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Diffstat (limited to 'src/backend/storage/ipc/latch.c')
| -rw-r--r-- | src/backend/storage/ipc/latch.c | 2268 |
1 files changed, 2268 insertions, 0 deletions
diff --git a/src/backend/storage/ipc/latch.c b/src/backend/storage/ipc/latch.c new file mode 100644 index 0000000..cdb95c1 --- /dev/null +++ b/src/backend/storage/ipc/latch.c @@ -0,0 +1,2268 @@ +/*------------------------------------------------------------------------- + * + * latch.c + * Routines for inter-process latches + * + * The poll() implementation uses the so-called self-pipe trick to overcome the + * race condition involved with poll() and setting a global flag in the signal + * handler. When a latch is set and the current process is waiting for it, the + * signal handler wakes up the poll() in WaitLatch by writing a byte to a pipe. + * A signal by itself doesn't interrupt poll() on all platforms, and even on + * platforms where it does, a signal that arrives just before the poll() call + * does not prevent poll() from entering sleep. An incoming byte on a pipe + * however reliably interrupts the sleep, and causes poll() to return + * immediately even if the signal arrives before poll() begins. + * + * The epoll() implementation overcomes the race with a different technique: it + * keeps SIGURG blocked and consumes from a signalfd() descriptor instead. We + * don't need to register a signal handler or create our own self-pipe. We + * assume that any system that has Linux epoll() also has Linux signalfd(). + * + * The kqueue() implementation waits for SIGURG with EVFILT_SIGNAL. + * + * The Windows implementation uses Windows events that are inherited by all + * postmaster child processes. There's no need for the self-pipe trick there. + * + * Portions Copyright (c) 1996-2023, PostgreSQL Global Development Group + * Portions Copyright (c) 1994, Regents of the University of California + * + * IDENTIFICATION + * src/backend/storage/ipc/latch.c + * + *------------------------------------------------------------------------- + */ +#include "postgres.h" + +#include <fcntl.h> +#include <limits.h> +#include <signal.h> +#include <unistd.h> +#ifdef HAVE_SYS_EPOLL_H +#include <sys/epoll.h> +#endif +#ifdef HAVE_SYS_EVENT_H +#include <sys/event.h> +#endif +#ifdef HAVE_SYS_SIGNALFD_H +#include <sys/signalfd.h> +#endif +#ifdef HAVE_POLL_H +#include <poll.h> +#endif + +#include "libpq/pqsignal.h" +#include "miscadmin.h" +#include "pgstat.h" +#include "port/atomics.h" +#include "portability/instr_time.h" +#include "postmaster/postmaster.h" +#include "storage/fd.h" +#include "storage/ipc.h" +#include "storage/latch.h" +#include "storage/pmsignal.h" +#include "storage/shmem.h" +#include "utils/memutils.h" + +/* + * Select the fd readiness primitive to use. Normally the "most modern" + * primitive supported by the OS will be used, but for testing it can be + * useful to manually specify the used primitive. If desired, just add a + * define somewhere before this block. + */ +#if defined(WAIT_USE_EPOLL) || defined(WAIT_USE_POLL) || \ + defined(WAIT_USE_KQUEUE) || defined(WAIT_USE_WIN32) +/* don't overwrite manual choice */ +#elif defined(HAVE_SYS_EPOLL_H) +#define WAIT_USE_EPOLL +#elif defined(HAVE_KQUEUE) +#define WAIT_USE_KQUEUE +#elif defined(HAVE_POLL) +#define WAIT_USE_POLL +#elif WIN32 +#define WAIT_USE_WIN32 +#else +#error "no wait set implementation available" +#endif + +/* + * By default, we use a self-pipe with poll() and a signalfd with epoll(), if + * available. We avoid signalfd on illumos for now based on problem reports. + * For testing the choice can also be manually specified. + */ +#if defined(WAIT_USE_POLL) || defined(WAIT_USE_EPOLL) +#if defined(WAIT_USE_SELF_PIPE) || defined(WAIT_USE_SIGNALFD) +/* don't overwrite manual choice */ +#elif defined(WAIT_USE_EPOLL) && defined(HAVE_SYS_SIGNALFD_H) && \ + !defined(__illumos__) +#define WAIT_USE_SIGNALFD +#else +#define WAIT_USE_SELF_PIPE +#endif +#endif + +/* typedef in latch.h */ +struct WaitEventSet +{ + int nevents; /* number of registered events */ + int nevents_space; /* maximum number of events in this set */ + + /* + * Array, of nevents_space length, storing the definition of events this + * set is waiting for. + */ + WaitEvent *events; + + /* + * If WL_LATCH_SET is specified in any wait event, latch is a pointer to + * said latch, and latch_pos the offset in the ->events array. This is + * useful because we check the state of the latch before performing doing + * syscalls related to waiting. + */ + Latch *latch; + int latch_pos; + + /* + * WL_EXIT_ON_PM_DEATH is converted to WL_POSTMASTER_DEATH, but this flag + * is set so that we'll exit immediately if postmaster death is detected, + * instead of returning. + */ + bool exit_on_postmaster_death; + +#if defined(WAIT_USE_EPOLL) + int epoll_fd; + /* epoll_wait returns events in a user provided arrays, allocate once */ + struct epoll_event *epoll_ret_events; +#elif defined(WAIT_USE_KQUEUE) + int kqueue_fd; + /* kevent returns events in a user provided arrays, allocate once */ + struct kevent *kqueue_ret_events; + bool report_postmaster_not_running; +#elif defined(WAIT_USE_POLL) + /* poll expects events to be waited on every poll() call, prepare once */ + struct pollfd *pollfds; +#elif defined(WAIT_USE_WIN32) + + /* + * Array of windows events. The first element always contains + * pgwin32_signal_event, so the remaining elements are offset by one (i.e. + * event->pos + 1). + */ + HANDLE *handles; +#endif +}; + +/* A common WaitEventSet used to implement WaitLatch() */ +static WaitEventSet *LatchWaitSet; + +/* The position of the latch in LatchWaitSet. */ +#define LatchWaitSetLatchPos 0 + +#ifndef WIN32 +/* Are we currently in WaitLatch? The signal handler would like to know. */ +static volatile sig_atomic_t waiting = false; +#endif + +#ifdef WAIT_USE_SIGNALFD +/* On Linux, we'll receive SIGURG via a signalfd file descriptor. */ +static int signal_fd = -1; +#endif + +#ifdef WAIT_USE_SELF_PIPE +/* Read and write ends of the self-pipe */ +static int selfpipe_readfd = -1; +static int selfpipe_writefd = -1; + +/* Process owning the self-pipe --- needed for checking purposes */ +static int selfpipe_owner_pid = 0; + +/* Private function prototypes */ +static void latch_sigurg_handler(SIGNAL_ARGS); +static void sendSelfPipeByte(void); +#endif + +#if defined(WAIT_USE_SELF_PIPE) || defined(WAIT_USE_SIGNALFD) +static void drain(void); +#endif + +#if defined(WAIT_USE_EPOLL) +static void WaitEventAdjustEpoll(WaitEventSet *set, WaitEvent *event, int action); +#elif defined(WAIT_USE_KQUEUE) +static void WaitEventAdjustKqueue(WaitEventSet *set, WaitEvent *event, int old_events); +#elif defined(WAIT_USE_POLL) +static void WaitEventAdjustPoll(WaitEventSet *set, WaitEvent *event); +#elif defined(WAIT_USE_WIN32) +static void WaitEventAdjustWin32(WaitEventSet *set, WaitEvent *event); +#endif + +static inline int WaitEventSetWaitBlock(WaitEventSet *set, int cur_timeout, + WaitEvent *occurred_events, int nevents); + +/* + * Initialize the process-local latch infrastructure. + * + * This must be called once during startup of any process that can wait on + * latches, before it issues any InitLatch() or OwnLatch() calls. + */ +void +InitializeLatchSupport(void) +{ +#if defined(WAIT_USE_SELF_PIPE) + int pipefd[2]; + + if (IsUnderPostmaster) + { + /* + * We might have inherited connections to a self-pipe created by the + * postmaster. It's critical that child processes create their own + * self-pipes, of course, and we really want them to close the + * inherited FDs for safety's sake. + */ + if (selfpipe_owner_pid != 0) + { + /* Assert we go through here but once in a child process */ + Assert(selfpipe_owner_pid != MyProcPid); + /* Release postmaster's pipe FDs; ignore any error */ + (void) close(selfpipe_readfd); + (void) close(selfpipe_writefd); + /* Clean up, just for safety's sake; we'll set these below */ + selfpipe_readfd = selfpipe_writefd = -1; + selfpipe_owner_pid = 0; + /* Keep fd.c's accounting straight */ + ReleaseExternalFD(); + ReleaseExternalFD(); + } + else + { + /* + * Postmaster didn't create a self-pipe ... or else we're in an + * EXEC_BACKEND build, in which case it doesn't matter since the + * postmaster's pipe FDs were closed by the action of FD_CLOEXEC. + * fd.c won't have state to clean up, either. + */ + Assert(selfpipe_readfd == -1); + } + } + else + { + /* In postmaster or standalone backend, assert we do this but once */ + Assert(selfpipe_readfd == -1); + Assert(selfpipe_owner_pid == 0); + } + + /* + * Set up the self-pipe that allows a signal handler to wake up the + * poll()/epoll_wait() in WaitLatch. Make the write-end non-blocking, so + * that SetLatch won't block if the event has already been set many times + * filling the kernel buffer. Make the read-end non-blocking too, so that + * we can easily clear the pipe by reading until EAGAIN or EWOULDBLOCK. + * Also, make both FDs close-on-exec, since we surely do not want any + * child processes messing with them. + */ + if (pipe(pipefd) < 0) + elog(FATAL, "pipe() failed: %m"); + if (fcntl(pipefd[0], F_SETFL, O_NONBLOCK) == -1) + elog(FATAL, "fcntl(F_SETFL) failed on read-end of self-pipe: %m"); + if (fcntl(pipefd[1], F_SETFL, O_NONBLOCK) == -1) + elog(FATAL, "fcntl(F_SETFL) failed on write-end of self-pipe: %m"); + if (fcntl(pipefd[0], F_SETFD, FD_CLOEXEC) == -1) + elog(FATAL, "fcntl(F_SETFD) failed on read-end of self-pipe: %m"); + if (fcntl(pipefd[1], F_SETFD, FD_CLOEXEC) == -1) + elog(FATAL, "fcntl(F_SETFD) failed on write-end of self-pipe: %m"); + + selfpipe_readfd = pipefd[0]; + selfpipe_writefd = pipefd[1]; + selfpipe_owner_pid = MyProcPid; + + /* Tell fd.c about these two long-lived FDs */ + ReserveExternalFD(); + ReserveExternalFD(); + + pqsignal(SIGURG, latch_sigurg_handler); +#endif + +#ifdef WAIT_USE_SIGNALFD + sigset_t signalfd_mask; + + if (IsUnderPostmaster) + { + /* + * It would probably be safe to re-use the inherited signalfd since + * signalfds only see the current process's pending signals, but it + * seems less surprising to close it and create our own. + */ + if (signal_fd != -1) + { + /* Release postmaster's signal FD; ignore any error */ + (void) close(signal_fd); + signal_fd = -1; + ReleaseExternalFD(); + } + } + + /* Block SIGURG, because we'll receive it through a signalfd. */ + sigaddset(&UnBlockSig, SIGURG); + + /* Set up the signalfd to receive SIGURG notifications. */ + sigemptyset(&signalfd_mask); + sigaddset(&signalfd_mask, SIGURG); + signal_fd = signalfd(-1, &signalfd_mask, SFD_NONBLOCK | SFD_CLOEXEC); + if (signal_fd < 0) + elog(FATAL, "signalfd() failed"); + ReserveExternalFD(); +#endif + +#ifdef WAIT_USE_KQUEUE + /* Ignore SIGURG, because we'll receive it via kqueue. */ + pqsignal(SIGURG, SIG_IGN); +#endif +} + +void +InitializeLatchWaitSet(void) +{ + int latch_pos PG_USED_FOR_ASSERTS_ONLY; + + Assert(LatchWaitSet == NULL); + + /* Set up the WaitEventSet used by WaitLatch(). */ + LatchWaitSet = CreateWaitEventSet(TopMemoryContext, 2); + latch_pos = AddWaitEventToSet(LatchWaitSet, WL_LATCH_SET, PGINVALID_SOCKET, + MyLatch, NULL); + if (IsUnderPostmaster) + AddWaitEventToSet(LatchWaitSet, WL_EXIT_ON_PM_DEATH, + PGINVALID_SOCKET, NULL, NULL); + + Assert(latch_pos == LatchWaitSetLatchPos); +} + +void +ShutdownLatchSupport(void) +{ +#if defined(WAIT_USE_POLL) + pqsignal(SIGURG, SIG_IGN); +#endif + + if (LatchWaitSet) + { + FreeWaitEventSet(LatchWaitSet); + LatchWaitSet = NULL; + } + +#if defined(WAIT_USE_SELF_PIPE) + close(selfpipe_readfd); + close(selfpipe_writefd); + selfpipe_readfd = -1; + selfpipe_writefd = -1; + selfpipe_owner_pid = InvalidPid; +#endif + +#if defined(WAIT_USE_SIGNALFD) + close(signal_fd); + signal_fd = -1; +#endif +} + +/* + * Initialize a process-local latch. + */ +void +InitLatch(Latch *latch) +{ + latch->is_set = false; + latch->maybe_sleeping = false; + latch->owner_pid = MyProcPid; + latch->is_shared = false; + +#if defined(WAIT_USE_SELF_PIPE) + /* Assert InitializeLatchSupport has been called in this process */ + Assert(selfpipe_readfd >= 0 && selfpipe_owner_pid == MyProcPid); +#elif defined(WAIT_USE_SIGNALFD) + /* Assert InitializeLatchSupport has been called in this process */ + Assert(signal_fd >= 0); +#elif defined(WAIT_USE_WIN32) + latch->event = CreateEvent(NULL, TRUE, FALSE, NULL); + if (latch->event == NULL) + elog(ERROR, "CreateEvent failed: error code %lu", GetLastError()); +#endif /* WIN32 */ +} + +/* + * Initialize a shared latch that can be set from other processes. The latch + * is initially owned by no-one; use OwnLatch to associate it with the + * current process. + * + * InitSharedLatch needs to be called in postmaster before forking child + * processes, usually right after allocating the shared memory block + * containing the latch with ShmemInitStruct. (The Unix implementation + * doesn't actually require that, but the Windows one does.) Because of + * this restriction, we have no concurrency issues to worry about here. + * + * Note that other handles created in this module are never marked as + * inheritable. Thus we do not need to worry about cleaning up child + * process references to postmaster-private latches or WaitEventSets. + */ +void +InitSharedLatch(Latch *latch) +{ +#ifdef WIN32 + SECURITY_ATTRIBUTES sa; + + /* + * Set up security attributes to specify that the events are inherited. + */ + ZeroMemory(&sa, sizeof(sa)); + sa.nLength = sizeof(sa); + sa.bInheritHandle = TRUE; + + latch->event = CreateEvent(&sa, TRUE, FALSE, NULL); + if (latch->event == NULL) + elog(ERROR, "CreateEvent failed: error code %lu", GetLastError()); +#endif + + latch->is_set = false; + latch->maybe_sleeping = false; + latch->owner_pid = 0; + latch->is_shared = true; +} + +/* + * Associate a shared latch with the current process, allowing it to + * wait on the latch. + * + * Although there is a sanity check for latch-already-owned, we don't do + * any sort of locking here, meaning that we could fail to detect the error + * if two processes try to own the same latch at about the same time. If + * there is any risk of that, caller must provide an interlock to prevent it. + */ +void +OwnLatch(Latch *latch) +{ + int owner_pid; + + /* Sanity checks */ + Assert(latch->is_shared); + +#if defined(WAIT_USE_SELF_PIPE) + /* Assert InitializeLatchSupport has been called in this process */ + Assert(selfpipe_readfd >= 0 && selfpipe_owner_pid == MyProcPid); +#elif defined(WAIT_USE_SIGNALFD) + /* Assert InitializeLatchSupport has been called in this process */ + Assert(signal_fd >= 0); +#endif + + owner_pid = latch->owner_pid; + if (owner_pid != 0) + elog(PANIC, "latch already owned by PID %d", owner_pid); + + latch->owner_pid = MyProcPid; +} + +/* + * Disown a shared latch currently owned by the current process. + */ +void +DisownLatch(Latch *latch) +{ + Assert(latch->is_shared); + Assert(latch->owner_pid == MyProcPid); + + latch->owner_pid = 0; +} + +/* + * Wait for a given latch to be set, or for postmaster death, or until timeout + * is exceeded. 'wakeEvents' is a bitmask that specifies which of those events + * to wait for. If the latch is already set (and WL_LATCH_SET is given), the + * function returns immediately. + * + * The "timeout" is given in milliseconds. It must be >= 0 if WL_TIMEOUT flag + * is given. Although it is declared as "long", we don't actually support + * timeouts longer than INT_MAX milliseconds. Note that some extra overhead + * is incurred when WL_TIMEOUT is given, so avoid using a timeout if possible. + * + * The latch must be owned by the current process, ie. it must be a + * process-local latch initialized with InitLatch, or a shared latch + * associated with the current process by calling OwnLatch. + * + * Returns bit mask indicating which condition(s) caused the wake-up. Note + * that if multiple wake-up conditions are true, there is no guarantee that + * we return all of them in one call, but we will return at least one. + */ +int +WaitLatch(Latch *latch, int wakeEvents, long timeout, + uint32 wait_event_info) +{ + WaitEvent event; + + /* Postmaster-managed callers must handle postmaster death somehow. */ + Assert(!IsUnderPostmaster || + (wakeEvents & WL_EXIT_ON_PM_DEATH) || + (wakeEvents & WL_POSTMASTER_DEATH)); + + /* + * Some callers may have a latch other than MyLatch, or no latch at all, + * or want to handle postmaster death differently. It's cheap to assign + * those, so just do it every time. + */ + if (!(wakeEvents & WL_LATCH_SET)) + latch = NULL; + ModifyWaitEvent(LatchWaitSet, LatchWaitSetLatchPos, WL_LATCH_SET, latch); + LatchWaitSet->exit_on_postmaster_death = + ((wakeEvents & WL_EXIT_ON_PM_DEATH) != 0); + + if (WaitEventSetWait(LatchWaitSet, + (wakeEvents & WL_TIMEOUT) ? timeout : -1, + &event, 1, + wait_event_info) == 0) + return WL_TIMEOUT; + else + return event.events; +} + +/* + * Like WaitLatch, but with an extra socket argument for WL_SOCKET_* + * conditions. + * + * When waiting on a socket, EOF and error conditions always cause the socket + * to be reported as readable/writable/connected, so that the caller can deal + * with the condition. + * + * wakeEvents must include either WL_EXIT_ON_PM_DEATH for automatic exit + * if the postmaster dies or WL_POSTMASTER_DEATH for a flag set in the + * return value if the postmaster dies. The latter is useful for rare cases + * where some behavior other than immediate exit is needed. + * + * NB: These days this is just a wrapper around the WaitEventSet API. When + * using a latch very frequently, consider creating a longer living + * WaitEventSet instead; that's more efficient. + */ +int +WaitLatchOrSocket(Latch *latch, int wakeEvents, pgsocket sock, + long timeout, uint32 wait_event_info) +{ + int ret = 0; + int rc; + WaitEvent event; + WaitEventSet *set = CreateWaitEventSet(CurrentMemoryContext, 3); + + if (wakeEvents & WL_TIMEOUT) + Assert(timeout >= 0); + else + timeout = -1; + + if (wakeEvents & WL_LATCH_SET) + AddWaitEventToSet(set, WL_LATCH_SET, PGINVALID_SOCKET, + latch, NULL); + + /* Postmaster-managed callers must handle postmaster death somehow. */ + Assert(!IsUnderPostmaster || + (wakeEvents & WL_EXIT_ON_PM_DEATH) || + (wakeEvents & WL_POSTMASTER_DEATH)); + + if ((wakeEvents & WL_POSTMASTER_DEATH) && IsUnderPostmaster) + AddWaitEventToSet(set, WL_POSTMASTER_DEATH, PGINVALID_SOCKET, + NULL, NULL); + + if ((wakeEvents & WL_EXIT_ON_PM_DEATH) && IsUnderPostmaster) + AddWaitEventToSet(set, WL_EXIT_ON_PM_DEATH, PGINVALID_SOCKET, + NULL, NULL); + + if (wakeEvents & WL_SOCKET_MASK) + { + int ev; + + ev = wakeEvents & WL_SOCKET_MASK; + AddWaitEventToSet(set, ev, sock, NULL, NULL); + } + + rc = WaitEventSetWait(set, timeout, &event, 1, wait_event_info); + + if (rc == 0) + ret |= WL_TIMEOUT; + else + { + ret |= event.events & (WL_LATCH_SET | + WL_POSTMASTER_DEATH | + WL_SOCKET_MASK); + } + + FreeWaitEventSet(set); + + return ret; +} + +/* + * Sets a latch and wakes up anyone waiting on it. + * + * This is cheap if the latch is already set, otherwise not so much. + * + * NB: when calling this in a signal handler, be sure to save and restore + * errno around it. (That's standard practice in most signal handlers, of + * course, but we used to omit it in handlers that only set a flag.) + * + * NB: this function is called from critical sections and signal handlers so + * throwing an error is not a good idea. + */ +void +SetLatch(Latch *latch) +{ +#ifndef WIN32 + pid_t owner_pid; +#else + HANDLE handle; +#endif + + /* + * The memory barrier has to be placed here to ensure that any flag + * variables possibly changed by this process have been flushed to main + * memory, before we check/set is_set. + */ + pg_memory_barrier(); + + /* Quick exit if already set */ + if (latch->is_set) + return; + + latch->is_set = true; + + pg_memory_barrier(); + if (!latch->maybe_sleeping) + return; + +#ifndef WIN32 + + /* + * See if anyone's waiting for the latch. It can be the current process if + * we're in a signal handler. We use the self-pipe or SIGURG to ourselves + * to wake up WaitEventSetWaitBlock() without races in that case. If it's + * another process, send a signal. + * + * Fetch owner_pid only once, in case the latch is concurrently getting + * owned or disowned. XXX: This assumes that pid_t is atomic, which isn't + * guaranteed to be true! In practice, the effective range of pid_t fits + * in a 32 bit integer, and so should be atomic. In the worst case, we + * might end up signaling the wrong process. Even then, you're very + * unlucky if a process with that bogus pid exists and belongs to + * Postgres; and PG database processes should handle excess SIGUSR1 + * interrupts without a problem anyhow. + * + * Another sort of race condition that's possible here is for a new + * process to own the latch immediately after we look, so we don't signal + * it. This is okay so long as all callers of ResetLatch/WaitLatch follow + * the standard coding convention of waiting at the bottom of their loops, + * not the top, so that they'll correctly process latch-setting events + * that happen before they enter the loop. + */ + owner_pid = latch->owner_pid; + if (owner_pid == 0) + return; + else if (owner_pid == MyProcPid) + { +#if defined(WAIT_USE_SELF_PIPE) + if (waiting) + sendSelfPipeByte(); +#else + if (waiting) + kill(MyProcPid, SIGURG); +#endif + } + else + kill(owner_pid, SIGURG); + +#else + + /* + * See if anyone's waiting for the latch. It can be the current process if + * we're in a signal handler. + * + * Use a local variable here just in case somebody changes the event field + * concurrently (which really should not happen). + */ + handle = latch->event; + if (handle) + { + SetEvent(handle); + + /* + * Note that we silently ignore any errors. We might be in a signal + * handler or other critical path where it's not safe to call elog(). + */ + } +#endif +} + +/* + * Clear the latch. Calling WaitLatch after this will sleep, unless + * the latch is set again before the WaitLatch call. + */ +void +ResetLatch(Latch *latch) +{ + /* Only the owner should reset the latch */ + Assert(latch->owner_pid == MyProcPid); + Assert(latch->maybe_sleeping == false); + + latch->is_set = false; + + /* + * Ensure that the write to is_set gets flushed to main memory before we + * examine any flag variables. Otherwise a concurrent SetLatch might + * falsely conclude that it needn't signal us, even though we have missed + * seeing some flag updates that SetLatch was supposed to inform us of. + */ + pg_memory_barrier(); +} + +/* + * Create a WaitEventSet with space for nevents different events to wait for. + * + * These events can then be efficiently waited upon together, using + * WaitEventSetWait(). + */ +WaitEventSet * +CreateWaitEventSet(MemoryContext context, int nevents) +{ + WaitEventSet *set; + char *data; + Size sz = 0; + + /* + * Use MAXALIGN size/alignment to guarantee that later uses of memory are + * aligned correctly. E.g. epoll_event might need 8 byte alignment on some + * platforms, but earlier allocations like WaitEventSet and WaitEvent + * might not be sized to guarantee that when purely using sizeof(). + */ + sz += MAXALIGN(sizeof(WaitEventSet)); + sz += MAXALIGN(sizeof(WaitEvent) * nevents); + +#if defined(WAIT_USE_EPOLL) + sz += MAXALIGN(sizeof(struct epoll_event) * nevents); +#elif defined(WAIT_USE_KQUEUE) + sz += MAXALIGN(sizeof(struct kevent) * nevents); +#elif defined(WAIT_USE_POLL) + sz += MAXALIGN(sizeof(struct pollfd) * nevents); +#elif defined(WAIT_USE_WIN32) + /* need space for the pgwin32_signal_event */ + sz += MAXALIGN(sizeof(HANDLE) * (nevents + 1)); +#endif + + data = (char *) MemoryContextAllocZero(context, sz); + + set = (WaitEventSet *) data; + data += MAXALIGN(sizeof(WaitEventSet)); + + set->events = (WaitEvent *) data; + data += MAXALIGN(sizeof(WaitEvent) * nevents); + +#if defined(WAIT_USE_EPOLL) + set->epoll_ret_events = (struct epoll_event *) data; + data += MAXALIGN(sizeof(struct epoll_event) * nevents); +#elif defined(WAIT_USE_KQUEUE) + set->kqueue_ret_events = (struct kevent *) data; + data += MAXALIGN(sizeof(struct kevent) * nevents); +#elif defined(WAIT_USE_POLL) + set->pollfds = (struct pollfd *) data; + data += MAXALIGN(sizeof(struct pollfd) * nevents); +#elif defined(WAIT_USE_WIN32) + set->handles = (HANDLE) data; + data += MAXALIGN(sizeof(HANDLE) * nevents); +#endif + + set->latch = NULL; + set->nevents_space = nevents; + set->exit_on_postmaster_death = false; + +#if defined(WAIT_USE_EPOLL) + if (!AcquireExternalFD()) + { + /* treat this as though epoll_create1 itself returned EMFILE */ + elog(ERROR, "epoll_create1 failed: %m"); + } + set->epoll_fd = epoll_create1(EPOLL_CLOEXEC); + if (set->epoll_fd < 0) + { + ReleaseExternalFD(); + elog(ERROR, "epoll_create1 failed: %m"); + } +#elif defined(WAIT_USE_KQUEUE) + if (!AcquireExternalFD()) + { + /* treat this as though kqueue itself returned EMFILE */ + elog(ERROR, "kqueue failed: %m"); + } + set->kqueue_fd = kqueue(); + if (set->kqueue_fd < 0) + { + ReleaseExternalFD(); + elog(ERROR, "kqueue failed: %m"); + } + if (fcntl(set->kqueue_fd, F_SETFD, FD_CLOEXEC) == -1) + { + int save_errno = errno; + + close(set->kqueue_fd); + ReleaseExternalFD(); + errno = save_errno; + elog(ERROR, "fcntl(F_SETFD) failed on kqueue descriptor: %m"); + } + set->report_postmaster_not_running = false; +#elif defined(WAIT_USE_WIN32) + + /* + * To handle signals while waiting, we need to add a win32 specific event. + * We accounted for the additional event at the top of this routine. See + * port/win32/signal.c for more details. + * + * 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. + */ + set->handles[0] = pgwin32_signal_event; + StaticAssertStmt(WSA_INVALID_EVENT == NULL, ""); +#endif + + return set; +} + +/* + * Free a previously created WaitEventSet. + * + * Note: preferably, this shouldn't have to free any resources that could be + * inherited across an exec(). If it did, we'd likely leak those resources in + * many scenarios. For the epoll case, we ensure that by setting EPOLL_CLOEXEC + * when the FD is created. For the Windows case, we assume that the handles + * involved are non-inheritable. + */ +void +FreeWaitEventSet(WaitEventSet *set) +{ +#if defined(WAIT_USE_EPOLL) + close(set->epoll_fd); + ReleaseExternalFD(); +#elif defined(WAIT_USE_KQUEUE) + close(set->kqueue_fd); + ReleaseExternalFD(); +#elif defined(WAIT_USE_WIN32) + WaitEvent *cur_event; + + for (cur_event = set->events; + cur_event < (set->events + set->nevents); + cur_event++) + { + if (cur_event->events & WL_LATCH_SET) + { + /* uses the latch's HANDLE */ + } + else if (cur_event->events & WL_POSTMASTER_DEATH) + { + /* uses PostmasterHandle */ + } + else + { + /* Clean up the event object we created for the socket */ + WSAEventSelect(cur_event->fd, NULL, 0); + WSACloseEvent(set->handles[cur_event->pos + 1]); + } + } +#endif + + pfree(set); +} + +/* + * Free a previously created WaitEventSet in a child process after a fork(). + */ +void +FreeWaitEventSetAfterFork(WaitEventSet *set) +{ +#if defined(WAIT_USE_EPOLL) + close(set->epoll_fd); + ReleaseExternalFD(); +#elif defined(WAIT_USE_KQUEUE) + /* kqueues are not normally inherited by child processes */ + ReleaseExternalFD(); +#endif + + pfree(set); +} + +/* --- + * Add an event to the set. Possible events are: + * - WL_LATCH_SET: Wait for the latch to be set + * - WL_POSTMASTER_DEATH: Wait for postmaster to die + * - WL_SOCKET_READABLE: Wait for socket to become readable, + * can be combined in one event with other WL_SOCKET_* events + * - WL_SOCKET_WRITEABLE: Wait for socket to become writeable, + * can be combined with other WL_SOCKET_* events + * - WL_SOCKET_CONNECTED: Wait for socket connection to be established, + * can be combined with other WL_SOCKET_* events (on non-Windows + * platforms, this is the same as WL_SOCKET_WRITEABLE) + * - WL_SOCKET_ACCEPT: Wait for new connection to a server socket, + * can be combined with other WL_SOCKET_* events (on non-Windows + * platforms, this is the same as WL_SOCKET_READABLE) + * - WL_SOCKET_CLOSED: Wait for socket to be closed by remote peer. + * - WL_EXIT_ON_PM_DEATH: Exit immediately if the postmaster dies + * + * Returns the offset in WaitEventSet->events (starting from 0), which can be + * used to modify previously added wait events using ModifyWaitEvent(). + * + * In the WL_LATCH_SET case the latch must be owned by the current process, + * i.e. it must be a process-local latch initialized with InitLatch, or a + * shared latch associated with the current process by calling OwnLatch. + * + * In the WL_SOCKET_READABLE/WRITEABLE/CONNECTED/ACCEPT cases, EOF and error + * conditions cause the socket to be reported as readable/writable/connected, + * so that the caller can deal with the condition. + * + * The user_data pointer specified here will be set for the events returned + * by WaitEventSetWait(), allowing to easily associate additional data with + * events. + */ +int +AddWaitEventToSet(WaitEventSet *set, uint32 events, pgsocket fd, Latch *latch, + void *user_data) +{ + WaitEvent *event; + + /* not enough space */ + Assert(set->nevents < set->nevents_space); + + if (events == WL_EXIT_ON_PM_DEATH) + { + events = WL_POSTMASTER_DEATH; + set->exit_on_postmaster_death = true; + } + + if (latch) + { + if (latch->owner_pid != MyProcPid) + elog(ERROR, "cannot wait on a latch owned by another process"); + if (set->latch) + elog(ERROR, "cannot wait on more than one latch"); + if ((events & WL_LATCH_SET) != WL_LATCH_SET) + elog(ERROR, "latch events only support being set"); + } + else + { + if (events & WL_LATCH_SET) + elog(ERROR, "cannot wait on latch without a specified latch"); + } + + /* waiting for socket readiness without a socket indicates a bug */ + if (fd == PGINVALID_SOCKET && (events & WL_SOCKET_MASK)) + elog(ERROR, "cannot wait on socket event without a socket"); + + event = &set->events[set->nevents]; + event->pos = set->nevents++; + event->fd = fd; + event->events = events; + event->user_data = user_data; +#ifdef WIN32 + event->reset = false; +#endif + + if (events == WL_LATCH_SET) + { + set->latch = latch; + set->latch_pos = event->pos; +#if defined(WAIT_USE_SELF_PIPE) + event->fd = selfpipe_readfd; +#elif defined(WAIT_USE_SIGNALFD) + event->fd = signal_fd; +#else + event->fd = PGINVALID_SOCKET; +#ifdef WAIT_USE_EPOLL + return event->pos; +#endif +#endif + } + else if (events == WL_POSTMASTER_DEATH) + { +#ifndef WIN32 + event->fd = postmaster_alive_fds[POSTMASTER_FD_WATCH]; +#endif + } + + /* perform wait primitive specific initialization, if needed */ +#if defined(WAIT_USE_EPOLL) + WaitEventAdjustEpoll(set, event, EPOLL_CTL_ADD); +#elif defined(WAIT_USE_KQUEUE) + WaitEventAdjustKqueue(set, event, 0); +#elif defined(WAIT_USE_POLL) + WaitEventAdjustPoll(set, event); +#elif defined(WAIT_USE_WIN32) + WaitEventAdjustWin32(set, event); +#endif + + return event->pos; +} + +/* + * Change the event mask and, in the WL_LATCH_SET case, the latch associated + * with the WaitEvent. The latch may be changed to NULL to disable the latch + * temporarily, and then set back to a latch later. + * + * 'pos' is the id returned by AddWaitEventToSet. + */ +void +ModifyWaitEvent(WaitEventSet *set, int pos, uint32 events, Latch *latch) +{ + WaitEvent *event; +#if defined(WAIT_USE_KQUEUE) + int old_events; +#endif + + Assert(pos < set->nevents); + + event = &set->events[pos]; +#if defined(WAIT_USE_KQUEUE) + old_events = event->events; +#endif + + /* + * If neither the event mask nor the associated latch changes, return + * early. That's an important optimization for some sockets, where + * ModifyWaitEvent is frequently used to switch from waiting for reads to + * waiting on writes. + */ + if (events == event->events && + (!(event->events & WL_LATCH_SET) || set->latch == latch)) + return; + + if (event->events & WL_LATCH_SET && + events != event->events) + { + elog(ERROR, "cannot modify latch event"); + } + + if (event->events & WL_POSTMASTER_DEATH) + { + elog(ERROR, "cannot modify postmaster death event"); + } + + /* FIXME: validate event mask */ + event->events = events; + + if (events == WL_LATCH_SET) + { + if (latch && latch->owner_pid != MyProcPid) + elog(ERROR, "cannot wait on a latch owned by another process"); + set->latch = latch; + + /* + * On Unix, we don't need to modify the kernel object because the + * underlying pipe (if there is one) is the same for all latches so we + * can return immediately. On Windows, we need to update our array of + * handles, but we leave the old one in place and tolerate spurious + * wakeups if the latch is disabled. + */ +#if defined(WAIT_USE_WIN32) + if (!latch) + return; +#else + return; +#endif + } + +#if defined(WAIT_USE_EPOLL) + WaitEventAdjustEpoll(set, event, EPOLL_CTL_MOD); +#elif defined(WAIT_USE_KQUEUE) + WaitEventAdjustKqueue(set, event, old_events); +#elif defined(WAIT_USE_POLL) + WaitEventAdjustPoll(set, event); +#elif defined(WAIT_USE_WIN32) + WaitEventAdjustWin32(set, event); +#endif +} + +#if defined(WAIT_USE_EPOLL) +/* + * action can be one of EPOLL_CTL_ADD | EPOLL_CTL_MOD | EPOLL_CTL_DEL + */ +static void +WaitEventAdjustEpoll(WaitEventSet *set, WaitEvent *event, int action) +{ + struct epoll_event epoll_ev; + int rc; + + /* pointer to our event, returned by epoll_wait */ + epoll_ev.data.ptr = event; + /* always wait for errors */ + epoll_ev.events = EPOLLERR | EPOLLHUP; + + /* prepare pollfd entry once */ + if (event->events == WL_LATCH_SET) + { + Assert(set->latch != NULL); + epoll_ev.events |= EPOLLIN; + } + else if (event->events == WL_POSTMASTER_DEATH) + { + epoll_ev.events |= EPOLLIN; + } + else + { + Assert(event->fd != PGINVALID_SOCKET); + Assert(event->events & (WL_SOCKET_READABLE | + WL_SOCKET_WRITEABLE | + WL_SOCKET_CLOSED)); + + if (event->events & WL_SOCKET_READABLE) + epoll_ev.events |= EPOLLIN; + if (event->events & WL_SOCKET_WRITEABLE) + epoll_ev.events |= EPOLLOUT; + if (event->events & WL_SOCKET_CLOSED) + epoll_ev.events |= EPOLLRDHUP; + } + + /* + * Even though unused, we also pass epoll_ev as the data argument if + * EPOLL_CTL_DEL is passed as action. There used to be an epoll bug + * requiring that, and actually it makes the code simpler... + */ + rc = epoll_ctl(set->epoll_fd, action, event->fd, &epoll_ev); + + if (rc < 0) + ereport(ERROR, + (errcode_for_socket_access(), + errmsg("%s() failed: %m", + "epoll_ctl"))); +} +#endif + +#if defined(WAIT_USE_POLL) +static void +WaitEventAdjustPoll(WaitEventSet *set, WaitEvent *event) +{ + struct pollfd *pollfd = &set->pollfds[event->pos]; + + pollfd->revents = 0; + pollfd->fd = event->fd; + + /* prepare pollfd entry once */ + if (event->events == WL_LATCH_SET) + { + Assert(set->latch != NULL); + pollfd->events = POLLIN; + } + else if (event->events == WL_POSTMASTER_DEATH) + { + pollfd->events = POLLIN; + } + else + { + Assert(event->events & (WL_SOCKET_READABLE | + WL_SOCKET_WRITEABLE | + WL_SOCKET_CLOSED)); + pollfd->events = 0; + if (event->events & WL_SOCKET_READABLE) + pollfd->events |= POLLIN; + if (event->events & WL_SOCKET_WRITEABLE) + pollfd->events |= POLLOUT; +#ifdef POLLRDHUP + if (event->events & WL_SOCKET_CLOSED) + pollfd->events |= POLLRDHUP; +#endif + } + + Assert(event->fd != PGINVALID_SOCKET); +} +#endif + +#if defined(WAIT_USE_KQUEUE) + +/* + * On most BSD family systems, the udata member of struct kevent is of type + * void *, so we could directly convert to/from WaitEvent *. Unfortunately, + * NetBSD has it as intptr_t, so here we wallpaper over that difference with + * an lvalue cast. + */ +#define AccessWaitEvent(k_ev) (*((WaitEvent **)(&(k_ev)->udata))) + +static inline void +WaitEventAdjustKqueueAdd(struct kevent *k_ev, int filter, int action, + WaitEvent *event) +{ + k_ev->ident = event->fd; + k_ev->filter = filter; + k_ev->flags = action; + k_ev->fflags = 0; + k_ev->data = 0; + AccessWaitEvent(k_ev) = event; +} + +static inline void +WaitEventAdjustKqueueAddPostmaster(struct kevent *k_ev, WaitEvent *event) +{ + /* For now postmaster death can only be added, not removed. */ + k_ev->ident = PostmasterPid; + k_ev->filter = EVFILT_PROC; + k_ev->flags = EV_ADD; + k_ev->fflags = NOTE_EXIT; + k_ev->data = 0; + AccessWaitEvent(k_ev) = event; +} + +static inline void +WaitEventAdjustKqueueAddLatch(struct kevent *k_ev, WaitEvent *event) +{ + /* For now latch can only be added, not removed. */ + k_ev->ident = SIGURG; + k_ev->filter = EVFILT_SIGNAL; + k_ev->flags = EV_ADD; + k_ev->fflags = 0; + k_ev->data = 0; + AccessWaitEvent(k_ev) = event; +} + +/* + * old_events is the previous event mask, used to compute what has changed. + */ +static void +WaitEventAdjustKqueue(WaitEventSet *set, WaitEvent *event, int old_events) +{ + int rc; + struct kevent k_ev[2]; + int count = 0; + bool new_filt_read = false; + bool old_filt_read = false; + bool new_filt_write = false; + bool old_filt_write = false; + + if (old_events == event->events) + return; + + Assert(event->events != WL_LATCH_SET || set->latch != NULL); + Assert(event->events == WL_LATCH_SET || + event->events == WL_POSTMASTER_DEATH || + (event->events & (WL_SOCKET_READABLE | + WL_SOCKET_WRITEABLE | + WL_SOCKET_CLOSED))); + + if (event->events == WL_POSTMASTER_DEATH) + { + /* + * Unlike all the other implementations, we detect postmaster death + * using process notification instead of waiting on the postmaster + * alive pipe. + */ + WaitEventAdjustKqueueAddPostmaster(&k_ev[count++], event); + } + else if (event->events == WL_LATCH_SET) + { + /* We detect latch wakeup using a signal event. */ + WaitEventAdjustKqueueAddLatch(&k_ev[count++], event); + } + else + { + /* + * We need to compute the adds and deletes required to get from the + * old event mask to the new event mask, since kevent treats readable + * and writable as separate events. + */ + if (old_events & (WL_SOCKET_READABLE | WL_SOCKET_CLOSED)) + old_filt_read = true; + if (event->events & (WL_SOCKET_READABLE | WL_SOCKET_CLOSED)) + new_filt_read = true; + if (old_events & WL_SOCKET_WRITEABLE) + old_filt_write = true; + if (event->events & WL_SOCKET_WRITEABLE) + new_filt_write = true; + if (old_filt_read && !new_filt_read) + WaitEventAdjustKqueueAdd(&k_ev[count++], EVFILT_READ, EV_DELETE, + event); + else if (!old_filt_read && new_filt_read) + WaitEventAdjustKqueueAdd(&k_ev[count++], EVFILT_READ, EV_ADD, + event); + if (old_filt_write && !new_filt_write) + WaitEventAdjustKqueueAdd(&k_ev[count++], EVFILT_WRITE, EV_DELETE, + event); + else if (!old_filt_write && new_filt_write) + WaitEventAdjustKqueueAdd(&k_ev[count++], EVFILT_WRITE, EV_ADD, + event); + } + + /* For WL_SOCKET_READ -> WL_SOCKET_CLOSED, no change needed. */ + if (count == 0) + return; + + Assert(count <= 2); + + rc = kevent(set->kqueue_fd, &k_ev[0], count, NULL, 0, NULL); + + /* + * When adding the postmaster's pid, we have to consider that it might + * already have exited and perhaps even been replaced by another process + * with the same pid. If so, we have to defer reporting this as an event + * until the next call to WaitEventSetWaitBlock(). + */ + + if (rc < 0) + { + if (event->events == WL_POSTMASTER_DEATH && + (errno == ESRCH || errno == EACCES)) + set->report_postmaster_not_running = true; + else + ereport(ERROR, + (errcode_for_socket_access(), + errmsg("%s() failed: %m", + "kevent"))); + } + else if (event->events == WL_POSTMASTER_DEATH && + PostmasterPid != getppid() && + !PostmasterIsAlive()) + { + /* + * The extra PostmasterIsAliveInternal() check prevents false alarms + * on systems that give a different value for getppid() while being + * traced by a debugger. + */ + set->report_postmaster_not_running = true; + } +} + +#endif + +#if defined(WAIT_USE_WIN32) +static void +WaitEventAdjustWin32(WaitEventSet *set, WaitEvent *event) +{ + HANDLE *handle = &set->handles[event->pos + 1]; + + if (event->events == WL_LATCH_SET) + { + Assert(set->latch != NULL); + *handle = set->latch->event; + } + else if (event->events == WL_POSTMASTER_DEATH) + { + *handle = PostmasterHandle; + } + else + { + int flags = FD_CLOSE; /* always check for errors/EOF */ + + if (event->events & WL_SOCKET_READABLE) + flags |= FD_READ; + if (event->events & WL_SOCKET_WRITEABLE) + flags |= FD_WRITE; + if (event->events & WL_SOCKET_CONNECTED) + flags |= FD_CONNECT; + if (event->events & WL_SOCKET_ACCEPT) + flags |= FD_ACCEPT; + + if (*handle == WSA_INVALID_EVENT) + { + *handle = WSACreateEvent(); + if (*handle == WSA_INVALID_EVENT) + elog(ERROR, "failed to create event for socket: error code %d", + WSAGetLastError()); + } + if (WSAEventSelect(event->fd, *handle, flags) != 0) + elog(ERROR, "failed to set up event for socket: error code %d", + WSAGetLastError()); + + Assert(event->fd != PGINVALID_SOCKET); + } +} +#endif + +/* + * Wait for events added to the set to happen, or until the timeout is + * reached. At most nevents occurred events are returned. + * + * If timeout = -1, block until an event occurs; if 0, check sockets for + * readiness, but don't block; if > 0, block for at most timeout milliseconds. + * + * Returns the number of events occurred, or 0 if the timeout was reached. + * + * Returned events will have the fd, pos, user_data fields set to the + * values associated with the registered event. + */ +int +WaitEventSetWait(WaitEventSet *set, long timeout, + WaitEvent *occurred_events, int nevents, + uint32 wait_event_info) +{ + int returned_events = 0; + instr_time start_time; + instr_time cur_time; + long cur_timeout = -1; + + Assert(nevents > 0); + + /* + * Initialize timeout if requested. We must record the current time so + * that we can determine the remaining timeout if interrupted. + */ + if (timeout >= 0) + { + INSTR_TIME_SET_CURRENT(start_time); + Assert(timeout >= 0 && timeout <= INT_MAX); + cur_timeout = timeout; + } + else + INSTR_TIME_SET_ZERO(start_time); + + pgstat_report_wait_start(wait_event_info); + +#ifndef WIN32 + waiting = true; +#else + /* Ensure that signals are serviced even if latch is already set */ + pgwin32_dispatch_queued_signals(); +#endif + while (returned_events == 0) + { + int rc; + + /* + * Check if the latch is set already. If so, leave the loop + * immediately, avoid blocking again. We don't attempt to report any + * other events that might also be satisfied. + * + * If someone sets the latch between this and the + * WaitEventSetWaitBlock() below, the setter will write a byte to the + * pipe (or signal us and the signal handler will do that), and the + * readiness routine will return immediately. + * + * On unix, If there's a pending byte in the self pipe, we'll notice + * whenever blocking. Only clearing the pipe in that case avoids + * having to drain it every time WaitLatchOrSocket() is used. Should + * the pipe-buffer fill up we're still ok, because the pipe is in + * nonblocking mode. It's unlikely for that to happen, because the + * self pipe isn't filled unless we're blocking (waiting = true), or + * from inside a signal handler in latch_sigurg_handler(). + * + * On windows, we'll also notice if there's a pending event for the + * latch when blocking, but there's no danger of anything filling up, + * as "Setting an event that is already set has no effect.". + * + * Note: we assume that the kernel calls involved in latch management + * will provide adequate synchronization on machines with weak memory + * ordering, so that we cannot miss seeing is_set if a notification + * has already been queued. + */ + if (set->latch && !set->latch->is_set) + { + /* about to sleep on a latch */ + set->latch->maybe_sleeping = true; + pg_memory_barrier(); + /* and recheck */ + } + + if (set->latch && set->latch->is_set) + { + occurred_events->fd = PGINVALID_SOCKET; + occurred_events->pos = set->latch_pos; + occurred_events->user_data = + set->events[set->latch_pos].user_data; + occurred_events->events = WL_LATCH_SET; + occurred_events++; + returned_events++; + + /* could have been set above */ + set->latch->maybe_sleeping = false; + + break; + } + + /* + * Wait for events using the readiness primitive chosen at the top of + * this file. If -1 is returned, a timeout has occurred, if 0 we have + * to retry, everything >= 1 is the number of returned events. + */ + rc = WaitEventSetWaitBlock(set, cur_timeout, + occurred_events, nevents); + + if (set->latch) + { + Assert(set->latch->maybe_sleeping); + set->latch->maybe_sleeping = false; + } + + if (rc == -1) + break; /* timeout occurred */ + else + returned_events = rc; + + /* If we're not done, update cur_timeout for next iteration */ + if (returned_events == 0 && timeout >= 0) + { + INSTR_TIME_SET_CURRENT(cur_time); + INSTR_TIME_SUBTRACT(cur_time, start_time); + cur_timeout = timeout - (long) INSTR_TIME_GET_MILLISEC(cur_time); + if (cur_timeout <= 0) + break; + } + } +#ifndef WIN32 + waiting = false; +#endif + + pgstat_report_wait_end(); + + return returned_events; +} + + +#if defined(WAIT_USE_EPOLL) + +/* + * Wait using linux's epoll_wait(2). + * + * This is the preferable wait method, as several readiness notifications are + * delivered, without having to iterate through all of set->events. The return + * epoll_event struct contain a pointer to our events, making association + * easy. + */ +static inline int +WaitEventSetWaitBlock(WaitEventSet *set, int cur_timeout, + WaitEvent *occurred_events, int nevents) +{ + int returned_events = 0; + int rc; + WaitEvent *cur_event; + struct epoll_event *cur_epoll_event; + + /* Sleep */ + rc = epoll_wait(set->epoll_fd, set->epoll_ret_events, + Min(nevents, set->nevents_space), cur_timeout); + + /* Check return code */ + if (rc < 0) + { + /* EINTR is okay, otherwise complain */ + if (errno != EINTR) + { + waiting = false; + ereport(ERROR, + (errcode_for_socket_access(), + errmsg("%s() failed: %m", + "epoll_wait"))); + } + return 0; + } + else if (rc == 0) + { + /* timeout exceeded */ + return -1; + } + + /* + * At least one event occurred, iterate over the returned epoll events + * until they're either all processed, or we've returned all the events + * the caller desired. + */ + for (cur_epoll_event = set->epoll_ret_events; + cur_epoll_event < (set->epoll_ret_events + rc) && + returned_events < nevents; + cur_epoll_event++) + { + /* epoll's data pointer is set to the associated WaitEvent */ + cur_event = (WaitEvent *) cur_epoll_event->data.ptr; + + occurred_events->pos = cur_event->pos; + occurred_events->user_data = cur_event->user_data; + occurred_events->events = 0; + + if (cur_event->events == WL_LATCH_SET && + cur_epoll_event->events & (EPOLLIN | EPOLLERR | EPOLLHUP)) + { + /* Drain the signalfd. */ + drain(); + + if (set->latch && set->latch->is_set) + { + occurred_events->fd = PGINVALID_SOCKET; + occurred_events->events = WL_LATCH_SET; + occurred_events++; + returned_events++; + } + } + else if (cur_event->events == WL_POSTMASTER_DEATH && + cur_epoll_event->events & (EPOLLIN | EPOLLERR | EPOLLHUP)) + { + /* + * We expect an EPOLLHUP when the remote end is closed, but + * because we don't expect the pipe to become readable or to have + * any errors either, treat those cases as postmaster death, too. + * + * Be paranoid about a spurious event signaling the postmaster as + * being dead. There have been reports about that happening with + * older primitives (select(2) to be specific), and a spurious + * WL_POSTMASTER_DEATH event would be painful. Re-checking doesn't + * cost much. + */ + if (!PostmasterIsAliveInternal()) + { + if (set->exit_on_postmaster_death) + proc_exit(1); + occurred_events->fd = PGINVALID_SOCKET; + occurred_events->events = WL_POSTMASTER_DEATH; + occurred_events++; + returned_events++; + } + } + else if (cur_event->events & (WL_SOCKET_READABLE | + WL_SOCKET_WRITEABLE | + WL_SOCKET_CLOSED)) + { + Assert(cur_event->fd != PGINVALID_SOCKET); + + if ((cur_event->events & WL_SOCKET_READABLE) && + (cur_epoll_event->events & (EPOLLIN | EPOLLERR | EPOLLHUP))) + { + /* data available in socket, or EOF */ + occurred_events->events |= WL_SOCKET_READABLE; + } + + if ((cur_event->events & WL_SOCKET_WRITEABLE) && + (cur_epoll_event->events & (EPOLLOUT | EPOLLERR | EPOLLHUP))) + { + /* writable, or EOF */ + occurred_events->events |= WL_SOCKET_WRITEABLE; + } + + if ((cur_event->events & WL_SOCKET_CLOSED) && + (cur_epoll_event->events & (EPOLLRDHUP | EPOLLERR | EPOLLHUP))) + { + /* remote peer shut down, or error */ + occurred_events->events |= WL_SOCKET_CLOSED; + } + + if (occurred_events->events != 0) + { + occurred_events->fd = cur_event->fd; + occurred_events++; + returned_events++; + } + } + } + + return returned_events; +} + +#elif defined(WAIT_USE_KQUEUE) + +/* + * Wait using kevent(2) on BSD-family systems and macOS. + * + * For now this mirrors the epoll code, but in future it could modify the fd + * set in the same call to kevent as it uses for waiting instead of doing that + * with separate system calls. + */ +static int +WaitEventSetWaitBlock(WaitEventSet *set, int cur_timeout, + WaitEvent *occurred_events, int nevents) +{ + int returned_events = 0; + int rc; + WaitEvent *cur_event; + struct kevent *cur_kqueue_event; + struct timespec timeout; + struct timespec *timeout_p; + + if (cur_timeout < 0) + timeout_p = NULL; + else + { + timeout.tv_sec = cur_timeout / 1000; + timeout.tv_nsec = (cur_timeout % 1000) * 1000000; + timeout_p = &timeout; + } + + /* + * Report postmaster events discovered by WaitEventAdjustKqueue() or an + * earlier call to WaitEventSetWait(). + */ + if (unlikely(set->report_postmaster_not_running)) + { + if (set->exit_on_postmaster_death) + proc_exit(1); + occurred_events->fd = PGINVALID_SOCKET; + occurred_events->events = WL_POSTMASTER_DEATH; + return 1; + } + + /* Sleep */ + rc = kevent(set->kqueue_fd, NULL, 0, + set->kqueue_ret_events, + Min(nevents, set->nevents_space), + timeout_p); + + /* Check return code */ + if (rc < 0) + { + /* EINTR is okay, otherwise complain */ + if (errno != EINTR) + { + waiting = false; + ereport(ERROR, + (errcode_for_socket_access(), + errmsg("%s() failed: %m", + "kevent"))); + } + return 0; + } + else if (rc == 0) + { + /* timeout exceeded */ + return -1; + } + + /* + * At least one event occurred, iterate over the returned kqueue events + * until they're either all processed, or we've returned all the events + * the caller desired. + */ + for (cur_kqueue_event = set->kqueue_ret_events; + cur_kqueue_event < (set->kqueue_ret_events + rc) && + returned_events < nevents; + cur_kqueue_event++) + { + /* kevent's udata points to the associated WaitEvent */ + cur_event = AccessWaitEvent(cur_kqueue_event); + + occurred_events->pos = cur_event->pos; + occurred_events->user_data = cur_event->user_data; + occurred_events->events = 0; + + if (cur_event->events == WL_LATCH_SET && + cur_kqueue_event->filter == EVFILT_SIGNAL) + { + if (set->latch && set->latch->is_set) + { + occurred_events->fd = PGINVALID_SOCKET; + occurred_events->events = WL_LATCH_SET; + occurred_events++; + returned_events++; + } + } + else if (cur_event->events == WL_POSTMASTER_DEATH && + cur_kqueue_event->filter == EVFILT_PROC && + (cur_kqueue_event->fflags & NOTE_EXIT) != 0) + { + /* + * The kernel will tell this kqueue object only once about the + * exit of the postmaster, so let's remember that for next time so + * that we provide level-triggered semantics. + */ + set->report_postmaster_not_running = true; + + if (set->exit_on_postmaster_death) + proc_exit(1); + occurred_events->fd = PGINVALID_SOCKET; + occurred_events->events = WL_POSTMASTER_DEATH; + occurred_events++; + returned_events++; + } + else if (cur_event->events & (WL_SOCKET_READABLE | + WL_SOCKET_WRITEABLE | + WL_SOCKET_CLOSED)) + { + Assert(cur_event->fd >= 0); + + if ((cur_event->events & WL_SOCKET_READABLE) && + (cur_kqueue_event->filter == EVFILT_READ)) + { + /* readable, or EOF */ + occurred_events->events |= WL_SOCKET_READABLE; + } + + if ((cur_event->events & WL_SOCKET_CLOSED) && + (cur_kqueue_event->filter == EVFILT_READ) && + (cur_kqueue_event->flags & EV_EOF)) + { + /* the remote peer has shut down */ + occurred_events->events |= WL_SOCKET_CLOSED; + } + + if ((cur_event->events & WL_SOCKET_WRITEABLE) && + (cur_kqueue_event->filter == EVFILT_WRITE)) + { + /* writable, or EOF */ + occurred_events->events |= WL_SOCKET_WRITEABLE; + } + + if (occurred_events->events != 0) + { + occurred_events->fd = cur_event->fd; + occurred_events++; + returned_events++; + } + } + } + + return returned_events; +} + +#elif defined(WAIT_USE_POLL) + +/* + * Wait using poll(2). + * + * This allows to receive readiness notifications for several events at once, + * but requires iterating through all of set->pollfds. + */ +static inline int +WaitEventSetWaitBlock(WaitEventSet *set, int cur_timeout, + WaitEvent *occurred_events, int nevents) +{ + int returned_events = 0; + int rc; + WaitEvent *cur_event; + struct pollfd *cur_pollfd; + + /* Sleep */ + rc = poll(set->pollfds, set->nevents, (int) cur_timeout); + + /* Check return code */ + if (rc < 0) + { + /* EINTR is okay, otherwise complain */ + if (errno != EINTR) + { + waiting = false; + ereport(ERROR, + (errcode_for_socket_access(), + errmsg("%s() failed: %m", + "poll"))); + } + return 0; + } + else if (rc == 0) + { + /* timeout exceeded */ + return -1; + } + + for (cur_event = set->events, cur_pollfd = set->pollfds; + cur_event < (set->events + set->nevents) && + returned_events < nevents; + cur_event++, cur_pollfd++) + { + /* no activity on this FD, skip */ + if (cur_pollfd->revents == 0) + continue; + + occurred_events->pos = cur_event->pos; + occurred_events->user_data = cur_event->user_data; + occurred_events->events = 0; + + if (cur_event->events == WL_LATCH_SET && + (cur_pollfd->revents & (POLLIN | POLLHUP | POLLERR | POLLNVAL))) + { + /* There's data in the self-pipe, clear it. */ + drain(); + + if (set->latch && set->latch->is_set) + { + occurred_events->fd = PGINVALID_SOCKET; + occurred_events->events = WL_LATCH_SET; + occurred_events++; + returned_events++; + } + } + else if (cur_event->events == WL_POSTMASTER_DEATH && + (cur_pollfd->revents & (POLLIN | POLLHUP | POLLERR | POLLNVAL))) + { + /* + * We expect an POLLHUP when the remote end is closed, but because + * we don't expect the pipe to become readable or to have any + * errors either, treat those cases as postmaster death, too. + * + * Be paranoid about a spurious event signaling the postmaster as + * being dead. There have been reports about that happening with + * older primitives (select(2) to be specific), and a spurious + * WL_POSTMASTER_DEATH event would be painful. Re-checking doesn't + * cost much. + */ + if (!PostmasterIsAliveInternal()) + { + if (set->exit_on_postmaster_death) + proc_exit(1); + occurred_events->fd = PGINVALID_SOCKET; + occurred_events->events = WL_POSTMASTER_DEATH; + occurred_events++; + returned_events++; + } + } + else if (cur_event->events & (WL_SOCKET_READABLE | + WL_SOCKET_WRITEABLE | + WL_SOCKET_CLOSED)) + { + int errflags = POLLHUP | POLLERR | POLLNVAL; + + Assert(cur_event->fd >= PGINVALID_SOCKET); + + if ((cur_event->events & WL_SOCKET_READABLE) && + (cur_pollfd->revents & (POLLIN | errflags))) + { + /* data available in socket, or EOF */ + occurred_events->events |= WL_SOCKET_READABLE; + } + + if ((cur_event->events & WL_SOCKET_WRITEABLE) && + (cur_pollfd->revents & (POLLOUT | errflags))) + { + /* writeable, or EOF */ + occurred_events->events |= WL_SOCKET_WRITEABLE; + } + +#ifdef POLLRDHUP + if ((cur_event->events & WL_SOCKET_CLOSED) && + (cur_pollfd->revents & (POLLRDHUP | errflags))) + { + /* remote peer closed, or error */ + occurred_events->events |= WL_SOCKET_CLOSED; + } +#endif + + if (occurred_events->events != 0) + { + occurred_events->fd = cur_event->fd; + occurred_events++; + returned_events++; + } + } + } + return returned_events; +} + +#elif defined(WAIT_USE_WIN32) + +/* + * Wait using Windows' WaitForMultipleObjects(). + * + * Unfortunately this will only ever return a single readiness notification at + * a time. Note that while the official documentation for + * WaitForMultipleObjects is ambiguous about multiple events being "consumed" + * with a single bWaitAll = FALSE call, + * https://blogs.msdn.microsoft.com/oldnewthing/20150409-00/?p=44273 confirms + * that only one event is "consumed". + */ +static inline int +WaitEventSetWaitBlock(WaitEventSet *set, int cur_timeout, + WaitEvent *occurred_events, int nevents) +{ + int returned_events = 0; + DWORD rc; + WaitEvent *cur_event; + + /* Reset any wait events that need it */ + for (cur_event = set->events; + cur_event < (set->events + set->nevents); + cur_event++) + { + if (cur_event->reset) + { + WaitEventAdjustWin32(set, cur_event); + cur_event->reset = false; + } + + /* + * 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 (cur_event->events & WL_SOCKET_WRITEABLE) + { + char c; + WSABUF buf; + DWORD sent; + int r; + + buf.buf = &c; + buf.len = 0; + + r = WSASend(cur_event->fd, &buf, 1, &sent, 0, NULL, NULL); + if (r == 0 || WSAGetLastError() != WSAEWOULDBLOCK) + { + occurred_events->pos = cur_event->pos; + occurred_events->user_data = cur_event->user_data; + occurred_events->events = WL_SOCKET_WRITEABLE; + occurred_events->fd = cur_event->fd; + return 1; + } + } + } + + /* + * Sleep. + * + * Need to wait for ->nevents + 1, because signal handle is in [0]. + */ + rc = WaitForMultipleObjects(set->nevents + 1, set->handles, FALSE, + cur_timeout); + + /* Check return code */ + if (rc == WAIT_FAILED) + elog(ERROR, "WaitForMultipleObjects() failed: error code %lu", + GetLastError()); + else if (rc == WAIT_TIMEOUT) + { + /* timeout exceeded */ + return -1; + } + + if (rc == WAIT_OBJECT_0) + { + /* Service newly-arrived signals */ + pgwin32_dispatch_queued_signals(); + return 0; /* retry */ + } + + /* + * With an offset of one, due to the always present pgwin32_signal_event, + * the handle offset directly corresponds to a wait event. + */ + cur_event = (WaitEvent *) &set->events[rc - WAIT_OBJECT_0 - 1]; + + occurred_events->pos = cur_event->pos; + occurred_events->user_data = cur_event->user_data; + occurred_events->events = 0; + + if (cur_event->events == WL_LATCH_SET) + { + /* + * We cannot use set->latch->event to reset the fired event if we + * aren't waiting on this latch now. + */ + if (!ResetEvent(set->handles[cur_event->pos + 1])) + elog(ERROR, "ResetEvent failed: error code %lu", GetLastError()); + + if (set->latch && set->latch->is_set) + { + occurred_events->fd = PGINVALID_SOCKET; + occurred_events->events = WL_LATCH_SET; + occurred_events++; + returned_events++; + } + } + else if (cur_event->events == WL_POSTMASTER_DEATH) + { + /* + * Postmaster apparently died. Since the consequences of falsely + * returning WL_POSTMASTER_DEATH could be pretty unpleasant, we take + * the trouble to positively verify this with PostmasterIsAlive(), + * even though there is no known reason to think that the event could + * be falsely set on Windows. + */ + if (!PostmasterIsAliveInternal()) + { + if (set->exit_on_postmaster_death) + proc_exit(1); + occurred_events->fd = PGINVALID_SOCKET; + occurred_events->events = WL_POSTMASTER_DEATH; + occurred_events++; + returned_events++; + } + } + else if (cur_event->events & WL_SOCKET_MASK) + { + WSANETWORKEVENTS resEvents; + HANDLE handle = set->handles[cur_event->pos + 1]; + + Assert(cur_event->fd); + + occurred_events->fd = cur_event->fd; + + ZeroMemory(&resEvents, sizeof(resEvents)); + if (WSAEnumNetworkEvents(cur_event->fd, handle, &resEvents) != 0) + elog(ERROR, "failed to enumerate network events: error code %d", + WSAGetLastError()); + if ((cur_event->events & WL_SOCKET_READABLE) && + (resEvents.lNetworkEvents & FD_READ)) + { + /* data available in socket */ + occurred_events->events |= WL_SOCKET_READABLE; + + /*------ + * WaitForMultipleObjects doesn't guarantee that a read event will + * be returned if the latch is set at the same time. Even if it + * did, the caller might drop that event expecting it to reoccur + * on next call. So, we must force the event to be reset if this + * WaitEventSet is used again in order to avoid an indefinite + * hang. Refer https://msdn.microsoft.com/en-us/library/windows/desktop/ms741576(v=vs.85).aspx + * for the behavior of socket events. + *------ + */ + cur_event->reset = true; + } + if ((cur_event->events & WL_SOCKET_WRITEABLE) && + (resEvents.lNetworkEvents & FD_WRITE)) + { + /* writeable */ + occurred_events->events |= WL_SOCKET_WRITEABLE; + } + if ((cur_event->events & WL_SOCKET_CONNECTED) && + (resEvents.lNetworkEvents & FD_CONNECT)) + { + /* connected */ + occurred_events->events |= WL_SOCKET_CONNECTED; + } + if ((cur_event->events & WL_SOCKET_ACCEPT) && + (resEvents.lNetworkEvents & FD_ACCEPT)) + { + /* incoming connection could be accepted */ + occurred_events->events |= WL_SOCKET_ACCEPT; + } + if (resEvents.lNetworkEvents & FD_CLOSE) + { + /* EOF/error, so signal all caller-requested socket flags */ + occurred_events->events |= (cur_event->events & WL_SOCKET_MASK); + } + + if (occurred_events->events != 0) + { + occurred_events++; + returned_events++; + } + } + + return returned_events; +} +#endif + +/* + * Return whether the current build options can report WL_SOCKET_CLOSED. + */ +bool +WaitEventSetCanReportClosed(void) +{ +#if (defined(WAIT_USE_POLL) && defined(POLLRDHUP)) || \ + defined(WAIT_USE_EPOLL) || \ + defined(WAIT_USE_KQUEUE) + return true; +#else + return false; +#endif +} + +/* + * Get the number of wait events registered in a given WaitEventSet. + */ +int +GetNumRegisteredWaitEvents(WaitEventSet *set) +{ + return set->nevents; +} + +#if defined(WAIT_USE_SELF_PIPE) + +/* + * SetLatch uses SIGURG to wake up the process waiting on the latch. + * + * Wake up WaitLatch, if we're waiting. + */ +static void +latch_sigurg_handler(SIGNAL_ARGS) +{ + int save_errno = errno; + + if (waiting) + sendSelfPipeByte(); + + errno = save_errno; +} + +/* Send one byte to the self-pipe, to wake up WaitLatch */ +static void +sendSelfPipeByte(void) +{ + int rc; + char dummy = 0; + +retry: + rc = write(selfpipe_writefd, &dummy, 1); + if (rc < 0) + { + /* If interrupted by signal, just retry */ + if (errno == EINTR) + goto retry; + + /* + * If the pipe is full, we don't need to retry, the data that's there + * already is enough to wake up WaitLatch. + */ + if (errno == EAGAIN || errno == EWOULDBLOCK) + return; + + /* + * Oops, the write() failed for some other reason. We might be in a + * signal handler, so it's not safe to elog(). We have no choice but + * silently ignore the error. + */ + return; + } +} + +#endif + +#if defined(WAIT_USE_SELF_PIPE) || defined(WAIT_USE_SIGNALFD) + +/* + * Read all available data from self-pipe or signalfd. + * + * Note: this is only called when waiting = true. If it fails and doesn't + * return, it must reset that flag first (though ideally, this will never + * happen). + */ +static void +drain(void) +{ + char buf[1024]; + int rc; + int fd; + +#ifdef WAIT_USE_SELF_PIPE + fd = selfpipe_readfd; +#else + fd = signal_fd; +#endif + + for (;;) + { + rc = read(fd, buf, sizeof(buf)); + if (rc < 0) + { + if (errno == EAGAIN || errno == EWOULDBLOCK) + break; /* the descriptor is empty */ + else if (errno == EINTR) + continue; /* retry */ + else + { + waiting = false; +#ifdef WAIT_USE_SELF_PIPE + elog(ERROR, "read() on self-pipe failed: %m"); +#else + elog(ERROR, "read() on signalfd failed: %m"); +#endif + } + } + else if (rc == 0) + { + waiting = false; +#ifdef WAIT_USE_SELF_PIPE + elog(ERROR, "unexpected EOF on self-pipe"); +#else + elog(ERROR, "unexpected EOF on signalfd"); +#endif + } + else if (rc < sizeof(buf)) + { + /* we successfully drained the pipe; no need to read() again */ + break; + } + /* else buffer wasn't big enough, so read again */ + } +} + +#endif |