		*/
+/****************************************************************************/
+static void
+IpcMemoryDetach(int status, Datum shmaddr)
+{
+	/* Detach System V shared memory block. */
+	if (shmdt(DatumGetPointer(shmaddr)) < 0)
+		elog(LOG, "shmdt(%p) failed: %m", DatumGetPointer(shmaddr));
+}
+
+/****************************************************************************/
+/*	IpcMemoryDelete(status, shmId)		deletes a shared memory segment		*/
+/*	(called as an on_shmem_exit callback, hence funny argument list)		*/
+/****************************************************************************/
+static void
+IpcMemoryDelete(int status, Datum shmId)
+{
+	if (shmctl(DatumGetInt32(shmId), IPC_RMID, NULL) < 0)
+		elog(LOG, "shmctl(%d, %d, 0) failed: %m",
+			 DatumGetInt32(shmId), IPC_RMID);
+}
+
+/*
+ * PGSharedMemoryIsInUse
+ *
+ * Is a previously-existing shmem segment still existing and in use?
+ *
+ * The point of this exercise is to detect the case where a prior postmaster
+ * crashed, but it left child backends that are still running.  Therefore
+ * we only care about shmem segments that are associated with the intended
+ * DataDir.  This is an important consideration since accidental matches of
+ * shmem segment IDs are reasonably common.
+ */
+bool
+PGSharedMemoryIsInUse(unsigned long id1, unsigned long id2)
+{
+	PGShmemHeader *memAddress;
+	IpcMemoryState state;
+
+	state = PGSharedMemoryAttach((IpcMemoryId) id2, NULL, &memAddress);
+	if (memAddress && shmdt(memAddress) < 0)
+		elog(LOG, "shmdt(%p) failed: %m", memAddress);
+	switch (state)
+	{
+		case SHMSTATE_ENOENT:
+		case SHMSTATE_FOREIGN:
+		case SHMSTATE_UNATTACHED:
+			return false;
+		case SHMSTATE_ANALYSIS_FAILURE:
+		case SHMSTATE_ATTACHED:
+			return true;
+	}
+	return true;
+}
+
+/*
+ * Test for a segment with id shmId; see comment at IpcMemoryState.
+ *
+ * If the segment exists, we'll attempt to attach to it, using attachAt
+ * if that's not NULL (but it's best to pass NULL if possible).
+ *
+ * *addr is set to the segment memory address if we attached to it, else NULL.
+ */
+static IpcMemoryState
+PGSharedMemoryAttach(IpcMemoryId shmId,
+					 void *attachAt,
+					 PGShmemHeader **addr)
+{
+	struct shmid_ds shmStat;
+	struct stat statbuf;
+	PGShmemHeader *hdr;
+
+	*addr = NULL;
+
+	/*
+	 * First, try to stat the shm segment ID, to see if it exists at all.
+	 */
+	if (shmctl(shmId, IPC_STAT, &shmStat) < 0)
+	{
+		/*
+		 * EINVAL actually has multiple possible causes documented in the
+		 * shmctl man page, but we assume it must mean the segment no longer
+		 * exists.
+		 */
+		if (errno == EINVAL)
+			return SHMSTATE_ENOENT;
+
+		/*
+		 * EACCES implies we have no read permission, which means it is not a
+		 * Postgres shmem segment (or at least, not one that is relevant to
+		 * our data directory).
+		 */
+		if (errno == EACCES)
+			return SHMSTATE_FOREIGN;
+
+		/*
+		 * Some Linux kernel versions (in fact, all of them as of July 2007)
+		 * sometimes return EIDRM when EINVAL is correct.  The Linux kernel
+		 * actually does not have any internal state that would justify
+		 * returning EIDRM, so we can get away with assuming that EIDRM is
+		 * equivalent to EINVAL on that platform.
+		 */
+#ifdef HAVE_LINUX_EIDRM_BUG
+		if (errno == EIDRM)
+			return SHMSTATE_ENOENT;
+#endif
+
+		/*
+		 * Otherwise, we had better assume that the segment is in use.  The
+		 * only likely case is (non-Linux, assumed spec-compliant) EIDRM,
+		 * which implies that the segment has been IPC_RMID'd but there are
+		 * still processes attached to it.
+		 */
+		return SHMSTATE_ANALYSIS_FAILURE;
+	}
+
+	/*
+	 * Try to attach to the segment and see if it matches our data directory.
+	 * This avoids any risk of duplicate-shmem-key conflicts on machines that
+	 * are running several postmasters under the same userid.
+	 *
+	 * (When we're called from PGSharedMemoryCreate, this stat call is
+	 * duplicative; but since this isn't a high-traffic case it's not worth
+	 * trying to optimize.)
+	 */
+	if (stat(DataDir, &statbuf) < 0)
+		return SHMSTATE_ANALYSIS_FAILURE;	/* can't stat; be conservative */
+
+	hdr = (PGShmemHeader *) shmat(shmId, attachAt, PG_SHMAT_FLAGS);
+	if (hdr == (PGShmemHeader *) -1)
+	{
+		/*
+		 * Attachment failed.  The cases we're interested in are the same as
+		 * for the shmctl() call above.  In particular, note that the owning
+		 * postmaster could have terminated and removed the segment between
+		 * shmctl() and shmat().
+		 *
+		 * If attachAt isn't NULL, it's possible that EINVAL reflects a
+		 * problem with that address not a vanished segment, so it's best to
+		 * pass NULL when probing for conflicting segments.
+		 */
+		if (errno == EINVAL)
+			return SHMSTATE_ENOENT; /* segment disappeared */
+		if (errno == EACCES)
+			return SHMSTATE_FOREIGN;	/* must be non-Postgres */
+#ifdef HAVE_LINUX_EIDRM_BUG
+		if (errno == EIDRM)
+			return SHMSTATE_ENOENT; /* segment disappeared */
+#endif
+		/* Otherwise, be conservative. */
+		return SHMSTATE_ANALYSIS_FAILURE;
+	}
+	*addr = hdr;
+
+	if (hdr->magic != PGShmemMagic ||
+		hdr->device != statbuf.st_dev ||
+		hdr->inode != statbuf.st_ino)
+	{
+		/*
+		 * It's either not a Postgres segment, or not one for my data
+		 * directory.
+		 */
+		return SHMSTATE_FOREIGN;
+	}
+
+	/*
+	 * It does match our data directory, so now test whether any processes are
+	 * still attached to it.  (We are, now, but the shm_nattch result is from
+	 * before we attached to it.)
+	 */
+	return shmStat.shm_nattch == 0 ? SHMSTATE_UNATTACHED : SHMSTATE_ATTACHED;
+}
+
+#ifdef MAP_HUGETLB
+
+/*
+ * Identify the huge page size to use.
+ *
+ * Some Linux kernel versions have a bug causing mmap() to fail on requests
+ * that are not a multiple of the hugepage size.  Versions without that bug
+ * instead silently round the request up to the next hugepage multiple ---
+ * and then munmap() fails when we give it a size different from that.
+ * So we have to round our request up to a multiple of the actual hugepage
+ * size to avoid trouble.
+ *
+ * Doing the round-up ourselves also lets us make use of the extra memory,
+ * rather than just wasting it.  Currently, we just increase the available
+ * space recorded in the shmem header, which will make the extra usable for
+ * purposes such as additional locktable entries.  Someday, for very large
+ * hugepage sizes, we might want to think about more invasive strategies,
+ * such as increasing shared_buffers to absorb the extra space.
+ *
+ * Returns the (real or assumed) page size into *hugepagesize,
+ * and the hugepage-related mmap flags to use into *mmap_flags.
+ *
+ * Currently *mmap_flags is always just MAP_HUGETLB.  Someday, on systems
+ * that support it, we might OR in additional bits to specify a particular
+ * non-default huge page size.
+ */
+static void
+GetHugePageSize(Size *hugepagesize, int *mmap_flags)
+{
+	/*
+	 * If we fail to find out the system's default huge page size, assume it
+	 * is 2MB.  This will work fine when the actual size is less.  If it's
+	 * more, we might get mmap() or munmap() failures due to unaligned
+	 * requests; but at this writing, there are no reports of any non-Linux
+	 * systems being picky about that.
+	 */
+	*hugepagesize = 2 * 1024 * 1024;
+	*mmap_flags = MAP_HUGETLB;
+
+	/*
+	 * System-dependent code to find out the default huge page size.
+	 *
+	 * On Linux, read /proc/meminfo looking for a line like "Hugepagesize:
+	 * nnnn kB".  Ignore any failures, falling back to the preset default.
+	 */
+#ifdef __linux__
+	{
+		FILE	   *fp = AllocateFile("/proc/meminfo", "r");
+		char		buf[128];
+		unsigned int sz;
+		char		ch;
+
+		if (fp)
+		{
+			while (fgets(buf, sizeof(buf), fp))
+			{
+				if (sscanf(buf, "Hugepagesize: %u %c", &sz, &ch) == 2)
+				{
+					if (ch == 'k')
+					{
+						*hugepagesize = sz * (Size) 1024;
+						break;
+					}
+					/* We could accept other units besides kB, if needed */
+				}
+			}
+			FreeFile(fp);
+		}
+	}
+#endif							/* __linux__ */
+}
+
+#endif							/* MAP_HUGETLB */
+
+/*
+ * Creates an anonymous mmap()ed shared memory segment.
+ *
+ * Pass the requested size in *size.  This function will modify *size to the
+ * actual size of the allocation, if it ends up allocating a segment that is
+ * larger than requested.
+ */
+static void *
+CreateAnonymousSegment(Size *size)
+{
+	Size		allocsize = *size;
+	void	   *ptr = MAP_FAILED;
+	int			mmap_errno = 0;
+
+#ifndef MAP_HUGETLB
+	/* PGSharedMemoryCreate should have dealt with this case */
+	Assert(huge_pages != HUGE_PAGES_ON);
+#else
+	if (huge_pages == HUGE_PAGES_ON || huge_pages == HUGE_PAGES_TRY)
+	{
+		/*
+		 * Round up the request size to a suitable large value.
+		 */
+		Size		hugepagesize;
+		int			mmap_flags;
+
+		GetHugePageSize(&hugepagesize, &mmap_flags);
+
+		if (allocsize % hugepagesize != 0)
+			allocsize += hugepagesize - (allocsize % hugepagesize);
+
+		ptr = mmap(NULL, allocsize, PROT_READ | PROT_WRITE,
+				   PG_MMAP_FLAGS | mmap_flags, -1, 0);
+		mmap_errno = errno;
+		if (huge_pages == HUGE_PAGES_TRY && ptr == MAP_FAILED)
+			elog(DEBUG1, "mmap(%zu) with MAP_HUGETLB failed, huge pages disabled: %m",
+				 allocsize);
+	}
+#endif
+
+	if (ptr == MAP_FAILED && huge_pages != HUGE_PAGES_ON)
+	{
+		/*
+		 * Use the original size, not the rounded-up value, when falling back
+		 * to non-huge pages.
+		 */
+		allocsize = *size;
+		ptr = mmap(NULL, allocsize, PROT_READ | PROT_WRITE,
+				   PG_MMAP_FLAGS, -1, 0);
+		mmap_errno = errno;
+	}
+
+	if (ptr == MAP_FAILED)
+	{
+		errno = mmap_errno;
+		ereport(FATAL,
+				(errmsg("could not map anonymous shared memory: %m"),
+				 (mmap_errno == ENOMEM) ?
+				 errhint("This error usually means that PostgreSQL's request "
+						 "for a shared memory segment exceeded available memory, "
+						 "swap space, or huge pages. To reduce the request size "
+						 "(currently %zu bytes), reduce PostgreSQL's shared "
+						 "memory usage, perhaps by reducing shared_buffers or "
+						 "max_connections.",
+						 *size) : 0));
+	}
+
+	*size = allocsize;
+	return ptr;
+}
+
+/*
+ * AnonymousShmemDetach --- detach from an anonymous mmap'd block
+ * (called as an on_shmem_exit callback, hence funny argument list)
+ */
+static void
+AnonymousShmemDetach(int status, Datum arg)
+{
+	/* Release anonymous shared memory block, if any. */
+	if (AnonymousShmem != NULL)
+	{
+		if (munmap(AnonymousShmem, AnonymousShmemSize) < 0)
+			elog(LOG, "munmap(%p, %zu) failed: %m",
+				 AnonymousShmem, AnonymousShmemSize);
+		AnonymousShmem = NULL;
+	}
+}
+
+/*
+ * PGSharedMemoryCreate
+ *
+ * Create a shared memory segment of the given size and initialize its
+ * standard header.  Also, register an on_shmem_exit callback to release
+ * the storage.
+ *
+ * Dead Postgres segments pertinent to this DataDir are recycled if found, but
+ * we do not fail upon collision with foreign shmem segments.  The idea here
+ * is to detect and re-use keys that may have been assigned by a crashed
+ * postmaster or backend.
+ */
+PGShmemHeader *
+PGSharedMemoryCreate(Size size,
+					 PGShmemHeader **shim)
+{
+	IpcMemoryKey NextShmemSegID;
+	void	   *memAddress;
+	PGShmemHeader *hdr;
+	struct stat statbuf;
+	Size		sysvsize;
+
+	/*
+	 * We use the data directory's ID info (inode and device numbers) to
+	 * positively identify shmem segments associated with this data dir, and
+	 * also as seeds for searching for a free shmem key.
+	 */
+	if (stat(DataDir, &statbuf) < 0)
+		ereport(FATAL,
+				(errcode_for_file_access(),
+				 errmsg("could not stat data directory \"%s\": %m",
+						DataDir)));
+
+	/* Complain if hugepages demanded but we can't possibly support them */
+#if !defined(MAP_HUGETLB)
+	if (huge_pages == HUGE_PAGES_ON)
+		ereport(ERROR,
+				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+				 errmsg("huge pages not supported on this platform")));
+#endif
+
+	/* Room for a header? */
+	Assert(size > MAXALIGN(sizeof(PGShmemHeader)));
+
+	if (shared_memory_type == SHMEM_TYPE_MMAP)
+	{
+		AnonymousShmem = CreateAnonymousSegment(&size);
+		AnonymousShmemSize = size;
+
+		/* Register on-exit routine to unmap the anonymous segment */
+		on_shmem_exit(AnonymousShmemDetach, (Datum) 0);
+
+		/* Now we need only allocate a minimal-sized SysV shmem block. */
+		sysvsize = sizeof(PGShmemHeader);
+	}
+	else
+		sysvsize = size;
+
+	/*
+	 * Loop till we find a free IPC key.  Trust CreateDataDirLockFile() to
+	 * ensure no more than one postmaster per data directory can enter this
+	 * loop simultaneously.  (CreateDataDirLockFile() does not entirely ensure
+	 * that, but prefer fixing it over coping here.)
+	 */
+	NextShmemSegID = statbuf.st_ino;
+
+	for (;;)
+	{
+		IpcMemoryId shmid;
+		PGShmemHeader *oldhdr;
+		IpcMemoryState state;
+
+		/* Try to create new segment */
+		memAddress = InternalIpcMemoryCreate(NextShmemSegID, sysvsize);
+		if (memAddress)
+			break;				/* successful create and attach */
+
+		/* Check shared memory and possibly remove and recreate */
+
+		/*
+		 * shmget() failure is typically EACCES, hence SHMSTATE_FOREIGN.
+		 * ENOENT, a narrow possibility, implies SHMSTATE_ENOENT, but one can
+		 * safely treat SHMSTATE_ENOENT like SHMSTATE_FOREIGN.
+		 */
+		shmid = shmget(NextShmemSegID, sizeof(PGShmemHeader), 0);
+		if (shmid < 0)
+		{
+			oldhdr = NULL;
+			state = SHMSTATE_FOREIGN;
+		}
+		else
+			state = PGSharedMemoryAttach(shmid, NULL, &oldhdr);
+
+		switch (state)
+		{
+			case SHMSTATE_ANALYSIS_FAILURE:
+			case SHMSTATE_ATTACHED:
+				ereport(FATAL,
+						(errcode(ERRCODE_LOCK_FILE_EXISTS),
+						 errmsg("pre-existing shared memory block (key %lu, ID %lu) is still in use",
+								(unsigned long) NextShmemSegID,
+								(unsigned long) shmid),
+						 errhint("Terminate any old server processes associated with data directory \"%s\".",
+								 DataDir)));
+				break;
+			case SHMSTATE_ENOENT:
+
+				/*
+				 * To our surprise, some other process deleted since our last
+				 * InternalIpcMemoryCreate().  Moments earlier, we would have
+				 * seen SHMSTATE_FOREIGN.  Try that same ID again.
+				 */
+				elog(LOG,
+					 "shared memory block (key %lu, ID %lu) deleted during startup",
+					 (unsigned long) NextShmemSegID,
+					 (unsigned long) shmid);
+				break;
+			case SHMSTATE_FOREIGN:
+				NextShmemSegID++;
+				break;
+			case SHMSTATE_UNATTACHED:
+
+				/*
+				 * The segment pertains to DataDir, and every process that had
+				 * used it has died or detached.  Zap it, if possible, and any
+				 * associated dynamic shared memory segments, as well.  This
+				 * shouldn't fail, but if it does, assume the segment belongs
+				 * to someone else after all, and try the next candidate.
+				 * Otherwise, try again to create the segment.  That may fail
+				 * if some other process creates the same shmem key before we
+				 * do, in which case we'll try the next key.
+				 */
+				if (oldhdr->dsm_control != 0)
+					dsm_cleanup_using_control_segment(oldhdr->dsm_control);
+				if (shmctl(shmid, IPC_RMID, NULL) < 0)
+					NextShmemSegID++;
+				break;
+		}
+
+		if (oldhdr && shmdt(oldhdr) < 0)
+			elog(LOG, "shmdt(%p) failed: %m", oldhdr);
+	}
+
+	/* Initialize new segment. */
+	hdr = (PGShmemHeader *) memAddress;
+	hdr->creatorPID = getpid();
+	hdr->magic = PGShmemMagic;
+	hdr->dsm_control = 0;
+
+	/* Fill in the data directory ID info, too */
+	hdr->device = statbuf.st_dev;
+	hdr->inode = statbuf.st_ino;
+
+	/*
+	 * Initialize space allocation status for segment.
+	 */
+	hdr->totalsize = size;
+	hdr->freeoffset = MAXALIGN(sizeof(PGShmemHeader));
+	*shim = hdr;
+
+	/* Save info for possible future use */
+	UsedShmemSegAddr = memAddress;
+	UsedShmemSegID = (unsigned long) NextShmemSegID;
+
+	/*
+	 * If AnonymousShmem is NULL here, then we're not using anonymous shared
+	 * memory, and should return a pointer to the System V shared memory
+	 * block. Otherwise, the System V shared memory block is only a shim, and
+	 * we must return a pointer to the real block.
+	 */
+	if (AnonymousShmem == NULL)
+		return hdr;
+	memcpy(AnonymousShmem, hdr, sizeof(PGShmemHeader));
+	return (PGShmemHeader *) AnonymousShmem;
+}
+
+#ifdef EXEC_BACKEND
+
+/*
+ * PGSharedMemoryReAttach
+ *
+ * This is called during startup of a postmaster child process to re-attach to
+ * an already existing shared memory segment.  This is needed only in the
+ * EXEC_BACKEND case; otherwise postmaster children inherit the shared memory
+ * segment attachment via fork().
+ *
+ * UsedShmemSegID and UsedShmemSegAddr are implicit parameters to this
+ * routine.  The caller must have already restored them to the postmaster's
+ * values.
+ */
+void
+PGSharedMemoryReAttach(void)
+{
+	IpcMemoryId shmid;
+	PGShmemHeader *hdr;
+	IpcMemoryState state;
+	void	   *origUsedShmemSegAddr = UsedShmemSegAddr;
+
+	Assert(UsedShmemSegAddr != NULL);
+	Assert(IsUnderPostmaster);
+
+#ifdef __CYGWIN__
+	/* cygipc (currently) appears to not detach on exec. */
+	PGSharedMemoryDetach();
+	UsedShmemSegAddr = origUsedShmemSegAddr;
+#endif
+
+	elog(DEBUG3, "attaching to %p", UsedShmemSegAddr);
+	shmid = shmget(UsedShmemSegID, sizeof(PGShmemHeader), 0);
+	if (shmid < 0)
+		state = SHMSTATE_FOREIGN;
+	else
+		state = PGSharedMemoryAttach(shmid, UsedShmemSegAddr, &hdr);
+	if (state != SHMSTATE_ATTACHED)
+		elog(FATAL, "could not reattach to shared memory (key=%d, addr=%p): %m",
+			 (int) UsedShmemSegID, UsedShmemSegAddr);
+	if (hdr != origUsedShmemSegAddr)
+		elog(FATAL, "reattaching to shared memory returned unexpected address (got %p, expected %p)",
+			 hdr, origUsedShmemSegAddr);
+	dsm_set_control_handle(hdr->dsm_control);
+
+	UsedShmemSegAddr = hdr;		/* probably redundant */
+}
+
+/*
+ * PGSharedMemoryNoReAttach
+ *
+ * This is called during startup of a postmaster child process when we choose
+ * *not* to re-attach to the existing shared memory segment.  We must clean up
+ * to leave things in the appropriate state.  This is not used in the non
+ * EXEC_BACKEND case, either.
+ *
+ * The child process startup logic might or might not call PGSharedMemoryDetach
+ * after this; make sure that it will be a no-op if called.
+ *
+ * UsedShmemSegID and UsedShmemSegAddr are implicit parameters to this
+ * routine.  The caller must have already restored them to the postmaster's
+ * values.
+ */
+void
+PGSharedMemoryNoReAttach(void)
+{
+	Assert(UsedShmemSegAddr != NULL);
+	Assert(IsUnderPostmaster);
+
+#ifdef __CYGWIN__
+	/* cygipc (currently) appears to not detach on exec. */
+	PGSharedMemoryDetach();
+#endif
+
+	/* For cleanliness, reset UsedShmemSegAddr to show we're not attached. */
+	UsedShmemSegAddr = NULL;
+	/* And the same for UsedShmemSegID. */
+	UsedShmemSegID = 0;
+}
+
+#endif							/* EXEC_BACKEND */
+
+/*
+ * PGSharedMemoryDetach
+ *
+ * Detach from the shared memory segment, if still attached.  This is not
+ * intended to be called explicitly by the process that originally created the
+ * segment (it will have on_shmem_exit callback(s) registered to do that).
+ * Rather, this is for subprocesses that have inherited an attachment and want
+ * to get rid of it.
+ *
+ * UsedShmemSegID and UsedShmemSegAddr are implicit parameters to this
+ * routine, also AnonymousShmem and AnonymousShmemSize.
+ */
+void
+PGSharedMemoryDetach(void)
+{
+	if (UsedShmemSegAddr != NULL)
+	{
+		if ((shmdt(UsedShmemSegAddr) < 0)
+#if defined(EXEC_BACKEND) && defined(__CYGWIN__)
+		/* Work-around for cygipc exec bug */
+			&& shmdt(NULL) < 0
+#endif
+			)
+			elog(LOG, "shmdt(%p) failed: %m", UsedShmemSegAddr);
+		UsedShmemSegAddr = NULL;
+	}
+
+	if (AnonymousShmem != NULL)
+	{
+		if (munmap(AnonymousShmem, AnonymousShmemSize) < 0)
+			elog(LOG, "munmap(%p, %zu) failed: %m",
+				 AnonymousShmem, AnonymousShmemSize);
+		AnonymousShmem = NULL;
+	}
+}
diff --git a/src/backend/port/tas/dummy.s b/src/backend/port/tas/dummy.s
new file mode 100644
index 0000000..e69de29
--- /dev/null
+++ b/src/backend/port/tas/dummy.s
diff --git a/src/backend/port/tas/hpux_hppa.s b/src/backend/port/tas/hpux_hppa.s
new file mode 100644
index 0000000..d978a7c
--- /dev/null
+++ b/src/backend/port/tas/hpux_hppa.s
@@ -0,0 +1,28 @@
+
+        .SPACE  $TEXT$,SORT=8
+        .SUBSPA $CODE$,QUAD=0,ALIGN=4,ACCESS=44,CODE_ONLY,SORT=24
+tas
+        .PROC
+        .CALLINFO CALLER,FRAME=0,ENTRY_SR=3
+        .ENTRY
+        LDO     15(%r26),%r31   ;offset 0x0
+        DEPI    0,31,4,%r31     ;offset 0x4
+        LDCWX   0(0,%r31),%r23  ;offset 0x8
+        COMICLR,=       0,%r23,%r0      ;offset 0xc
+        DEP,TR  %r0,31,32,%r28  ;offset 0x10
+$00000001
+        LDI     1,%r28  ;offset 0x14
+$L0
+        .EXIT
+        BV,N    %r0(%r2)        ;offset 0x18
+        .PROCEND ;in=26;out=28;
+
+
+        .SPACE  $TEXT$
+        .SUBSPA $CODE$
+        .SPACE  $PRIVATE$,SORT=16
+        .SUBSPA $DATA$,QUAD=1,ALIGN=8,ACCESS=31,SORT=16
+        .SPACE  $TEXT$
+        .SUBSPA $CODE$
+        .EXPORT tas,ENTRY,PRIV_LEV=3,ARGW0=GR,RTNVAL=GR
+        .END
diff --git a/src/backend/port/tas/sunstudio_sparc.s b/src/backend/port/tas/sunstudio_sparc.s
new file mode 100644
index 0000000..4bebf07
--- /dev/null
+++ b/src/backend/port/tas/sunstudio_sparc.s
@@ -0,0 +1,53 @@
+!-------------------------------------------------------------------------
+!
+! sunstudio_sparc.s
+!	  compare and swap for Sun Studio on Sparc
+!
+! Portions Copyright (c) 1996-2020, PostgreSQL Global Development Group
+! Portions Copyright (c) 1994, Regents of the University of California
+!
+! IDENTIFICATION
+!	  src/backend/port/tas/sunstudio_sparc.s
+!
+!-------------------------------------------------------------------------
+
+! Fortunately the Sun compiler can process cpp conditionals with -P
+
+! '/' is the comment for x86, while '!' is the comment for Sparc
+
+#if defined(__sparcv9) || defined(__sparc)
+
+	.section        ".text"
+	.align  8
+	.skip   24
+	.align  4
+
+	.global pg_atomic_cas
+pg_atomic_cas:
+
+	! "cas" only works on sparcv9 and sparcv8plus chips, and
+	! requires a compiler targeting these CPUs.  It will fail
+	! on a compiler targeting sparcv8, and of course will not
+	! be understood by a sparcv8 CPU.  gcc continues to use
+	! "ldstub" because it targets sparcv7.
+	!
+	! There is actually a trick for embedding "cas" in a
+	! sparcv8-targeted compiler, but it can only be run
+	! on a sparcv8plus/v9 cpus:
+	!
+	!   http://cvs.opensolaris.org/source/xref/on/usr/src/lib/libc/sparc/threads/sparc.il
+	!
+	! NB: We're assuming we're running on a TSO system here - solaris
+	! userland luckily always has done so.
+
+#if defined(__sparcv9) || defined(__sparcv8plus)
+	cas     [%o0],%o2,%o1
+#else
+	ldstub [%o0],%o1
+#endif
+	mov     %o1,%o0
+	retl
+	nop
+	.type   pg_atomic_cas,2
+	.size   pg_atomic_cas,(.-pg_atomic_cas)
+#endif
diff --git a/src/backend/port/tas/sunstudio_x86.s b/src/backend/port/tas/sunstudio_x86.s
new file mode 100644
index 0000000..d95e173
--- /dev/null
+++ b/src/backend/port/tas/sunstudio_x86.s
@@ -0,0 +1,43 @@
+/-------------------------------------------------------------------------
+/
+/ sunstudio_x86.s
+/	  compare and swap for Sun Studio on x86
+/
+/ Portions Copyright (c) 1996-2020, PostgreSQL Global Development Group
+/ Portions Copyright (c) 1994, Regents of the University of California
+/
+/ IDENTIFICATION
+/	  src/backend/port/tas/sunstudio_x86.s
+/
+/-------------------------------------------------------------------------
+
+/ Fortunately the Sun compiler can process cpp conditionals with -P
+
+/ '/' is the comment for x86, while '!' is the comment for Sparc
+
+	.file   "tas.s"
+
+#if defined(__amd64)
+	.code64
+#endif
+
+	.globl pg_atomic_cas
+	.type pg_atomic_cas, @function
+
+	.section .text, "ax"
+	.align 16
+
+pg_atomic_cas:
+#if defined(__amd64)
+	movl       %edx,%eax
+	lock
+	cmpxchgl   %esi,(%rdi)
+#else
+	movl    4(%esp), %edx
+	movl    8(%esp), %ecx
+	movl    12(%esp), %eax
+	lock
+	cmpxchgl %ecx, (%edx)
+#endif
+	ret
+	.size pg_atomic_cas, . - pg_atomic_cas
diff --git a/src/backend/port/win32/Makefile b/src/backend/port/win32/Makefile
new file mode 100644
index 0000000..90126f6
--- /dev/null
+++ b/src/backend/port/win32/Makefile
@@ -0,0 +1,23 @@
+#-------------------------------------------------------------------------
+#
+# Makefile--
+#    Makefile for backend/port/win32
+#
+# IDENTIFICATION
+#    src/backend/port/win32/Makefile
+#
+#-------------------------------------------------------------------------
+
+subdir = src/backend/port/win32
+top_builddir = ../../../..
+include $(top_builddir)/src/Makefile.global
+
+OBJS = \
+	signal.o \
+	socket.o \
+	timer.o
+ifeq ($(have_win32_dbghelp), yes)
+OBJS += crashdump.o
+endif
+
+include $(top_srcdir)/src/backend/common.mk
diff --git a/src/backend/port/win32/crashdump.c b/src/backend/port/win32/crashdump.c
new file mode 100644
index 0000000..e6c6837
--- /dev/null
+++ b/src/backend/port/win32/crashdump.c
@@ -0,0 +1,183 @@
+/*-------------------------------------------------------------------------
+ *
+ * crashdump.c
+ *		   Automatic crash dump creation for PostgreSQL on Windows
+ *
+ * The crashdump feature traps unhandled win32 exceptions produced by the
+ * backend, and tries to produce a Windows MiniDump crash
+ * dump for later debugging and analysis. The machine performing the dump
+ * doesn't need any special debugging tools; the user only needs to send
+ * the dump to somebody who has the same version of PostgreSQL and has debugging
+ * tools.
+ *
+ * crashdump module originally by Craig Ringer <ringerc@ringerc.id.au>
+ *
+ * LIMITATIONS
+ * ===========
+ * This *won't* work in hard OOM situations or stack overflows.
+ *
+ * For those, it'd be necessary to take a much more complicated approach where
+ * the handler switches to a new stack (if it can) and forks a helper process
+ * to debug it self.
+ *
+ * POSSIBLE FUTURE WORK
+ * ====================
+ * For bonus points, the crash dump format permits embedding of user-supplied
+ * data. If there's anything else that should always be supplied with a crash
+ * dump (postgresql.conf? Last few lines of a log file?), it could potentially
+ * be added, though at the cost of a greater chance of the crash dump failing.
+ *
+ *
+ * Portions Copyright (c) 1996-2020, PostgreSQL Global Development Group
+ *
+ * IDENTIFICATION
+ *	  src/backend/port/win32/crashdump.c
+ *
+ *-------------------------------------------------------------------------
+ */
+
+#include "postgres.h"
+
+#define WIN32_LEAN_AND_MEAN
+
+/*
+ * Some versions of the MS SDK contain "typedef enum { ... } ;" which the MS
+ * compiler quite sanely complains about. Well done, Microsoft.
+ * This pragma disables the warning just while we include the header.
+ * The pragma is known to work with all (as at the time of writing) supported
+ * versions of MSVC.
+ */
+#ifdef _MSC_VER
+#pragma warning(push)
+#pragma warning(disable : 4091)
+#endif
+#include <dbghelp.h>
+#ifdef _MSC_VER
+#pragma warning(pop)
+#endif
+
+/*
+ * Much of the following code is based on CodeProject and MSDN examples,
+ * particularly
+ * http://www.codeproject.com/KB/debug/postmortemdebug_standalone1.aspx
+ *
+ * Useful MSDN articles:
+ *
+ * http://msdn.microsoft.com/en-us/library/ff805116(v=VS.85).aspx
+ * http://msdn.microsoft.com/en-us/library/ms679294(VS.85).aspx
+ *
+ * Other useful articles on working with minidumps:
+ * http://www.debuginfo.com/articles/effminidumps.html
+ */
+
+typedef BOOL (WINAPI * MINIDUMPWRITEDUMP) (HANDLE hProcess, DWORD dwPid, HANDLE hFile, MINIDUMP_TYPE DumpType,
+										   CONST PMINIDUMP_EXCEPTION_INFORMATION ExceptionParam,
+										   CONST PMINIDUMP_USER_STREAM_INFORMATION UserStreamParam,
+										   CONST PMINIDUMP_CALLBACK_INFORMATION CallbackParam
+);
+
+
+/*
+ * This function is the exception handler passed to SetUnhandledExceptionFilter.
+ * It's invoked only if there's an unhandled exception. The handler will use
+ * dbghelp.dll to generate a crash dump, then resume the normal unhandled
+ * exception process, which will generally exit with an error message from
+ * the runtime.
+ *
+ * This function is run under the unhandled exception handler, effectively
+ * in a crash context, so it should be careful with memory and avoid using
+ * any PostgreSQL functions.
+ */
+static LONG WINAPI
+crashDumpHandler(struct _EXCEPTION_POINTERS *pExceptionInfo)
+{
+	/*
+	 * We only write crash dumps if the "crashdumps" directory within the
+	 * postgres data directory exists.
+	 */
+	DWORD		attribs = GetFileAttributesA("crashdumps");
+
+	if (attribs != INVALID_FILE_ATTRIBUTES && (attribs & FILE_ATTRIBUTE_DIRECTORY))
+	{
+		/* 'crashdumps' exists and is a directory. Try to write a dump' */
+		HMODULE		hDll = NULL;
+		MINIDUMPWRITEDUMP pDump = NULL;
+		MINIDUMP_TYPE dumpType;
+		char		dumpPath[_MAX_PATH];
+		HANDLE		selfProcHandle = GetCurrentProcess();
+		DWORD		selfPid = GetProcessId(selfProcHandle);
+		HANDLE		dumpFile;
+		DWORD		systemTicks;
+		struct _MINIDUMP_EXCEPTION_INFORMATION ExInfo;
+
+		ExInfo.ThreadId = GetCurrentThreadId();
+		ExInfo.ExceptionPointers = pExceptionInfo;
+		ExInfo.ClientPointers = FALSE;
+
+		/* Load the dbghelp.dll library and functions */
+		hDll = LoadLibrary("dbghelp.dll");
+		if (hDll == NULL)
+		{
+			write_stderr("could not load dbghelp.dll, cannot write crash dump\n");
+			return EXCEPTION_CONTINUE_SEARCH;
+		}
+
+		pDump = (MINIDUMPWRITEDUMP) GetProcAddress(hDll, "MiniDumpWriteDump");
+
+		if (pDump == NULL)
+		{
+			write_stderr("could not load required functions in dbghelp.dll, cannot write crash dump\n");
+			return EXCEPTION_CONTINUE_SEARCH;
+		}
+
+		/*
+		 * Dump as much as we can, except shared memory, code segments, and
+		 * memory mapped files. Exactly what we can dump depends on the
+		 * version of dbghelp.dll, see:
+		 * http://msdn.microsoft.com/en-us/library/ms680519(v=VS.85).aspx
+		 */
+		dumpType = MiniDumpNormal | MiniDumpWithHandleData |
+			MiniDumpWithDataSegs;
+
+		if (GetProcAddress(hDll, "EnumDirTree") != NULL)
+		{
+			/* If this function exists, we have version 5.2 or newer */
+			dumpType |= MiniDumpWithIndirectlyReferencedMemory |
+				MiniDumpWithPrivateReadWriteMemory;
+		}
+
+		systemTicks = GetTickCount();
+		snprintf(dumpPath, _MAX_PATH,
+				 "crashdumps\\postgres-pid%0i-%0i.mdmp",
+				 (int) selfPid, (int) systemTicks);
+		dumpPath[_MAX_PATH - 1] = '\0';
+
+		dumpFile = CreateFile(dumpPath, GENERIC_WRITE, FILE_SHARE_WRITE,
+							  NULL, CREATE_ALWAYS, FILE_ATTRIBUTE_NORMAL,
+							  NULL);
+		if (dumpFile == INVALID_HANDLE_VALUE)
+		{
+			write_stderr("could not open crash dump file \"%s\" for writing: error code %lu\n",
+						 dumpPath, GetLastError());
+			return EXCEPTION_CONTINUE_SEARCH;
+		}
+
+		if ((*pDump) (selfProcHandle, selfPid, dumpFile, dumpType, &ExInfo,
+					  NULL, NULL))
+			write_stderr("wrote crash dump to file \"%s\"\n", dumpPath);
+		else
+			write_stderr("could not write crash dump to file \"%s\": error code %lu\n",
+						 dumpPath, GetLastError());
+
+		CloseHandle(dumpFile);
+	}
+
+	return EXCEPTION_CONTINUE_SEARCH;
+}
+
+
+void
+pgwin32_install_crashdump_handler(void)
+{
+	SetUnhandledExceptionFilter(crashDumpHandler);
+}
diff --git a/src/backend/port/win32/signal.c b/src/backend/port/win32/signal.c
new file mode 100644
index 0000000..3218b38
--- /dev/null
+++ b/src/backend/port/win32/signal.c
@@ -0,0 +1,344 @@
+/*-------------------------------------------------------------------------
+ *
+ * signal.c
+ *	  Microsoft Windows Win32 Signal Emulation Functions
+ *
+ * Portions Copyright (c) 1996-2020, PostgreSQL Global Development Group
+ *
+ * IDENTIFICATION
+ *	  src/backend/port/win32/signal.c
+ *
+ *-------------------------------------------------------------------------
+ */
+
+#include "postgres.h"
+
+#include "libpq/pqsignal.h"
+
+/*
+ * These are exported for use by the UNBLOCKED_SIGNAL_QUEUE() macro.
+ * pg_signal_queue must be volatile since it is changed by the signal
+ * handling thread and inspected without any lock by the main thread.
+ * pg_signal_mask is only changed by main thread so shouldn't need it.
+ */
+volatile int pg_signal_queue;
+int			pg_signal_mask;
+
+HANDLE		pgwin32_signal_event;
+HANDLE		pgwin32_initial_signal_pipe = INVALID_HANDLE_VALUE;
+
+/*
+ * pg_signal_crit_sec is used to protect only pg_signal_queue. That is the only
+ * variable that can be accessed from the signal sending threads!
+ */
+static CRITICAL_SECTION pg_signal_crit_sec;
+
+/* Note that array elements 0 are unused since they correspond to signal 0 */
+static pqsigfunc pg_signal_array[PG_SIGNAL_COUNT];
+static pqsigfunc pg_signal_defaults[PG_SIGNAL_COUNT];
+
+
+/* Signal handling thread functions */
+static DWORD WINAPI pg_signal_thread(LPVOID param);
+static BOOL WINAPI pg_console_handler(DWORD dwCtrlType);
+
+
+/*
+ * pg_usleep --- delay the specified number of microseconds, but
+ * stop waiting if a signal arrives.
+ *
+ * This replaces the non-signal-aware version provided by src/port/pgsleep.c.
+ */
+void
+pg_usleep(long microsec)
+{
+	Assert(pgwin32_signal_event != NULL);
+	if (WaitForSingleObject(pgwin32_signal_event,
+							(microsec < 500 ? 1 : (microsec + 500) / 1000))
+		== WAIT_OBJECT_0)
+	{
+		pgwin32_dispatch_queued_signals();
+		errno = EINTR;
+		return;
+	}
+}
+
+
+/* Initialization */
+void
+pgwin32_signal_initialize(void)
+{
+	int			i;
+	HANDLE		signal_thread_handle;
+
+	InitializeCriticalSection(&pg_signal_crit_sec);
+
+	for (i = 0; i < PG_SIGNAL_COUNT; i++)
+	{
+		pg_signal_array[i] = SIG_DFL;
+		pg_signal_defaults[i] = SIG_IGN;
+	}
+	pg_signal_mask = 0;
+	pg_signal_queue = 0;
+
+	/* Create the global event handle used to flag signals */
+	pgwin32_signal_event = CreateEvent(NULL, TRUE, FALSE, NULL);
+	if (pgwin32_signal_event == NULL)
+		ereport(FATAL,
+				(errmsg_internal("could not create signal event: error code %lu", GetLastError())));
+
+	/* Create thread for handling signals */
+	signal_thread_handle = CreateThread(NULL, 0, pg_signal_thread, NULL, 0, NULL);
+	if (signal_thread_handle == NULL)
+		ereport(FATAL,
+				(errmsg_internal("could not create signal handler thread")));
+
+	/* Create console control handle to pick up Ctrl-C etc */
+	if (!SetConsoleCtrlHandler(pg_console_handler, TRUE))
+		ereport(FATAL,
+				(errmsg_internal("could not set console control handler")));
+}
+
+/*
+ * Dispatch all signals currently queued and not blocked
+ * Blocked signals are ignored, and will be fired at the time of
+ * the pqsigsetmask() call.
+ */
+void
+pgwin32_dispatch_queued_signals(void)
+{
+	int			exec_mask;
+
+	Assert(pgwin32_signal_event != NULL);
+	EnterCriticalSection(&pg_signal_crit_sec);
+	while ((exec_mask = UNBLOCKED_SIGNAL_QUEUE()) != 0)
+	{
+		/* One or more unblocked signals queued for execution */
+		int			i;
+
+		for (i = 1; i < PG_SIGNAL_COUNT; i++)
+		{
+			if (exec_mask & sigmask(i))
+			{
+				/* Execute this signal */
+				pqsigfunc	sig = pg_signal_array[i];
+
+				if (sig == SIG_DFL)
+					sig = pg_signal_defaults[i];
+				pg_signal_queue &= ~sigmask(i);
+				if (sig != SIG_ERR && sig != SIG_IGN && sig != SIG_DFL)
+				{
+					LeaveCriticalSection(&pg_signal_crit_sec);
+					sig(i);
+					EnterCriticalSection(&pg_signal_crit_sec);
+					break;		/* Restart outer loop, in case signal mask or
+								 * queue has been modified inside signal
+								 * handler */
+				}
+			}
+		}
+	}
+	ResetEvent(pgwin32_signal_event);
+	LeaveCriticalSection(&pg_signal_crit_sec);
+}
+
+/* signal masking. Only called on main thread, no sync required */
+int
+pqsigsetmask(int mask)
+{
+	int			prevmask;
+
+	prevmask = pg_signal_mask;
+	pg_signal_mask = mask;
+
+	/*
+	 * Dispatch any signals queued up right away, in case we have unblocked
+	 * one or more signals previously queued
+	 */
+	pgwin32_dispatch_queued_signals();
+
+	return prevmask;
+}
+
+
+/*
+ * Unix-like signal handler installation
+ *
+ * Only called on main thread, no sync required
+ */
+pqsigfunc
+pqsignal(int signum, pqsigfunc handler)
+{
+	pqsigfunc	prevfunc;
+
+	if (signum >= PG_SIGNAL_COUNT || signum < 0)
+		return SIG_ERR;
+	prevfunc = pg_signal_array[signum];
+	pg_signal_array[signum] = handler;
+	return prevfunc;
+}
+
+/* Create the signal listener pipe for specified PID */
+HANDLE
+pgwin32_create_signal_listener(pid_t pid)
+{
+	char		pipename[128];
+	HANDLE		pipe;
+
+	snprintf(pipename, sizeof(pipename), "\\\\.\\pipe\\pgsignal_%u", (int) pid);
+
+	pipe = CreateNamedPipe(pipename, PIPE_ACCESS_DUPLEX,
+						   PIPE_TYPE_MESSAGE | PIPE_READMODE_MESSAGE | PIPE_WAIT,
+						   PIPE_UNLIMITED_INSTANCES, 16, 16, 1000, NULL);
+
+	if (pipe == INVALID_HANDLE_VALUE)
+		ereport(ERROR,
+				(errmsg("could not create signal listener pipe for PID %d: error code %lu",
+						(int) pid, GetLastError())));
+
+	return pipe;
+}
+
+
+/*
+ * All functions below execute on the signal handler thread
+ * and must be synchronized as such!
+ * NOTE! The only global variable that can be used is
+ * pg_signal_queue!
+ */
+
+
+/*
+ * Queue a signal for the main thread, by setting the flag bit and event.
+ */
+void
+pg_queue_signal(int signum)
+{
+	Assert(pgwin32_signal_event != NULL);
+	if (signum >= PG_SIGNAL_COUNT || signum <= 0)
+		return;					/* ignore any bad signal number */
+
+	EnterCriticalSection(&pg_signal_crit_sec);
+	pg_signal_queue |= sigmask(signum);
+	LeaveCriticalSection(&pg_signal_crit_sec);
+
+	SetEvent(pgwin32_signal_event);
+}
+
+/* Signal handling thread */
+static DWORD WINAPI
+pg_signal_thread(LPVOID param)
+{
+	char		pipename[128];
+	HANDLE		pipe = pgwin32_initial_signal_pipe;
+
+	/* Set up pipe name, in case we have to re-create the pipe. */
+	snprintf(pipename, sizeof(pipename), "\\\\.\\pipe\\pgsignal_%lu", GetCurrentProcessId());
+
+	for (;;)
+	{
+		BOOL		fConnected;
+
+		/* Create a new pipe instance if we don't have one. */
+		if (pipe == INVALID_HANDLE_VALUE)
+		{
+			pipe = CreateNamedPipe(pipename, PIPE_ACCESS_DUPLEX,
+								   PIPE_TYPE_MESSAGE | PIPE_READMODE_MESSAGE | PIPE_WAIT,
+								   PIPE_UNLIMITED_INSTANCES, 16, 16, 1000, NULL);
+
+			if (pipe == INVALID_HANDLE_VALUE)
+			{
+				write_stderr("could not create signal listener pipe: error code %lu; retrying\n", GetLastError());
+				SleepEx(500, FALSE);
+				continue;
+			}
+		}
+
+		/*
+		 * Wait for a client to connect.  If something connects before we
+		 * reach here, we'll get back a "failure" with ERROR_PIPE_CONNECTED,
+		 * which is actually a success (way to go, Microsoft).
+		 */
+		fConnected = ConnectNamedPipe(pipe, NULL) ? TRUE : (GetLastError() == ERROR_PIPE_CONNECTED);
+		if (fConnected)
+		{
+			/*
+			 * We have a connection from a would-be signal sender. Process it.
+			 */
+			BYTE		sigNum;
+			DWORD		bytes;
+
+			if (ReadFile(pipe, &sigNum, 1, &bytes, NULL) &&
+				bytes == 1)
+			{
+				/*
+				 * Queue the signal before responding to the client.  In this
+				 * way, it's guaranteed that once kill() has returned in the
+				 * signal sender, the next CHECK_FOR_INTERRUPTS() in the
+				 * signal recipient will see the signal.  (This is a stronger
+				 * guarantee than POSIX makes; maybe we don't need it?  But
+				 * without it, we've seen timing bugs on Windows that do not
+				 * manifest on any known Unix.)
+				 */
+				pg_queue_signal(sigNum);
+
+				/*
+				 * Write something back to the client, allowing its
+				 * CallNamedPipe() call to terminate.
+				 */
+				WriteFile(pipe, &sigNum, 1, &bytes, NULL);	/* Don't care if it
+															 * works or not */
+
+				/*
+				 * We must wait for the client to read the data before we can
+				 * disconnect, else the data will be lost.  (If the WriteFile
+				 * call failed, there'll be nothing in the buffer, so this
+				 * shouldn't block.)
+				 */
+				FlushFileBuffers(pipe);
+			}
+			else
+			{
+				/*
+				 * If we fail to read a byte from the client, assume it's the
+				 * client's problem and do nothing.  Perhaps it'd be better to
+				 * force a pipe close and reopen?
+				 */
+			}
+
+			/* Disconnect from client so that we can re-use the pipe. */
+			DisconnectNamedPipe(pipe);
+		}
+		else
+		{
+			/*
+			 * Connection failed.  Cleanup and try again.
+			 *
+			 * This should never happen.  If it does, there's a window where
+			 * we'll miss signals until we manage to re-create the pipe.
+			 * However, just trying to use the same pipe again is probably not
+			 * going to work, so we have little choice.
+			 */
+			CloseHandle(pipe);
+			pipe = INVALID_HANDLE_VALUE;
+		}
+	}
+	return 0;
+}
+
+
+/* Console control handler will execute on a thread created
+   by the OS at the time of invocation */
+static BOOL WINAPI
+pg_console_handler(DWORD dwCtrlType)
+{
+	if (dwCtrlType == CTRL_C_EVENT ||
+		dwCtrlType == CTRL_BREAK_EVENT ||
+		dwCtrlType == CTRL_CLOSE_EVENT ||
+		dwCtrlType == CTRL_SHUTDOWN_EVENT)
+	{
+		pg_queue_signal(SIGINT);
+		return TRUE;
+	}
+	return FALSE;
+}
diff --git a/src/backend/port/win32/socket.c b/src/backend/port/win32/socket.c
new file mode 100644
index 0000000..6fbd1ed
--- /dev/null
+++ b/src/backend/port/win32/socket.c
@@ -0,0 +1,692 @@
+/*-------------------------------------------------------------------------
+ *
+ * socket.c
+ *	  Microsoft Windows Win32 Socket Functions
+ *
+ * Portions Copyright (c) 1996-2020, PostgreSQL Global Development Group
+ *
+ * IDENTIFICATION
+ *	  src/backend/port/win32/socket.c
+ *
+ *-------------------------------------------------------------------------
+ */
+
+#include "postgres.h"
+
+/*
+ * Indicate if pgwin32_recv() and pgwin32_send() should operate
+ * in non-blocking mode.
+ *
+ * Since the socket emulation layer always sets the actual socket to
+ * non-blocking mode in order to be able to deliver signals, we must
+ * specify this in a separate flag if we actually need non-blocking
+ * operation.
+ *
+ * This flag changes the behaviour *globally* for all socket operations,
+ * so it should only be set for very short periods of time.
+ */
+int			pgwin32_noblock = 0;
+
+/* Undef the macros defined in win32.h, so we can access system functions */
+#undef socket
+#undef bind
+#undef listen
+#undef accept
+#undef connect
+#undef select
+#undef recv
+#undef send
+
+/*
+ * Blocking socket functions implemented so they listen on both
+ * the socket and the signal event, required for signal handling.
+ */
+
+/*
+ * Convert the last socket error code into errno
+ *
+ * Note: where there is a direct correspondence between a WSAxxx error code
+ * and a Berkeley error symbol, this mapping is actually a no-op, because
+ * in win32.h we redefine the network-related Berkeley error symbols to have
+ * the values of their WSAxxx counterparts.  The point of the switch is
+ * mostly to translate near-miss error codes into something that's sensible
+ * in the Berkeley universe.
+ */
+static void
+TranslateSocketError(void)
+{
+	switch (WSAGetLastError())
+	{
+		case WSAEINVAL:
+		case WSANOTINITIALISED:
+		case WSAEINVALIDPROVIDER:
+		case WSAEINVALIDPROCTABLE:
+		case WSAEDESTADDRREQ:
+			errno = EINVAL;
+			break;
+		case WSAEINPROGRESS:
+			errno = EINPROGRESS;
+			break;
+		case WSAEFAULT:
+			errno = EFAULT;
+			break;
+		case WSAEISCONN:
+			errno = EISCONN;
+			break;
+		case WSAEMSGSIZE:
+			errno = EMSGSIZE;
+			break;
+		case WSAEAFNOSUPPORT:
+			errno = EAFNOSUPPORT;
+			break;
+		case WSAEMFILE:
+			errno = EMFILE;
+			break;
+		case WSAENOBUFS:
+			errno = ENOBUFS;
+			break;
+		case WSAEPROTONOSUPPORT:
+		case WSAEPROTOTYPE:
+		case WSAESOCKTNOSUPPORT:
+			errno = EPROTONOSUPPORT;
+			break;
+		case WSAECONNABORTED:
+			errno = ECONNABORTED;
+			break;
+		case WSAECONNREFUSED:
+			errno = ECONNREFUSED;
+			break;
+		case WSAECONNRESET:
+			errno = ECONNRESET;
+			break;
+		case WSAEINTR:
+			errno = EINTR;
+			break;
+		case WSAENOTSOCK:
+			errno = ENOTSOCK;
+			break;
+		case WSAEOPNOTSUPP:
+			errno = EOPNOTSUPP;
+			break;
+		case WSAEWOULDBLOCK:
+			errno = EWOULDBLOCK;
+			break;
+		case WSAEACCES:
+			errno = EACCES;
+			break;
+		case WSAEADDRINUSE:
+			errno = EADDRINUSE;
+			break;
+		case WSAEADDRNOTAVAIL:
+			errno = EADDRNOTAVAIL;
+			break;
+		case WSAEHOSTUNREACH:
+		case WSAEHOSTDOWN:
+		case WSAHOST_NOT_FOUND:
+		case WSAENETDOWN:
+		case WSAENETUNREACH:
+		case WSAENETRESET:
+			errno = EHOSTUNREACH;
+			break;
+		case WSAENOTCONN:
+		case WSAESHUTDOWN:
+		case WSAEDISCON:
+			errno = ENOTCONN;
+			break;
+		default:
+			ereport(NOTICE,
+					(errmsg_internal("unrecognized win32 socket error code: %d", WSAGetLastError())));
+			errno = EINVAL;
+	}
+}
+
+static int
+pgwin32_poll_signals(void)
+{
+	if (UNBLOCKED_SIGNAL_QUEUE())
+	{
+		pgwin32_dispatch_queued_signals();
+		errno = EINTR;
+		return 1;
+	}
+	return 0;
+}
+
+static int
+isDataGram(SOCKET s)
+{
+	int			type;
+	int			typelen = sizeof(type);
+
+	if (getsockopt(s, SOL_SOCKET, SO_TYPE, (char *) &type, &typelen))
+		return 1;
+
+	return (type == SOCK_DGRAM) ? 1 : 0;
+}
+
+int
+pgwin32_waitforsinglesocket(SOCKET s, int what, int timeout)
+{
+	static HANDLE waitevent = INVALID_HANDLE_VALUE;
+	static SOCKET current_socket = INVALID_SOCKET;
+	static int	isUDP = 0;
+	HANDLE		events[2];
+	int			r;
+
+	/* Create an event object just once and use it on all future calls */
+	if (waitevent == INVALID_HANDLE_VALUE)
+	{
+		waitevent = CreateEvent(NULL, TRUE, FALSE, NULL);
+
+		if (waitevent == INVALID_HANDLE_VALUE)
+			ereport(ERROR,
+					(errmsg_internal("could not create socket waiting event: error code %lu", GetLastError())));
+	}
+	else if (!ResetEvent(waitevent))
+		ereport(ERROR,
+				(errmsg_internal("could not reset socket waiting event: error code %lu", GetLastError())));
+
+	/*
+	 * Track whether socket is UDP or not.  (NB: most likely, this is both
+	 * useless and wrong; there is no reason to think that the behavior of
+	 * WSAEventSelect is different for TCP and UDP.)
+	 */
+	if (current_socket != s)
+		isUDP = isDataGram(s);
+	current_socket = s;
+
+	/*
+	 * Attach event to socket.  NOTE: we must detach it again before
+	 * returning, since other bits of code may try to attach other events to
+	 * the socket.
+	 */
+	if (WSAEventSelect(s, waitevent, what) != 0)
+	{
+		TranslateSocketError();
+		return 0;
+	}
+
+	events[0] = pgwin32_signal_event;
+	events[1] = waitevent;
+
+	/*
+	 * Just a workaround of unknown locking problem with writing in UDP socket
+	 * under high load: Client's pgsql backend sleeps infinitely in
+	 * WaitForMultipleObjectsEx, pgstat process sleeps in pgwin32_select().
+	 * So, we will wait with small timeout(0.1 sec) and if socket is still
+	 * blocked, try WSASend (see comments in pgwin32_select) and wait again.
+	 */
+	if ((what & FD_WRITE) && isUDP)
+	{
+		for (;;)
+		{
+			r = WaitForMultipleObjectsEx(2, events, FALSE, 100, TRUE);
+
+			if (r == WAIT_TIMEOUT)
+			{
+				char		c;
+				WSABUF		buf;
+				DWORD		sent;
+
+				buf.buf = &c;
+				buf.len = 0;
+
+				r = WSASend(s, &buf, 1, &sent, 0, NULL, NULL);
+				if (r == 0)		/* Completed - means things are fine! */
+				{
+					WSAEventSelect(s, NULL, 0);
+					return 1;
+				}
+				else if (WSAGetLastError() != WSAEWOULDBLOCK)
+				{
+					TranslateSocketError();
+					WSAEventSelect(s, NULL, 0);
+					return 0;
+				}
+			}
+			else
+				break;
+		}
+	}
+	else
+		r = WaitForMultipleObjectsEx(2, events, FALSE, timeout, TRUE);
+
+	WSAEventSelect(s, NULL, 0);
+
+	if (r == WAIT_OBJECT_0 || r == WAIT_IO_COMPLETION)
+	{
+		pgwin32_dispatch_queued_signals();
+		errno = EINTR;
+		return 0;
+	}
+	if (r == WAIT_OBJECT_0 + 1)
+		return 1;
+	if (r == WAIT_TIMEOUT)
+	{
+		errno = EWOULDBLOCK;
+		return 0;
+	}
+	ereport(ERROR,
+			(errmsg_internal("unrecognized return value from WaitForMultipleObjects: %d (error code %lu)", r, GetLastError())));
+	return 0;
+}
+
+/*
+ * Create a socket, setting it to overlapped and non-blocking
+ */
+SOCKET
+pgwin32_socket(int af, int type, int protocol)
+{
+	SOCKET		s;
+	unsigned long on = 1;
+
+	s = WSASocket(af, type, protocol, NULL, 0, WSA_FLAG_OVERLAPPED);
+	if (s == INVALID_SOCKET)
+	{
+		TranslateSocketError();
+		return INVALID_SOCKET;
+	}
+
+	if (ioctlsocket(s, FIONBIO, &on))
+	{
+		TranslateSocketError();
+		return INVALID_SOCKET;
+	}
+	errno = 0;
+
+	return s;
+}
+
+int
+pgwin32_bind(SOCKET s, struct sockaddr *addr, int addrlen)
+{
+	int			res;
+
+	res = bind(s, addr, addrlen);
+	if (res < 0)
+		TranslateSocketError();
+	return res;
+}
+
+int
+pgwin32_listen(SOCKET s, int backlog)
+{
+	int			res;
+
+	res = listen(s, backlog);
+	if (res < 0)
+		TranslateSocketError();
+	return res;
+}
+
+SOCKET
+pgwin32_accept(SOCKET s, struct sockaddr *addr, int *addrlen)
+{
+	SOCKET		rs;
+
+	/*
+	 * Poll for signals, but don't return with EINTR, since we don't handle
+	 * that in pqcomm.c
+	 */
+	pgwin32_poll_signals();
+
+	rs = WSAAccept(s, addr, addrlen, NULL, 0);
+	if (rs == INVALID_SOCKET)
+	{
+		TranslateSocketError();
+		return INVALID_SOCKET;
+	}
+	return rs;
+}
+
+
+/* No signal delivery during connect. */
+int
+pgwin32_connect(SOCKET s, const struct sockaddr *addr, int addrlen)
+{
+	int			r;
+
+	r = WSAConnect(s, addr, addrlen, NULL, NULL, NULL, NULL);
+	if (r == 0)
+		return 0;
+
+	if (WSAGetLastError() != WSAEWOULDBLOCK)
+	{
+		TranslateSocketError();
+		return -1;
+	}
+
+	while (pgwin32_waitforsinglesocket(s, FD_CONNECT, INFINITE) == 0)
+	{
+		/* Loop endlessly as long as we are just delivering signals */
+	}
+
+	return 0;
+}
+
+int
+pgwin32_recv(SOCKET s, char *buf, int len, int f)
+{
+	WSABUF		wbuf;
+	int			r;
+	DWORD		b;
+	DWORD		flags = f;
+	int			n;
+
+	if (pgwin32_poll_signals())
+		return -1;
+
+	wbuf.len = len;
+	wbuf.buf = buf;
+
+	r = WSARecv(s, &wbuf, 1, &b, &flags, NULL, NULL);
+	if (r != SOCKET_ERROR)
+		return b;				/* success */
+
+	if (WSAGetLastError() != WSAEWOULDBLOCK)
+	{
+		TranslateSocketError();
+		return -1;
+	}
+
+	if (pgwin32_noblock)
+	{
+		/*
+		 * No data received, and we are in "emulated non-blocking mode", so
+		 * return indicating that we'd block if we were to continue.
+		 */
+		errno = EWOULDBLOCK;
+		return -1;
+	}
+
+	/* We're in blocking mode, so wait for data */
+
+	for (n = 0; n < 5; n++)
+	{
+		if (pgwin32_waitforsinglesocket(s, FD_READ | FD_CLOSE | FD_ACCEPT,
+										INFINITE) == 0)
+			return -1;			/* errno already set */
+
+		r = WSARecv(s, &wbuf, 1, &b, &flags, NULL, NULL);
+		if (r != SOCKET_ERROR)
+			return b;			/* success */
+		if (WSAGetLastError() != WSAEWOULDBLOCK)
+		{
+			TranslateSocketError();
+			return -1;
+		}
+
+		/*
+		 * There seem to be cases on win2k (at least) where WSARecv can return
+		 * WSAEWOULDBLOCK even when pgwin32_waitforsinglesocket claims the
+		 * socket is readable.  In this case, just sleep for a moment and try
+		 * again.  We try up to 5 times - if it fails more than that it's not
+		 * likely to ever come back.
+		 */
+		pg_usleep(10000);
+	}
+	ereport(NOTICE,
+			(errmsg_internal("could not read from ready socket (after retries)")));
+	errno = EWOULDBLOCK;
+	return -1;
+}
+
+/*
+ * The second argument to send() is defined by SUS to be a "const void *"
+ * and so we use the same signature here to keep compilers happy when
+ * handling callers.
+ *
+ * But the buf member of a WSABUF struct is defined as "char *", so we cast
+ * the second argument to that here when assigning it, also to keep compilers
+ * happy.
+ */
+
+int
+pgwin32_send(SOCKET s, const void *buf, int len, int flags)
+{
+	WSABUF		wbuf;
+	int			r;
+	DWORD		b;
+
+	if (pgwin32_poll_signals())
+		return -1;
+
+	wbuf.len = len;
+	wbuf.buf = (char *) buf;
+
+	/*
+	 * Readiness of socket to send data to UDP socket may be not true: socket
+	 * can become busy again! So loop until send or error occurs.
+	 */
+	for (;;)
+	{
+		r = WSASend(s, &wbuf, 1, &b, flags, NULL, NULL);
+		if (r != SOCKET_ERROR && b > 0)
+			/* Write succeeded right away */
+			return b;
+
+		if (r == SOCKET_ERROR &&
+			WSAGetLastError() != WSAEWOULDBLOCK)
+		{
+			TranslateSocketError();
+			return -1;
+		}
+
+		if (pgwin32_noblock)
+		{
+			/*
+			 * No data sent, and we are in "emulated non-blocking mode", so
+			 * return indicating that we'd block if we were to continue.
+			 */
+			errno = EWOULDBLOCK;
+			return -1;
+		}
+
+		/* No error, zero bytes (win2000+) or error+WSAEWOULDBLOCK (<=nt4) */
+
+		if (pgwin32_waitforsinglesocket(s, FD_WRITE | FD_CLOSE, INFINITE) == 0)
+			return -1;
+	}
+
+	return -1;
+}
+
+
+/*
+ * Wait for activity on one or more sockets.
+ * While waiting, allow signals to run
+ *
+ * NOTE! Currently does not implement exceptfds check,
+ * since it is not used in postgresql!
+ */
+int
+pgwin32_select(int nfds, fd_set *readfds, fd_set *writefds, fd_set *exceptfds, const struct timeval *timeout)
+{
+	WSAEVENT	events[FD_SETSIZE * 2]; /* worst case is readfds totally
+										 * different from writefds, so
+										 * 2*FD_SETSIZE sockets */
+	SOCKET		sockets[FD_SETSIZE * 2];
+	int			numevents = 0;
+	int			i;
+	int			r;
+	DWORD		timeoutval = WSA_INFINITE;
+	FD_SET		outreadfds;
+	FD_SET		outwritefds;
+	int			nummatches = 0;
+
+	Assert(exceptfds == NULL);
+
+	if (pgwin32_poll_signals())
+		return -1;
+
+	FD_ZERO(&outreadfds);
+	FD_ZERO(&outwritefds);
+
+	/*
+	 * Windows does not guarantee to log an FD_WRITE network event indicating
+	 * that more data can be sent unless the previous send() failed with
+	 * WSAEWOULDBLOCK.  While our caller might well have made such a call, we
+	 * cannot assume that here.  Therefore, if waiting for write-ready, force
+	 * the issue by doing a dummy send().  If the dummy send() succeeds,
+	 * assume that the socket is in fact write-ready, and return immediately.
+	 * Also, if it fails with something other than WSAEWOULDBLOCK, return a
+	 * write-ready indication to let our caller deal with the error condition.
+	 */
+	if (writefds != NULL)
+	{
+		for (i = 0; i < writefds->fd_count; i++)
+		{
+			char		c;
+			WSABUF		buf;
+			DWORD		sent;
+
+			buf.buf = &c;
+			buf.len = 0;
+
+			r = WSASend(writefds->fd_array[i], &buf, 1, &sent, 0, NULL, NULL);
+			if (r == 0 || WSAGetLastError() != WSAEWOULDBLOCK)
+				FD_SET(writefds->fd_array[i], &outwritefds);
+		}
+
+		/* If we found any write-ready sockets, just return them immediately */
+		if (outwritefds.fd_count > 0)
+		{
+			memcpy(writefds, &outwritefds, sizeof(fd_set));
+			if (readfds)
+				FD_ZERO(readfds);
+			return outwritefds.fd_count;
+		}
+	}
+
+
+	/* Now set up for an actual select */
+
+	if (timeout != NULL)
+	{
+		/* timeoutval is in milliseconds */
+		timeoutval = timeout->tv_sec * 1000 + timeout->tv_usec / 1000;
+	}
+
+	if (readfds != NULL)
+	{
+		for (i = 0; i < readfds->fd_count; i++)
+		{
+			events[numevents] = WSACreateEvent();
+			sockets[numevents] = readfds->fd_array[i];
+			numevents++;
+		}
+	}
+	if (writefds != NULL)
+	{
+		for (i = 0; i < writefds->fd_count; i++)
+		{
+			if (!readfds ||
+				!FD_ISSET(writefds->fd_array[i], readfds))
+			{
+				/* If the socket is not in the read list */
+				events[numevents] = WSACreateEvent();
+				sockets[numevents] = writefds->fd_array[i];
+				numevents++;
+			}
+		}
+	}
+
+	for (i = 0; i < numevents; i++)
+	{
+		int			flags = 0;
+
+		if (readfds && FD_ISSET(sockets[i], readfds))
+			flags |= FD_READ | FD_ACCEPT | FD_CLOSE;
+
+		if (writefds && FD_ISSET(sockets[i], writefds))
+			flags |= FD_WRITE | FD_CLOSE;
+
+		if (WSAEventSelect(sockets[i], events[i], flags) != 0)
+		{
+			TranslateSocketError();
+			/* release already-assigned event objects */
+			while (--i >= 0)
+				WSAEventSelect(sockets[i], NULL, 0);
+			for (i = 0; i < numevents; i++)
+				WSACloseEvent(events[i]);
+			return -1;
+		}
+	}
+
+	events[numevents] = pgwin32_signal_event;
+	r = WaitForMultipleObjectsEx(numevents + 1, events, FALSE, timeoutval, TRUE);
+	if (r != WAIT_TIMEOUT && r != WAIT_IO_COMPLETION && r != (WAIT_OBJECT_0 + numevents))
+	{
+		/*
+		 * We scan all events, even those not signaled, in case more than one
+		 * event has been tagged but Wait.. can only return one.
+		 */
+		WSANETWORKEVENTS resEvents;
+
+		for (i = 0; i < numevents; i++)
+		{
+			ZeroMemory(&resEvents, sizeof(resEvents));
+			if (WSAEnumNetworkEvents(sockets[i], events[i], &resEvents) != 0)
+				elog(ERROR, "failed to enumerate network events: error code %u",
+					 WSAGetLastError());
+			/* Read activity? */
+			if (readfds && FD_ISSET(sockets[i], readfds))
+			{
+				if ((resEvents.lNetworkEvents & FD_READ) ||
+					(resEvents.lNetworkEvents & FD_ACCEPT) ||
+					(resEvents.lNetworkEvents & FD_CLOSE))
+				{
+					FD_SET(sockets[i], &outreadfds);
+
+					nummatches++;
+				}
+			}
+			/* Write activity? */
+			if (writefds && FD_ISSET(sockets[i], writefds))
+			{
+				if ((resEvents.lNetworkEvents & FD_WRITE) ||
+					(resEvents.lNetworkEvents & FD_CLOSE))
+				{
+					FD_SET(sockets[i], &outwritefds);
+
+					nummatches++;
+				}
+			}
+		}
+	}
+
+	/* Clean up all the event objects */
+	for (i = 0; i < numevents; i++)
+	{
+		WSAEventSelect(sockets[i], NULL, 0);
+		WSACloseEvent(events[i]);
+	}
+
+	if (r == WSA_WAIT_TIMEOUT)
+	{
+		if (readfds)
+			FD_ZERO(readfds);
+		if (writefds)
+			FD_ZERO(writefds);
+		return 0;
+	}
+
+	/* Signal-like events. */
+	if (r == WAIT_OBJECT_0 + numevents || r == WAIT_IO_COMPLETION)
+	{
+		pgwin32_dispatch_queued_signals();
+		errno = EINTR;
+		if (readfds)
+			FD_ZERO(readfds);
+		if (writefds)
+			FD_ZERO(writefds);
+		return -1;
+	}
+
+	/* Overwrite socket sets with our resulting values */
+	if (readfds)
+		memcpy(readfds, &outreadfds, sizeof(fd_set));
+	if (writefds)
+		memcpy(writefds, &outwritefds, sizeof(fd_set));
+	return nummatches;
+}
diff --git a/src/backend/port/win32/timer.c b/src/backend/port/win32/timer.c
new file mode 100644
index 0000000..bb98178
--- /dev/null
+++ b/src/backend/port/win32/timer.c
@@ -0,0 +1,121 @@
+/*-------------------------------------------------------------------------
+ *
+ * timer.c
+ *	  Microsoft Windows Win32 Timer Implementation
+ *
+ *	  Limitations of this implementation:
+ *
+ *	  - Does not support interval timer (value->it_interval)
+ *	  - Only supports ITIMER_REAL
+ *
+ * Portions Copyright (c) 1996-2020, PostgreSQL Global Development Group
+ *
+ * IDENTIFICATION
+ *	  src/backend/port/win32/timer.c
+ *
+ *-------------------------------------------------------------------------
+ */
+
+#include "postgres.h"
+
+
+/* Communication area for inter-thread communication */
+typedef struct timerCA
+{
+	struct itimerval value;
+	HANDLE		event;
+	CRITICAL_SECTION crit_sec;
+} timerCA;
+
+static timerCA timerCommArea;
+static HANDLE timerThreadHandle = INVALID_HANDLE_VALUE;
+
+
+/* Timer management thread */
+static DWORD WINAPI
+pg_timer_thread(LPVOID param)
+{
+	DWORD		waittime;
+
+	Assert(param == NULL);
+
+	waittime = INFINITE;
+
+	for (;;)
+	{
+		int			r;
+
+		r = WaitForSingleObjectEx(timerCommArea.event, waittime, FALSE);
+		if (r == WAIT_OBJECT_0)
+		{
+			/* Event signaled from main thread, change the timer */
+			EnterCriticalSection(&timerCommArea.crit_sec);
+			if (timerCommArea.value.it_value.tv_sec == 0 &&
+				timerCommArea.value.it_value.tv_usec == 0)
+				waittime = INFINITE;	/* Cancel the interrupt */
+			else
+			{
+				/* WaitForSingleObjectEx() uses milliseconds, round up */
+				waittime = (timerCommArea.value.it_value.tv_usec + 999) / 1000 +
+					timerCommArea.value.it_value.tv_sec * 1000;
+			}
+			ResetEvent(timerCommArea.event);
+			LeaveCriticalSection(&timerCommArea.crit_sec);
+		}
+		else if (r == WAIT_TIMEOUT)
+		{
+			/* Timeout expired, signal SIGALRM and turn it off */
+			pg_queue_signal(SIGALRM);
+			waittime = INFINITE;
+		}
+		else
+		{
+			/* Should never happen */
+			Assert(false);
+		}
+	}
+
+	return 0;
+}
+
+/*
+ * Win32 setitimer emulation by creating a persistent thread
+ * to handle the timer setting and notification upon timeout.
+ */
+int
+setitimer(int which, const struct itimerval *value, struct itimerval *ovalue)
+{
+	Assert(value != NULL);
+	Assert(value->it_interval.tv_sec == 0 && value->it_interval.tv_usec == 0);
+	Assert(which == ITIMER_REAL);
+
+	if (timerThreadHandle == INVALID_HANDLE_VALUE)
+	{
+		/* First call in this backend, create event and the timer thread */
+		timerCommArea.event = CreateEvent(NULL, TRUE, FALSE, NULL);
+		if (timerCommArea.event == NULL)
+			ereport(FATAL,
+					(errmsg_internal("could not create timer event: error code %lu",
+									 GetLastError())));
+
+		MemSet(&timerCommArea.value, 0, sizeof(struct itimerval));
+
+		InitializeCriticalSection(&timerCommArea.crit_sec);
+
+		timerThreadHandle = CreateThread(NULL, 0, pg_timer_thread, NULL, 0, NULL);
+		if (timerThreadHandle == INVALID_HANDLE_VALUE)
+			ereport(FATAL,
+					(errmsg_internal("could not create timer thread: error code %lu",
+									 GetLastError())));
+	}
+
+	/* Request the timer thread to change settings */
+	EnterCriticalSection(&timerCommArea.crit_sec);
+	if (ovalue)
+		*ovalue = timerCommArea.value;
+	timerCommArea.value = *value;
+	LeaveCriticalSection(&timerCommArea.crit_sec);
+	SetEvent(timerCommArea.event);
+
+	return 0;
+}
diff --git a/src/backend/port/win32_sema.c b/src/backend/port/win32_sema.c
new file mode 100644
index 0000000..d15c4c1
--- /dev/null
+++ b/src/backend/port/win32_sema.c
@@ -0,0 +1,235 @@
+/*-------------------------------------------------------------------------
+ *
+ * win32_sema.c
+ *	  Microsoft Windows Win32 Semaphores Emulation
+ *
+ * Portions Copyright (c) 1996-2020, PostgreSQL Global Development Group
+ *
+ * IDENTIFICATION
+ *	  src/backend/port/win32_sema.c
+ *
+ *-------------------------------------------------------------------------
+ */
+
+#include "postgres.h"
+
+#include "miscadmin.h"
+#include "storage/ipc.h"
+#include "storage/pg_sema.h"
+
+static HANDLE *mySemSet;		/* IDs of sema sets acquired so far */
+static int	numSems;			/* number of sema sets acquired so far */
+static int	maxSems;			/* allocated size of mySemaSet array */
+
+static void ReleaseSemaphores(int code, Datum arg);
+
+
+/*
+ * Report amount of shared memory needed for semaphores
+ */
+Size
+PGSemaphoreShmemSize(int maxSemas)
+{
+	/* No shared memory needed on Windows */
+	return 0;
+}
+
+/*
+ * PGReserveSemaphores --- initialize semaphore support
+ *
+ * In the Win32 implementation, we acquire semaphores on-demand; the
+ * maxSemas parameter is just used to size the array that keeps track of
+ * acquired semas for subsequent releasing.  We use anonymous semaphores
+ * so the semaphores are automatically freed when the last referencing
+ * process exits.
+ */
+void
+PGReserveSemaphores(int maxSemas)
+{
+	mySemSet = (HANDLE *) malloc(maxSemas * sizeof(HANDLE));
+	if (mySemSet == NULL)
+		elog(PANIC, "out of memory");
+	numSems = 0;
+	maxSems = maxSemas;
+
+	on_shmem_exit(ReleaseSemaphores, 0);
+}
+
+/*
+ * Release semaphores at shutdown or shmem reinitialization
+ *
+ * (called as an on_shmem_exit callback, hence funny argument list)
+ */
+static void
+ReleaseSemaphores(int code, Datum arg)
+{
+	int			i;
+
+	for (i = 0; i < numSems; i++)
+		CloseHandle(mySemSet[i]);
+	free(mySemSet);
+}
+
+/*
+ * PGSemaphoreCreate
+ *
+ * Allocate a PGSemaphore structure with initial count 1
+ */
+PGSemaphore
+PGSemaphoreCreate(void)
+{
+	HANDLE		cur_handle;
+	SECURITY_ATTRIBUTES sec_attrs;
+
+	/* Can't do this in a backend, because static state is postmaster's */
+	Assert(!IsUnderPostmaster);
+
+	if (numSems >= maxSems)
+		elog(PANIC, "too many semaphores created");
+
+	ZeroMemory(&sec_attrs, sizeof(sec_attrs));
+	sec_attrs.nLength = sizeof(sec_attrs);
+	sec_attrs.lpSecurityDescriptor = NULL;
+	sec_attrs.bInheritHandle = TRUE;
+
+	/* We don't need a named semaphore */
+	cur_handle = CreateSemaphore(&sec_attrs, 1, 32767, NULL);
+	if (cur_handle)
+	{
+		/* Successfully done */
+		mySemSet[numSems++] = cur_handle;
+	}
+	else
+		ereport(PANIC,
+				(errmsg("could not create semaphore: error code %lu",
+						GetLastError())));
+
+	return (PGSemaphore) cur_handle;
+}
+
+/*
+ * PGSemaphoreReset
+ *
+ * Reset a previously-initialized PGSemaphore to have count 0
+ */
+void
+PGSemaphoreReset(PGSemaphore sema)
+{
+	/*
+	 * There's no direct API for this in Win32, so we have to ratchet the
+	 * semaphore down to 0 with repeated trylock's.
+	 */
+	while (PGSemaphoreTryLock(sema))
+		 /* loop */ ;
+}
+
+/*
+ * PGSemaphoreLock
+ *
+ * Lock a semaphore (decrement count), blocking if count would be < 0.
+ */
+void
+PGSemaphoreLock(PGSemaphore sema)
+{
+	HANDLE		wh[2];
+	bool		done = false;
+
+	/*
+	 * Note: pgwin32_signal_event should be first to ensure that it will be
+	 * reported when multiple events are set.  We want to guarantee that
+	 * pending signals are serviced.
+	 */
+	wh[0] = pgwin32_signal_event;
+	wh[1] = sema;
+
+	/*
+	 * As in other implementations of PGSemaphoreLock, we need to check for
+	 * cancel/die interrupts each time through the loop.  But here, there is
+	 * no hidden magic about whether the syscall will internally service a
+	 * signal --- we do that ourselves.
+	 */
+	while (!done)
+	{
+		DWORD		rc;
+
+		CHECK_FOR_INTERRUPTS();
+
+		rc = WaitForMultipleObjectsEx(2, wh, FALSE, INFINITE, TRUE);
+		switch (rc)
+		{
+			case WAIT_OBJECT_0:
+				/* Signal event is set - we have a signal to deliver */
+				pgwin32_dispatch_queued_signals();
+				break;
+			case WAIT_OBJECT_0 + 1:
+				/* We got it! */
+				done = true;
+				break;
+			case WAIT_IO_COMPLETION:
+
+				/*
+				 * The system interrupted the wait to execute an I/O
+				 * completion routine or asynchronous procedure call in this
+				 * thread.  PostgreSQL does not provoke either of these, but
+				 * atypical loaded DLLs or even other processes might do so.
+				 * Now, resume waiting.
+				 */
+				break;
+			case WAIT_FAILED:
+				ereport(FATAL,
+						(errmsg("could not lock semaphore: error code %lu",
+								GetLastError())));
+				break;
+			default:
+				elog(FATAL, "unexpected return code from WaitForMultipleObjectsEx(): %lu", rc);
+				break;
+		}
+	}
+}
+
+/*
+ * PGSemaphoreUnlock
+ *
+ * Unlock a semaphore (increment count)
+ */
+void
+PGSemaphoreUnlock(PGSemaphore sema)
+{
+	if (!ReleaseSemaphore(sema, 1, NULL))
+		ereport(FATAL,
+				(errmsg("could not unlock semaphore: error code %lu",
+						GetLastError())));
+}
+
+/*
+ * PGSemaphoreTryLock
+ *
+ * Lock a semaphore only if able to do so without blocking
+ */
+bool
+PGSemaphoreTryLock(PGSemaphore sema)
+{
+	DWORD		ret;
+
+	ret = WaitForSingleObject(sema, 0);
+
+	if (ret == WAIT_OBJECT_0)
+	{
+		/* We got it! */
+		return true;
+	}
+	else if (ret == WAIT_TIMEOUT)
+	{
+		/* Can't get it */
+		errno = EAGAIN;
+		return false;
+	}
+
+	/* Otherwise we are in trouble */
+	ereport(FATAL,
+			(errmsg("could not try-lock semaphore: error code %lu",
+					GetLastError())));
+
+	/* keep compiler quiet */
+	return false;
+}
diff --git a/src/backend/port/win32_shmem.c b/src/backend/port/win32_shmem.c
new file mode 100644
index 0000000..30b0730
--- /dev/null
+++ b/src/backend/port/win32_shmem.c
@@ -0,0 +1,599 @@
+/*-------------------------------------------------------------------------
+ *
+ * win32_shmem.c
+ *	  Implement shared memory using win32 facilities
+ *
+ * Portions Copyright (c) 1996-2020, PostgreSQL Global Development Group
+ *
+ * IDENTIFICATION
+ *	  src/backend/port/win32_shmem.c
+ *
+ *-------------------------------------------------------------------------
+ */
+#include "postgres.h"
+
+#include "miscadmin.h"
+#include "storage/dsm.h"
+#include "storage/ipc.h"
+#include "storage/pg_shmem.h"
+
+/*
+ * Early in a process's life, Windows asynchronously creates threads for the
+ * process's "default thread pool"
+ * (https://docs.microsoft.com/en-us/windows/desktop/ProcThread/thread-pools).
+ * Occasionally, thread creation allocates a stack after
+ * PGSharedMemoryReAttach() has released UsedShmemSegAddr and before it has
+ * mapped shared memory at UsedShmemSegAddr.  This would cause mapping to fail
+ * if the allocator preferred the just-released region for allocating the new
+ * thread stack.  We observed such failures in some Windows Server 2016
+ * configurations.  To give the system another region to prefer, reserve and
+ * release an additional, protective region immediately before reserving or
+ * releasing shared memory.  The idea is that, if the allocator handed out
+ * REGION1 pages before REGION2 pages at one occasion, it will do so whenever
+ * both regions are free.  Windows Server 2016 exhibits that behavior, and a
+ * system behaving differently would have less need to protect
+ * UsedShmemSegAddr.  The protective region must be at least large enough for
+ * one thread stack.  However, ten times as much is less than 2% of the 32-bit
+ * address space and is negligible relative to the 64-bit address space.
+ */
+#define PROTECTIVE_REGION_SIZE (10 * WIN32_STACK_RLIMIT)
+void	   *ShmemProtectiveRegion = NULL;
+
+HANDLE		UsedShmemSegID = INVALID_HANDLE_VALUE;
+void	   *UsedShmemSegAddr = NULL;
+static Size UsedShmemSegSize = 0;
+
+static bool EnableLockPagesPrivilege(int elevel);
+static void pgwin32_SharedMemoryDelete(int status, Datum shmId);
+
+/*
+ * Generate shared memory segment name. Expand the data directory, to generate
+ * an identifier unique for this data directory. Then replace all backslashes
+ * with forward slashes, since backslashes aren't permitted in global object names.
+ *
+ * Store the shared memory segment in the Global\ namespace (requires NT2 TSE or
+ * 2000, but that's all we support for other reasons as well), to make sure you can't
+ * open two postmasters in different sessions against the same data directory.
+ *
+ * XXX: What happens with junctions? It's only someone breaking things on purpose,
+ *		and this is still better than before, but we might want to do something about
+ *		that sometime in the future.
+ */
+static char *
+GetSharedMemName(void)
+{
+	char	   *retptr;
+	DWORD		bufsize;
+	DWORD		r;
+	char	   *cp;
+
+	bufsize = GetFullPathName(DataDir, 0, NULL, NULL);
+	if (bufsize == 0)
+		elog(FATAL, "could not get size for full pathname of datadir %s: error code %lu",
+			 DataDir, GetLastError());
+
+	retptr = malloc(bufsize + 18);	/* 18 for Global\PostgreSQL: */
+	if (retptr == NULL)
+		elog(FATAL, "could not allocate memory for shared memory name");
+
+	strcpy(retptr, "Global\\PostgreSQL:");
+	r = GetFullPathName(DataDir, bufsize, retptr + 18, NULL);
+	if (r == 0 || r > bufsize)
+		elog(FATAL, "could not generate full pathname for datadir %s: error code %lu",
+			 DataDir, GetLastError());
+
+	/*
+	 * XXX: Intentionally overwriting the Global\ part here. This was not the
+	 * original approach, but putting it in the actual Global\ namespace
+	 * causes permission errors in a lot of cases, so we leave it in the
+	 * default namespace for now.
+	 */
+	for (cp = retptr; *cp; cp++)
+		if (*cp == '\\')
+			*cp = '/';
+
+	return retptr;
+}
+
+
+/*
+ * PGSharedMemoryIsInUse
+ *
+ * Is a previously-existing shmem segment still existing and in use?
+ *
+ * The point of this exercise is to detect the case where a prior postmaster
+ * crashed, but it left child backends that are still running.  Therefore
+ * we only care about shmem segments that are associated with the intended
+ * DataDir.  This is an important consideration since accidental matches of
+ * shmem segment IDs are reasonably common.
+ */
+bool
+PGSharedMemoryIsInUse(unsigned long id1, unsigned long id2)
+{
+	char	   *szShareMem;
+	HANDLE		hmap;
+
+	szShareMem = GetSharedMemName();
+
+	hmap = OpenFileMapping(FILE_MAP_READ, FALSE, szShareMem);
+
+	free(szShareMem);
+
+	if (hmap == NULL)
+		return false;
+
+	CloseHandle(hmap);
+	return true;
+}
+
+/*
+ * EnableLockPagesPrivilege
+ *
+ * Try to acquire SeLockMemoryPrivilege so we can use large pages.
+ */
+static bool
+EnableLockPagesPrivilege(int elevel)
+{
+	HANDLE		hToken;
+	TOKEN_PRIVILEGES tp;
+	LUID		luid;
+
+	if (!OpenProcessToken(GetCurrentProcess(), TOKEN_ADJUST_PRIVILEGES | TOKEN_QUERY, &hToken))
+	{
+		ereport(elevel,
+				(errmsg("could not enable Lock Pages in Memory user right: error code %lu", GetLastError()),
+				 errdetail("Failed system call was %s.", "OpenProcessToken")));
+		return FALSE;
+	}
+
+	if (!LookupPrivilegeValue(NULL, SE_LOCK_MEMORY_NAME, &luid))
+	{
+		ereport(elevel,
+				(errmsg("could not enable Lock Pages in Memory user right: error code %lu", GetLastError()),
+				 errdetail("Failed system call was %s.", "LookupPrivilegeValue")));
+		CloseHandle(hToken);
+		return FALSE;
+	}
+	tp.PrivilegeCount = 1;
+	tp.Privileges[0].Luid = luid;
+	tp.Privileges[0].Attributes = SE_PRIVILEGE_ENABLED;
+
+	if (!AdjustTokenPrivileges(hToken, FALSE, &tp, 0, NULL, NULL))
+	{
+		ereport(elevel,
+				(errmsg("could not enable Lock Pages in Memory user right: error code %lu", GetLastError()),
+				 errdetail("Failed system call was %s.", "AdjustTokenPrivileges")));
+		CloseHandle(hToken);
+		return FALSE;
+	}
+
+	if (GetLastError() != ERROR_SUCCESS)
+	{
+		if (GetLastError() == ERROR_NOT_ALL_ASSIGNED)
+			ereport(elevel,
+					(errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
+					 errmsg("could not enable Lock Pages in Memory user right"),
+					 errhint("Assign Lock Pages in Memory user right to the Windows user account which runs PostgreSQL.")));
+		else
+			ereport(elevel,
+					(errmsg("could not enable Lock Pages in Memory user right: error code %lu", GetLastError()),
+					 errdetail("Failed system call was %s.", "AdjustTokenPrivileges")));
+		CloseHandle(hToken);
+		return FALSE;
+	}
+
+	CloseHandle(hToken);
+
+	return TRUE;
+}
+
+/*
+ * PGSharedMemoryCreate
+ *
+ * Create a shared memory segment of the given size and initialize its
+ * standard header.
+ */
+PGShmemHeader *
+PGSharedMemoryCreate(Size size,
+					 PGShmemHeader **shim)
+{
+	void	   *memAddress;
+	PGShmemHeader *hdr;
+	HANDLE		hmap,
+				hmap2;
+	char	   *szShareMem;
+	int			i;
+	DWORD		size_high;
+	DWORD		size_low;
+	SIZE_T		largePageSize = 0;
+	Size		orig_size = size;
+	DWORD		flProtect = PAGE_READWRITE;
+
+	ShmemProtectiveRegion = VirtualAlloc(NULL, PROTECTIVE_REGION_SIZE,
+										 MEM_RESERVE, PAGE_NOACCESS);
+	if (ShmemProtectiveRegion == NULL)
+		elog(FATAL, "could not reserve memory region: error code %lu",
+			 GetLastError());
+
+	/* Room for a header? */
+	Assert(size > MAXALIGN(sizeof(PGShmemHeader)));
+
+	szShareMem = GetSharedMemName();
+
+	UsedShmemSegAddr = NULL;
+
+	if (huge_pages == HUGE_PAGES_ON || huge_pages == HUGE_PAGES_TRY)
+	{
+		/* Does the processor support large pages? */
+		largePageSize = GetLargePageMinimum();
+		if (largePageSize == 0)
+		{
+			ereport(huge_pages == HUGE_PAGES_ON ? FATAL : DEBUG1,
+					(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+					 errmsg("the processor does not support large pages")));
+			ereport(DEBUG1,
+					(errmsg("disabling huge pages")));
+		}
+		else if (!EnableLockPagesPrivilege(huge_pages == HUGE_PAGES_ON ? FATAL : DEBUG1))
+		{
+			ereport(DEBUG1,
+					(errmsg("disabling huge pages")));
+		}
+		else
+		{
+			/* Huge pages available and privilege enabled, so turn on */
+			flProtect = PAGE_READWRITE | SEC_COMMIT | SEC_LARGE_PAGES;
+
+			/* Round size up as appropriate. */
+			if (size % largePageSize != 0)
+				size += largePageSize - (size % largePageSize);
+		}
+	}
+
+retry:
+#ifdef _WIN64
+	size_high = size >> 32;
+#else
+	size_high = 0;
+#endif
+	size_low = (DWORD) size;
+
+	/*
+	 * When recycling a shared memory segment, it may take a short while
+	 * before it gets dropped from the global namespace. So re-try after
+	 * sleeping for a second, and continue retrying 10 times. (both the 1
+	 * second time and the 10 retries are completely arbitrary)
+	 */
+	for (i = 0; i < 10; i++)
+	{
+		/*
+		 * In case CreateFileMapping() doesn't set the error code to 0 on
+		 * success
+		 */
+		SetLastError(0);
+
+		hmap = CreateFileMapping(INVALID_HANDLE_VALUE,	/* Use the pagefile */
+								 NULL,	/* Default security attrs */
+								 flProtect,
+								 size_high, /* Size Upper 32 Bits	*/
+								 size_low,	/* Size Lower 32 bits */
+								 szShareMem);
+
+		if (!hmap)
+		{
+			if (GetLastError() == ERROR_NO_SYSTEM_RESOURCES &&
+				huge_pages == HUGE_PAGES_TRY &&
+				(flProtect & SEC_LARGE_PAGES) != 0)
+			{
+				elog(DEBUG1, "CreateFileMapping(%zu) with SEC_LARGE_PAGES failed, "
+					 "huge pages disabled",
+					 size);
+
+				/*
+				 * Use the original size, not the rounded-up value, when
+				 * falling back to non-huge pages.
+				 */
+				size = orig_size;
+				flProtect = PAGE_READWRITE;
+				goto retry;
+			}
+			else
+				ereport(FATAL,
+						(errmsg("could not create shared memory segment: error code %lu", GetLastError()),
+						 errdetail("Failed system call was CreateFileMapping(size=%zu, name=%s).",
+								   size, szShareMem)));
+		}
+
+		/*
+		 * If the segment already existed, CreateFileMapping() will return a
+		 * handle to the existing one and set ERROR_ALREADY_EXISTS.
+		 */
+		if (GetLastError() == ERROR_ALREADY_EXISTS)
+		{
+			CloseHandle(hmap);	/* Close the handle, since we got a valid one
+								 * to the previous segment. */
+			hmap = NULL;
+			Sleep(1000);
+			continue;
+		}
+		break;
+	}
+
+	/*
+	 * If the last call in the loop still returned ERROR_ALREADY_EXISTS, this
+	 * shared memory segment exists and we assume it belongs to somebody else.
+	 */
+	if (!hmap)
+		ereport(FATAL,
+				(errmsg("pre-existing shared memory block is still in use"),
+				 errhint("Check if there are any old server processes still running, and terminate them.")));
+
+	free(szShareMem);
+
+	/*
+	 * Make the handle inheritable
+	 */
+	if (!DuplicateHandle(GetCurrentProcess(), hmap, GetCurrentProcess(), &hmap2, 0, TRUE, DUPLICATE_SAME_ACCESS))
+		ereport(FATAL,
+				(errmsg("could not create shared memory segment: error code %lu", GetLastError()),
+				 errdetail("Failed system call was DuplicateHandle.")));
+
+	/*
+	 * Close the old, non-inheritable handle. If this fails we don't really
+	 * care.
+	 */
+	if (!CloseHandle(hmap))
+		elog(LOG, "could not close handle to shared memory: error code %lu", GetLastError());
+
+
+	/*
+	 * Get a pointer to the new shared memory segment. Map the whole segment
+	 * at once, and let the system decide on the initial address.
+	 */
+	memAddress = MapViewOfFileEx(hmap2, FILE_MAP_WRITE | FILE_MAP_READ, 0, 0, 0, NULL);
+	if (!memAddress)
+		ereport(FATAL,
+				(errmsg("could not create shared memory segment: error code %lu", GetLastError()),
+				 errdetail("Failed system call was MapViewOfFileEx.")));
+
+
+
+	/*
+	 * OK, we created a new segment.  Mark it as created by this process. The
+	 * order of assignments here is critical so that another Postgres process
+	 * can't see the header as valid but belonging to an invalid PID!
+	 */
+	hdr = (PGShmemHeader *) memAddress;
+	hdr->creatorPID = getpid();
+	hdr->magic = PGShmemMagic;
+
+	/*
+	 * Initialize space allocation status for segment.
+	 */
+	hdr->totalsize = size;
+	hdr->freeoffset = MAXALIGN(sizeof(PGShmemHeader));
+	hdr->dsm_control = 0;
+
+	/* Save info for possible future use */
+	UsedShmemSegAddr = memAddress;
+	UsedShmemSegSize = size;
+	UsedShmemSegID = hmap2;
+
+	/* Register on-exit routine to delete the new segment */
+	on_shmem_exit(pgwin32_SharedMemoryDelete, PointerGetDatum(hmap2));
+
+	*shim = hdr;
+	return hdr;
+}
+
+/*
+ * PGSharedMemoryReAttach
+ *
+ * This is called during startup of a postmaster child process to re-attach to
+ * an already existing shared memory segment, using the handle inherited from
+ * the postmaster.
+ *
+ * ShmemProtectiveRegion, UsedShmemSegID and UsedShmemSegAddr are implicit
+ * parameters to this routine.  The caller must have already restored them to
+ * the postmaster's values.
+ */
+void
+PGSharedMemoryReAttach(void)
+{
+	PGShmemHeader *hdr;
+	void	   *origUsedShmemSegAddr = UsedShmemSegAddr;
+
+	Assert(ShmemProtectiveRegion != NULL);
+	Assert(UsedShmemSegAddr != NULL);
+	Assert(IsUnderPostmaster);
+
+	/*
+	 * Release memory region reservations made by the postmaster
+	 */
+	if (VirtualFree(ShmemProtectiveRegion, 0, MEM_RELEASE) == 0)
+		elog(FATAL, "failed to release reserved memory region (addr=%p): error code %lu",
+			 ShmemProtectiveRegion, GetLastError());
+	if (VirtualFree(UsedShmemSegAddr, 0, MEM_RELEASE) == 0)
+		elog(FATAL, "failed to release reserved memory region (addr=%p): error code %lu",
+			 UsedShmemSegAddr, GetLastError());
+
+	hdr = (PGShmemHeader *) MapViewOfFileEx(UsedShmemSegID, FILE_MAP_READ | FILE_MAP_WRITE, 0, 0, 0, UsedShmemSegAddr);
+	if (!hdr)
+		elog(FATAL, "could not reattach to shared memory (key=%p, addr=%p): error code %lu",
+			 UsedShmemSegID, UsedShmemSegAddr, GetLastError());
+	if (hdr != origUsedShmemSegAddr)
+		elog(FATAL, "reattaching to shared memory returned unexpected address (got %p, expected %p)",
+			 hdr, origUsedShmemSegAddr);
+	if (hdr->magic != PGShmemMagic)
+		elog(FATAL, "reattaching to shared memory returned non-PostgreSQL memory");
+	dsm_set_control_handle(hdr->dsm_control);
+
+	UsedShmemSegAddr = hdr;		/* probably redundant */
+}
+
+/*
+ * PGSharedMemoryNoReAttach
+ *
+ * This is called during startup of a postmaster child process when we choose
+ * *not* to re-attach to the existing shared memory segment.  We must clean up
+ * to leave things in the appropriate state.
+ *
+ * The child process startup logic might or might not call PGSharedMemoryDetach
+ * after this; make sure that it will be a no-op if called.
+ *
+ * ShmemProtectiveRegion, UsedShmemSegID and UsedShmemSegAddr are implicit
+ * parameters to this routine.  The caller must have already restored them to
+ * the postmaster's values.
+ */
+void
+PGSharedMemoryNoReAttach(void)
+{
+	Assert(ShmemProtectiveRegion != NULL);
+	Assert(UsedShmemSegAddr != NULL);
+	Assert(IsUnderPostmaster);
+
+	/*
+	 * Under Windows we will not have mapped the segment, so we don't need to
+	 * un-map it.  Just reset UsedShmemSegAddr to show we're not attached.
+	 */
+	UsedShmemSegAddr = NULL;
+
+	/*
+	 * We *must* close the inherited shmem segment handle, else Windows will
+	 * consider the existence of this process to mean it can't release the
+	 * shmem segment yet.  We can now use PGSharedMemoryDetach to do that.
+	 */
+	PGSharedMemoryDetach();
+}
+
+/*
+ * PGSharedMemoryDetach
+ *
+ * Detach from the shared memory segment, if still attached.  This is not
+ * intended to be called explicitly by the process that originally created the
+ * segment (it will have an on_shmem_exit callback registered to do that).
+ * Rather, this is for subprocesses that have inherited an attachment and want
+ * to get rid of it.
+ *
+ * ShmemProtectiveRegion, UsedShmemSegID and UsedShmemSegAddr are implicit
+ * parameters to this routine.
+ */
+void
+PGSharedMemoryDetach(void)
+{
+	/*
+	 * Releasing the protective region liberates an unimportant quantity of
+	 * address space, but be tidy.
+	 */
+	if (ShmemProtectiveRegion != NULL)
+	{
+		if (VirtualFree(ShmemProtectiveRegion, 0, MEM_RELEASE) == 0)
+			elog(LOG, "failed to release reserved memory region (addr=%p): error code %lu",
+				 ShmemProtectiveRegion, GetLastError());
+
+		ShmemProtectiveRegion = NULL;
+	}
+
+	/* Unmap the view, if it's mapped */
+	if (UsedShmemSegAddr != NULL)
+	{
+		if (!UnmapViewOfFile(UsedShmemSegAddr))
+			elog(LOG, "could not unmap view of shared memory: error code %lu",
+				 GetLastError());
+
+		UsedShmemSegAddr = NULL;
+	}
+
+	/* And close the shmem handle, if we have one */
+	if (UsedShmemSegID != INVALID_HANDLE_VALUE)
+	{
+		if (!CloseHandle(UsedShmemSegID))
+			elog(LOG, "could not close handle to shared memory: error code %lu",
+				 GetLastError());
+
+		UsedShmemSegID = INVALID_HANDLE_VALUE;
+	}
+}
+
+
+/*
+ * pgwin32_SharedMemoryDelete
+ *
+ * Detach from and delete the shared memory segment
+ * (called as an on_shmem_exit callback, hence funny argument list)
+ */
+static void
+pgwin32_SharedMemoryDelete(int status, Datum shmId)
+{
+	Assert(DatumGetPointer(shmId) == UsedShmemSegID);
+	PGSharedMemoryDetach();
+}
+
+/*
+ * pgwin32_ReserveSharedMemoryRegion(hChild)
+ *
+ * Reserve the memory region that will be used for shared memory in a child
+ * process. It is called before the child process starts, to make sure the
+ * memory is available.
+ *
+ * Once the child starts, DLLs loading in different order or threads getting
+ * scheduled differently may allocate memory which can conflict with the
+ * address space we need for our shared memory. By reserving the shared
+ * memory region before the child starts, and freeing it only just before we
+ * attempt to get access to the shared memory forces these allocations to
+ * be given different address ranges that don't conflict.
+ *
+ * NOTE! This function executes in the postmaster, and should for this
+ * reason not use elog(FATAL) since that would take down the postmaster.
+ */
+int
+pgwin32_ReserveSharedMemoryRegion(HANDLE hChild)
+{
+	void	   *address;
+
+	Assert(ShmemProtectiveRegion != NULL);
+	Assert(UsedShmemSegAddr != NULL);
+	Assert(UsedShmemSegSize != 0);
+
+	/* ShmemProtectiveRegion */
+	address = VirtualAllocEx(hChild, ShmemProtectiveRegion,
+							 PROTECTIVE_REGION_SIZE,
+							 MEM_RESERVE, PAGE_NOACCESS);
+	if (address == NULL)
+	{
+		/* Don't use FATAL since we're running in the postmaster */
+		elog(LOG, "could not reserve shared memory region (addr=%p) for child %p: error code %lu",
+			 ShmemProtectiveRegion, hChild, GetLastError());
+		return false;
+	}
+	if (address != ShmemProtectiveRegion)
+	{
+		/*
+		 * Should never happen - in theory if allocation granularity causes
+		 * strange effects it could, so check just in case.
+		 *
+		 * Don't use FATAL since we're running in the postmaster.
+		 */
+		elog(LOG, "reserved shared memory region got incorrect address %p, expected %p",
+			 address, ShmemProtectiveRegion);
+		return false;
+	}
+
+	/* UsedShmemSegAddr */
+	address = VirtualAllocEx(hChild, UsedShmemSegAddr, UsedShmemSegSize,
+							 MEM_RESERVE, PAGE_READWRITE);
+	if (address == NULL)
+	{
+		elog(LOG, "could not reserve shared memory region (addr=%p) for child %p: error code %lu",
+			 UsedShmemSegAddr, hChild, GetLastError());
+		return false;
+	}
+	if (address != UsedShmemSegAddr)
+	{
+		elog(LOG, "reserved shared memory region got incorrect address %p, expected %p",
+			 address, UsedShmemSegAddr);
+		return false;
+	}
+
+	return true;
+}