1 files changed, 318 insertions, 0 deletions

diff --git a/src/backend/libpq/pqmq.c b/src/backend/libpq/pqmq.c
new file mode 100644
index 0000000..4d0415e
--- /dev/null
+++ b/src/backend/libpq/pqmq.c
@@ -0,0 +1,318 @@
+/*-------------------------------------------------------------------------
+ *
+ * pqmq.c
+ *	  Use the frontend/backend protocol for communication over a shm_mq
+ *
+ * Portions Copyright (c) 1996-2022, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ *	src/backend/libpq/pqmq.c
+ *
+ *-------------------------------------------------------------------------
+ */
+
+#include "postgres.h"
+
+#include "libpq/libpq.h"
+#include "libpq/pqformat.h"
+#include "libpq/pqmq.h"
+#include "miscadmin.h"
+#include "pgstat.h"
+#include "tcop/tcopprot.h"
+#include "utils/builtins.h"
+
+static shm_mq_handle *pq_mq_handle;
+static bool pq_mq_busy = false;
+static pid_t pq_mq_parallel_leader_pid = 0;
+static pid_t pq_mq_parallel_leader_backend_id = InvalidBackendId;
+
+static void pq_cleanup_redirect_to_shm_mq(dsm_segment *seg, Datum arg);
+static void mq_comm_reset(void);
+static int	mq_flush(void);
+static int	mq_flush_if_writable(void);
+static bool mq_is_send_pending(void);
+static int	mq_putmessage(char msgtype, const char *s, size_t len);
+static void mq_putmessage_noblock(char msgtype, const char *s, size_t len);
+
+static const PQcommMethods PqCommMqMethods = {
+	mq_comm_reset,
+	mq_flush,
+	mq_flush_if_writable,
+	mq_is_send_pending,
+	mq_putmessage,
+	mq_putmessage_noblock
+};
+
+/*
+ * Arrange to redirect frontend/backend protocol messages to a shared-memory
+ * message queue.
+ */
+void
+pq_redirect_to_shm_mq(dsm_segment *seg, shm_mq_handle *mqh)
+{
+	PqCommMethods = &PqCommMqMethods;
+	pq_mq_handle = mqh;
+	whereToSendOutput = DestRemote;
+	FrontendProtocol = PG_PROTOCOL_LATEST;
+	on_dsm_detach(seg, pq_cleanup_redirect_to_shm_mq, (Datum) 0);
+}
+
+/*
+ * When the DSM that contains our shm_mq goes away, we need to stop sending
+ * messages to it.
+ */
+static void
+pq_cleanup_redirect_to_shm_mq(dsm_segment *seg, Datum arg)
+{
+	pq_mq_handle = NULL;
+	whereToSendOutput = DestNone;
+}
+
+/*
+ * Arrange to SendProcSignal() to the parallel leader each time we transmit
+ * message data via the shm_mq.
+ */
+void
+pq_set_parallel_leader(pid_t pid, BackendId backend_id)
+{
+	Assert(PqCommMethods == &PqCommMqMethods);
+	pq_mq_parallel_leader_pid = pid;
+	pq_mq_parallel_leader_backend_id = backend_id;
+}
+
+static void
+mq_comm_reset(void)
+{
+	/* Nothing to do. */
+}
+
+static int
+mq_flush(void)
+{
+	/* Nothing to do. */
+	return 0;
+}
+
+static int
+mq_flush_if_writable(void)
+{
+	/* Nothing to do. */
+	return 0;
+}
+
+static bool
+mq_is_send_pending(void)
+{
+	/* There's never anything pending. */
+	return 0;
+}
+
+/*
+ * Transmit a libpq protocol message to the shared memory message queue
+ * selected via pq_mq_handle.  We don't include a length word, because the
+ * receiver will know the length of the message from shm_mq_receive().
+ */
+static int
+mq_putmessage(char msgtype, const char *s, size_t len)
+{
+	shm_mq_iovec iov[2];
+	shm_mq_result result;
+
+	/*
+	 * If we're sending a message, and we have to wait because the queue is
+	 * full, and then we get interrupted, and that interrupt results in trying
+	 * to send another message, we respond by detaching the queue.  There's no
+	 * way to return to the original context, but even if there were, just
+	 * queueing the message would amount to indefinitely postponing the
+	 * response to the interrupt.  So we do this instead.
+	 */
+	if (pq_mq_busy)
+	{
+		if (pq_mq_handle != NULL)
+			shm_mq_detach(pq_mq_handle);
+		pq_mq_handle = NULL;
+		return EOF;
+	}
+
+	/*
+	 * If the message queue is already gone, just ignore the message. This
+	 * doesn't necessarily indicate a problem; for example, DEBUG messages can
+	 * be generated late in the shutdown sequence, after all DSMs have already
+	 * been detached.
+	 */
+	if (pq_mq_handle == NULL)
+		return 0;
+
+	pq_mq_busy = true;
+
+	iov[0].data = &msgtype;
+	iov[0].len = 1;
+	iov[1].data = s;
+	iov[1].len = len;
+
+	Assert(pq_mq_handle != NULL);
+
+	for (;;)
+	{
+		/*
+		 * Immediately notify the receiver by passing force_flush as true so
+		 * that the shared memory value is updated before we send the parallel
+		 * message signal right after this.
+		 */
+		result = shm_mq_sendv(pq_mq_handle, iov, 2, true, true);
+
+		if (pq_mq_parallel_leader_pid != 0)
+			SendProcSignal(pq_mq_parallel_leader_pid,
+						   PROCSIG_PARALLEL_MESSAGE,
+						   pq_mq_parallel_leader_backend_id);
+
+		if (result != SHM_MQ_WOULD_BLOCK)
+			break;
+
+		(void) WaitLatch(MyLatch, WL_LATCH_SET | WL_EXIT_ON_PM_DEATH, 0,
+						 WAIT_EVENT_MQ_PUT_MESSAGE);
+		ResetLatch(MyLatch);
+		CHECK_FOR_INTERRUPTS();
+	}
+
+	pq_mq_busy = false;
+
+	Assert(result == SHM_MQ_SUCCESS || result == SHM_MQ_DETACHED);
+	if (result != SHM_MQ_SUCCESS)
+		return EOF;
+	return 0;
+}
+
+static void
+mq_putmessage_noblock(char msgtype, const char *s, size_t len)
+{
+	/*
+	 * While the shm_mq machinery does support sending a message in
+	 * non-blocking mode, there's currently no way to try sending beginning to
+	 * send the message that doesn't also commit us to completing the
+	 * transmission.  This could be improved in the future, but for now we
+	 * don't need it.
+	 */
+	elog(ERROR, "not currently supported");
+}
+
+/*
+ * Parse an ErrorResponse or NoticeResponse payload and populate an ErrorData
+ * structure with the results.
+ */
+void
+pq_parse_errornotice(StringInfo msg, ErrorData *edata)
+{
+	/* Initialize edata with reasonable defaults. */
+	MemSet(edata, 0, sizeof(ErrorData));
+	edata->elevel = ERROR;
+	edata->assoc_context = CurrentMemoryContext;
+
+	/* Loop over fields and extract each one. */
+	for (;;)
+	{
+		char		code = pq_getmsgbyte(msg);
+		const char *value;
+
+		if (code == '\0')
+		{
+			pq_getmsgend(msg);
+			break;
+		}
+		value = pq_getmsgrawstring(msg);
+
+		switch (code)
+		{
+			case PG_DIAG_SEVERITY:
+				/* ignore, trusting we'll get a nonlocalized version */
+				break;
+			case PG_DIAG_SEVERITY_NONLOCALIZED:
+				if (strcmp(value, "DEBUG") == 0)
+				{
+					/*
+					 * We can't reconstruct the exact DEBUG level, but
+					 * presumably it was >= client_min_messages, so select
+					 * DEBUG1 to ensure we'll pass it on to the client.
+					 */
+					edata->elevel = DEBUG1;
+				}
+				else if (strcmp(value, "LOG") == 0)
+				{
+					/*
+					 * It can't be LOG_SERVER_ONLY, or the worker wouldn't
+					 * have sent it to us; so LOG is the correct value.
+					 */
+					edata->elevel = LOG;
+				}
+				else if (strcmp(value, "INFO") == 0)
+					edata->elevel = INFO;
+				else if (strcmp(value, "NOTICE") == 0)
+					edata->elevel = NOTICE;
+				else if (strcmp(value, "WARNING") == 0)
+					edata->elevel = WARNING;
+				else if (strcmp(value, "ERROR") == 0)
+					edata->elevel = ERROR;
+				else if (strcmp(value, "FATAL") == 0)
+					edata->elevel = FATAL;
+				else if (strcmp(value, "PANIC") == 0)
+					edata->elevel = PANIC;
+				else
+					elog(ERROR, "unrecognized error severity: \"%s\"", value);
+				break;
+			case PG_DIAG_SQLSTATE:
+				if (strlen(value) != 5)
+					elog(ERROR, "invalid SQLSTATE: \"%s\"", value);
+				edata->sqlerrcode = MAKE_SQLSTATE(value[0], value[1], value[2],
+												  value[3], value[4]);
+				break;
+			case PG_DIAG_MESSAGE_PRIMARY:
+				edata->message = pstrdup(value);
+				break;
+			case PG_DIAG_MESSAGE_DETAIL:
+				edata->detail = pstrdup(value);
+				break;
+			case PG_DIAG_MESSAGE_HINT:
+				edata->hint = pstrdup(value);
+				break;
+			case PG_DIAG_STATEMENT_POSITION:
+				edata->cursorpos = pg_strtoint32(value);
+				break;
+			case PG_DIAG_INTERNAL_POSITION:
+				edata->internalpos = pg_strtoint32(value);
+				break;
+			case PG_DIAG_INTERNAL_QUERY:
+				edata->internalquery = pstrdup(value);
+				break;
+			case PG_DIAG_CONTEXT:
+				edata->context = pstrdup(value);
+				break;
+			case PG_DIAG_SCHEMA_NAME:
+				edata->schema_name = pstrdup(value);
+				break;
+			case PG_DIAG_TABLE_NAME:
+				edata->table_name = pstrdup(value);
+				break;
+			case PG_DIAG_COLUMN_NAME:
+				edata->column_name = pstrdup(value);
+				break;
+			case PG_DIAG_DATATYPE_NAME:
+				edata->datatype_name = pstrdup(value);
+				break;
+			case PG_DIAG_CONSTRAINT_NAME:
+				edata->constraint_name = pstrdup(value);
+				break;
+			case PG_DIAG_SOURCE_FILE:
+				edata->filename = pstrdup(value);
+				break;
+			case PG_DIAG_SOURCE_LINE:
+				edata->lineno = pg_strtoint32(value);
+				break;
+			case PG_DIAG_SOURCE_FUNCTION:
+				edata->funcname = pstrdup(value);
+				break;
+			default:
+				elog(ERROR, "unrecognized error field code: %d", (int) code);
+				break;
+		}
+	}
+}