Introduce WaitEventSet API.

Commit ac1d7945 ("Make idle backends exit if the postmaster dies.")
introduced a regression on, at least, large linux systems. Constantly
adding the same postmaster_alive_fds to the OSs internal datastructures
for implementing poll/select can cause significant contention; leading
to a performance regression of nearly 3x in one example.

This can be avoided by using e.g. linux' epoll, which avoids having to
add/remove file descriptors to the wait datastructures at a high rate.
Unfortunately the current latch interface makes it hard to allocate any
persistent per-backend resources.

Replace, with a backward compatibility layer, WaitLatchOrSocket with a
new WaitEventSet API. Users can allocate such a Set across multiple
calls, and add more than one file-descriptor to wait on. The latter has
been added because there's upcoming postgres features where that will be
helpful.

In addition to the previously existing poll(2), select(2),
WaitForMultipleObjects() implementations also provide an epoll_wait(2)
based implementation to address the aforementioned performance
problem. Epoll is only available on linux, but that is the most likely
OS for machines large enough (four sockets) to reproduce the problem.

To actually address the aforementioned regression, create and use a
long-lived WaitEventSet for FE/BE communication.  There are additional
places that would benefit from a long-lived set, but that's a task for
another day.

Thanks to Amit Kapila, who helped make the windows code I blindly wrote
actually work.

Reported-By: Dmitry Vasilyev Discussion:
CAB-SwXZh44_2ybvS5Z67p_CDz=XFn4hNAD=CnMEF+QqkXwFrGg@mail.gmail.com
20160114143931.GG10941@awork2.anarazel.de

configure

@@ -10193,7 +10193,7 @@ fi
 ## Header files
 ##
 
-for ac_header in atomic.h crypt.h dld.h fp_class.h getopt.h ieeefp.h ifaddrs.h langinfo.h mbarrier.h poll.h pwd.h sys/ioctl.h sys/ipc.h sys/poll.h sys/pstat.h sys/resource.h sys/select.h sys/sem.h sys/shm.h sys/socket.h sys/sockio.h sys/tas.h sys/time.h sys/un.h termios.h ucred.h utime.h wchar.h wctype.h
+for ac_header in atomic.h crypt.h dld.h fp_class.h getopt.h ieeefp.h ifaddrs.h langinfo.h mbarrier.h poll.h pwd.h sys/epoll.h sys/ioctl.h sys/ipc.h sys/poll.h sys/pstat.h sys/resource.h sys/select.h sys/sem.h sys/shm.h sys/socket.h sys/sockio.h sys/tas.h sys/time.h sys/un.h termios.h ucred.h utime.h wchar.h wctype.h
 do :
   as_ac_Header=`$as_echo "ac_cv_header_$ac_header" | $as_tr_sh`
 ac_fn_c_check_header_mongrel "$LINENO" "$ac_header" "$as_ac_Header" "$ac_includes_default"

configure.in

@@ -1183,7 +1183,7 @@ AC_SUBST(UUID_LIBS)
 ##
 
 dnl sys/socket.h is required by AC_FUNC_ACCEPT_ARGTYPES
-AC_CHECK_HEADERS([atomic.h crypt.h dld.h fp_class.h getopt.h ieeefp.h ifaddrs.h langinfo.h mbarrier.h poll.h pwd.h sys/ioctl.h sys/ipc.h sys/poll.h sys/pstat.h sys/resource.h sys/select.h sys/sem.h sys/shm.h sys/socket.h sys/sockio.h sys/tas.h sys/time.h sys/un.h termios.h ucred.h utime.h wchar.h wctype.h])
+AC_CHECK_HEADERS([atomic.h crypt.h dld.h fp_class.h getopt.h ieeefp.h ifaddrs.h langinfo.h mbarrier.h poll.h pwd.h sys/epoll.h sys/ioctl.h sys/ipc.h sys/poll.h sys/pstat.h sys/resource.h sys/select.h sys/sem.h sys/shm.h sys/socket.h sys/sockio.h sys/tas.h sys/time.h sys/un.h termios.h ucred.h utime.h wchar.h wctype.h])
 
 # On BSD, test for net/if.h will fail unless sys/socket.h
 # is included first.

src/backend/libpq/be-secure.c

@@ -140,13 +140,13 @@ retry:
 	/* In blocking mode, wait until the socket is ready */
 	if (n < 0 && !port->noblock && (errno == EWOULDBLOCK || errno == EAGAIN))
 	{
-		int			w;
+		WaitEvent   event;
 
 		Assert(waitfor);
 
-		w = WaitLatchOrSocket(MyLatch,
-							  WL_LATCH_SET | WL_POSTMASTER_DEATH | waitfor,
-							  port->sock, 0);
+		ModifyWaitEvent(FeBeWaitSet, 0, waitfor, NULL);
+
+		WaitEventSetWait(FeBeWaitSet, -1 /* no timeout */, &event, 1);
 
 		/*
 		 * If the postmaster has died, it's not safe to continue running,
@@ -165,13 +165,13 @@ retry:
 		 * cycles checking for this very rare condition, and this should cause
 		 * us to exit quickly in most cases.)
 		 */
-		if (w & WL_POSTMASTER_DEATH)
+		if (event.events & WL_POSTMASTER_DEATH)
 			ereport(FATAL,
 					(errcode(ERRCODE_ADMIN_SHUTDOWN),
 					errmsg("terminating connection due to unexpected postmaster exit")));
 
 		/* Handle interrupt. */
-		if (w & WL_LATCH_SET)
+		if (event.events & WL_LATCH_SET)
 		{
 			ResetLatch(MyLatch);
 			ProcessClientReadInterrupt(true);
@@ -241,22 +241,22 @@ retry:
 
 	if (n < 0 && !port->noblock && (errno == EWOULDBLOCK || errno == EAGAIN))
 	{
-		int			w;
+		WaitEvent   event;
 
 		Assert(waitfor);
 
-		w = WaitLatchOrSocket(MyLatch,
-							  WL_LATCH_SET | WL_POSTMASTER_DEATH | waitfor,
-							  port->sock, 0);
+		ModifyWaitEvent(FeBeWaitSet, 0, waitfor, NULL);
+
+		WaitEventSetWait(FeBeWaitSet, -1 /* no timeout */, &event, 1);
 
 		/* See comments in secure_read. */
-		if (w & WL_POSTMASTER_DEATH)
+		if (event.events & WL_POSTMASTER_DEATH)
 			ereport(FATAL,
 					(errcode(ERRCODE_ADMIN_SHUTDOWN),
 					errmsg("terminating connection due to unexpected postmaster exit")));
 
 		/* Handle interrupt. */
-		if (w & WL_LATCH_SET)
+		if (event.events & WL_LATCH_SET)
 		{
 			ResetLatch(MyLatch);
 			ProcessClientWriteInterrupt(true);

src/backend/libpq/pqcomm.c

@@ -201,6 +201,11 @@ pq_init(void)
 				(errmsg("could not set socket to nonblocking mode: %m")));
 #endif
 
+	FeBeWaitSet = CreateWaitEventSet(TopMemoryContext, 3);
+	AddWaitEventToSet(FeBeWaitSet, WL_SOCKET_WRITEABLE, MyProcPort->sock,
+					  NULL, NULL);
+	AddWaitEventToSet(FeBeWaitSet, WL_LATCH_SET, -1, MyLatch, NULL);
+	AddWaitEventToSet(FeBeWaitSet, WL_POSTMASTER_DEATH, -1, NULL, NULL);
 }
 
 /* --------------------------------

src/backend/storage/ipc/latch.c

@@ -14,8 +14,8 @@
  * however reliably interrupts the sleep, and causes select() to return
  * immediately even if the signal arrives before select() begins.
  *
- * (Actually, we prefer poll() over select() where available, but the
- * same comments apply to it.)
+ * (Actually, we prefer epoll_wait() over poll() over select() where
+ * available, but the same comments apply.)
  *
  * When SetLatch is called from the same process that owns the latch,
  * SetLatch writes the byte directly to the pipe. If it's owned by another
@@ -41,6 +41,9 @@
 #include <unistd.h>
 #include <sys/time.h>
 #include <sys/types.h>
+#ifdef HAVE_SYS_EPOLL_H
+#include <sys/epoll.h>
+#endif
 #ifdef HAVE_POLL_H
 #include <poll.h>
 #endif
@@ -65,18 +68,59 @@
  * useful to manually specify the used primitive.  If desired, just add a
  * define somewhere before this block.
  */
-#if defined(LATCH_USE_POLL) || defined(LATCH_USE_SELECT) \
-	|| defined(LATCH_USE_WIN32)
+#if defined(WAIT_USE_EPOLL) || defined(WAIT_USE_POLL) || \
+	defined(WAIT_USE_SELECT) || defined(WAIT_USE_WIN32)
 /* don't overwrite manual choice */
+#elif defined(HAVE_SYS_EPOLL_H)
+#define WAIT_USE_EPOLL
 #elif defined(HAVE_POLL)
-#define LATCH_USE_POLL
+#define WAIT_USE_POLL
 #elif HAVE_SYS_SELECT_H
-#define LATCH_USE_SELECT
+#define WAIT_USE_SELECT
 #elif WIN32
-#define LATCH_USE_WIN32
+#define WAIT_USE_WIN32
 #else
-#error "no latch implementation available"
+#error "no wait set implementation available"
+#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;
+
+#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_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
+};
 
 #ifndef WIN32
 /* Are we currently in WaitLatch? The signal handler would like to know. */
@@ -91,6 +135,16 @@ static void sendSelfPipeByte(void);
 static void drainSelfPipe(void);
 #endif   /* WIN32 */
 
+#if defined(WAIT_USE_EPOLL)
+static void WaitEventAdjustEpoll(WaitEventSet *set, WaitEvent *event, int action);
+#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 int WaitEventSetWaitBlock(WaitEventSet *set, int cur_timeout,
+					  WaitEvent *occurred_events, int nevents);
 
 /*
  * Initialize the process-local latch infrastructure.
@@ -255,642 +309,1181 @@ WaitLatch(volatile Latch *latch, int wakeEvents, long timeout)
  * When waiting on a socket, EOF and error conditions are reported by
  * returning the socket as readable/writable or both, depending on
  * WL_SOCKET_READABLE/WL_SOCKET_WRITEABLE being specified.
+ *
+ * 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.
  */
-#ifndef LATCH_USE_WIN32
 int
 WaitLatchOrSocket(volatile Latch *latch, int wakeEvents, pgsocket sock,
 				  long timeout)
 {
-	int			result = 0;
+	int			ret = 0;
 	int			rc;
-	instr_time	start_time,
-				cur_time;
-	long		cur_timeout;
-
-#if defined(LATCH_USE_POLL)
-	struct pollfd pfds[3];
-	int			nfds;
-#elif defined(LATCH_USE_SELECT)
-	struct timeval tv,
-			   *tvp;
-	fd_set		input_mask;
-	fd_set		output_mask;
-	int			hifd;
-#endif
+	WaitEvent	event;
+	WaitEventSet *set = CreateWaitEventSet(CurrentMemoryContext, 3);
 
-	Assert(wakeEvents != 0);	/* must have at least one wake event */
+	if (wakeEvents & WL_TIMEOUT)
+		Assert(timeout >= 0);
+	else
+		timeout = -1;
 
-	/* waiting for socket readiness without a socket indicates a bug */
-	if (sock == PGINVALID_SOCKET &&
-		(wakeEvents & (WL_SOCKET_READABLE | WL_SOCKET_WRITEABLE)) != 0)
-		elog(ERROR, "cannot wait on socket event without a socket");
+	if (wakeEvents & WL_LATCH_SET)
+		AddWaitEventToSet(set, WL_LATCH_SET, PGINVALID_SOCKET,
+						  (Latch *) latch, NULL);
 
-	if ((wakeEvents & WL_LATCH_SET) && latch->owner_pid != MyProcPid)
-		elog(ERROR, "cannot wait on a latch owned by another process");
+	if (wakeEvents & WL_POSTMASTER_DEATH)
+		AddWaitEventToSet(set, WL_POSTMASTER_DEATH, PGINVALID_SOCKET,
+						  NULL, NULL);
 
-	/*
-	 * Initialize timeout if requested.  We must record the current time so
-	 * that we can determine the remaining timeout if the poll() or select()
-	 * is interrupted.  (On some platforms, select() will update the contents
-	 * of "tv" for us, but unfortunately we can't rely on that.)
-	 */
-	if (wakeEvents & WL_TIMEOUT)
+	if (wakeEvents & (WL_SOCKET_READABLE | WL_SOCKET_WRITEABLE))
 	{
-		INSTR_TIME_SET_CURRENT(start_time);
-		Assert(timeout >= 0 && timeout <= INT_MAX);
-		cur_timeout = timeout;
+		int			ev;
 
-#ifdef LATCH_USE_SELECT
-		tv.tv_sec = cur_timeout / 1000L;
-		tv.tv_usec = (cur_timeout % 1000L) * 1000L;
-		tvp = &tv;
-#endif
+		ev = wakeEvents & (WL_SOCKET_READABLE | WL_SOCKET_WRITEABLE);
+		AddWaitEventToSet(set, ev, sock, NULL, NULL);
 	}
+
+	rc = WaitEventSetWait(set, timeout, &event, 1);
+
+	if (rc == 0)
+		ret |= WL_TIMEOUT;
 	else
 	{
-		cur_timeout = -1;
+		ret |= event.events & (WL_LATCH_SET |
+							   WL_POSTMASTER_DEATH |
+							   WL_SOCKET_READABLE |
+							   WL_SOCKET_WRITEABLE);
+	}
+
+	FreeWaitEventSet(set);
+
+	return ret;
+}
 
-#ifdef LATCH_USE_SELECT
-		tvp = NULL;
+/*
+ * 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(volatile Latch *latch)
+{
+#ifndef WIN32
+	pid_t		owner_pid;
+#else
+	HANDLE		handle;
 #endif
-	}
 
-	waiting = true;
-	do
+	/*
+	 * The memory barrier has be 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;
+
+#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 to wake up the select()
+	 * 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 (waiting)
+			sendSelfPipeByte();
+	}
+	else
+		kill(owner_pid, SIGUSR1);
+#else
+
 	/*
-		 * Check if the latch is set already. If so, leave 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 poll()/select()
-		 * below, the setter will write a byte to the pipe (or signal us and
-		 * the signal handler will do that), and the poll()/select() will
-		 * return immediately.
-		 *
-		 * 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_sigusr1_handler().
+	 * See if anyone's waiting for the latch. It can be the current process if
+	 * we're in a signal handler.
 	 *
-		 * Note: we assume that the kernel calls involved in drainSelfPipe()
-		 * and SetLatch() will provide adequate synchronization on machines
-		 * with weak memory ordering, so that we cannot miss seeing is_set if
-		 * the signal byte is already in the pipe when we drain it.
+	 * Use a local variable here just in case somebody changes the event field
+	 * concurrently (which really should not happen).
 	 */
-		if ((wakeEvents & WL_LATCH_SET) && latch->is_set)
+	handle = latch->event;
+	if (handle)
 	{
-			result |= WL_LATCH_SET;
-			break;
+		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(volatile Latch *latch)
+{
+	/* Only the owner should reset the latch */
+	Assert(latch->owner_pid == MyProcPid);
+
+	latch->is_set = false;
 
 	/*
-		 * Must wait ... we use the polling interface determined at the top of
-		 * this file to do so.
+	 * 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.
 	 */
-#if defined(LATCH_USE_POLL)
-		nfds = 0;
+	pg_memory_barrier();
+}
 
-		/* selfpipe is always in pfds[0] */
-		pfds[0].fd = selfpipe_readfd;
-		pfds[0].events = POLLIN;
-		pfds[0].revents = 0;
-		nfds++;
+/*
+ * Create a WaitEventSet with space for nevents different events to wait for.
+ *
+ * These events can then efficiently waited upon together, using
+ * WaitEventSetWait().
+ */
+WaitEventSet *
+CreateWaitEventSet(MemoryContext context, int nevents)
+{
+	WaitEventSet *set;
+	char	   *data;
+	Size		sz = 0;
+
+	sz += sizeof(WaitEventSet);
+	sz += sizeof(WaitEvent) * nevents;
+
+#if defined(WAIT_USE_EPOLL)
+	sz += sizeof(struct epoll_event) * nevents;
+#elif defined(WAIT_USE_POLL)
+	sz += sizeof(struct pollfd) * nevents;
+#elif defined(WAIT_USE_WIN32)
+	/* need space for the pgwin32_signal_event */
+	sz += sizeof(HANDLE) * (nevents + 1);
+#endif
 
-		if (wakeEvents & (WL_SOCKET_READABLE | WL_SOCKET_WRITEABLE))
-		{
-			/* socket, if used, is always in pfds[1] */
-			pfds[1].fd = sock;
-			pfds[1].events = 0;
-			if (wakeEvents & WL_SOCKET_READABLE)
-				pfds[1].events |= POLLIN;
-			if (wakeEvents & WL_SOCKET_WRITEABLE)
-				pfds[1].events |= POLLOUT;
-			pfds[1].revents = 0;
-			nfds++;
-		}
+	data = (char *) MemoryContextAllocZero(context, sz);
 
-		if (wakeEvents & WL_POSTMASTER_DEATH)
-		{
-			/* postmaster fd, if used, is always in pfds[nfds - 1] */
-			pfds[nfds].fd = postmaster_alive_fds[POSTMASTER_FD_WATCH];
-			pfds[nfds].events = POLLIN;
-			pfds[nfds].revents = 0;
-			nfds++;
-		}
+	set = (WaitEventSet *) data;
+	data += sizeof(WaitEventSet);
 
-		/* Sleep */
-		rc = poll(pfds, nfds, (int) cur_timeout);
+	set->events = (WaitEvent *) data;
+	data += sizeof(WaitEvent) * nevents;
 
-		/* Check return code */
-		if (rc < 0)
+#if defined(WAIT_USE_EPOLL)
+	set->epoll_ret_events = (struct epoll_event *) data;
+	data += sizeof(struct epoll_event) * nevents;
+#elif defined(WAIT_USE_POLL)
+	set->pollfds = (struct pollfd *) data;
+	data += sizeof(struct pollfd) * nevents;
+#elif defined(WAIT_USE_WIN32)
+	set->handles = (HANDLE) data;
+	data += sizeof(HANDLE) * nevents;
+#endif
+
+	set->latch = NULL;
+	set->nevents_space = nevents;
+
+#if defined(WAIT_USE_EPOLL)
+	set->epoll_fd = epoll_create(nevents);
+	if (set->epoll_fd < 0)
+		elog(ERROR, "epoll_create failed: %m");
+#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.
+ */
+void
+FreeWaitEventSet(WaitEventSet *set)
+{
+#if defined(WAIT_USE_EPOLL)
+	close(set->epoll_fd);
+#elif defined(WAIT_USE_WIN32)
+	WaitEvent  *cur_event;
+
+	for (cur_event = set->events;
+		 cur_event < (set->events + set->nevents);
+		 cur_event++)
 	{
-			/* EINTR is okay, otherwise complain */
-			if (errno != EINTR)
+		if (cur_event->events & WL_LATCH_SET)
 		{
-				waiting = false;
-				ereport(ERROR,
-						(errcode_for_socket_access(),
-						 errmsg("poll() failed: %m")));
-			}
+			/* uses the latch's HANDLE */
 		}
-		else if (rc == 0)
+		else if (cur_event->events & WL_POSTMASTER_DEATH)
 		{
-			/* timeout exceeded */
-			if (wakeEvents & WL_TIMEOUT)
-				result |= WL_TIMEOUT;
+			/* uses PostmasterHandle */
 		}
 		else
 		{
-			/* at least one event occurred, so check revents values */
+			/* 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);
+}
+
+/* ---
+ * 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 WL_SOCKET_WRITEABLE
+ * - WL_SOCKET_WRITEABLE: Wait for socket to become writeable
+ *	 can be combined with WL_SOCKET_READABLE
+ *
+ * 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 backend-local latch initialized with InitLatch, or a
+ * shared latch associated with the current process by calling OwnLatch.
+ *
+ * In the WL_SOCKET_READABLE/WRITEABLE case, EOF and error conditions are
+ * reported by returning the socket as readable/writable or both, depending on
+ * WL_SOCKET_READABLE/WRITEABLE being specified.
+ *
+ * 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 (pfds[0].revents & POLLIN)
+	if (latch)
 	{
-				/* There's data in the self-pipe, clear it. */
-				drainSelfPipe();
+		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 spuport being set");
 	}
-
-			if ((wakeEvents & WL_SOCKET_READABLE) &&
-				(pfds[1].revents & POLLIN))
+	else
 	{
-				/* data available in socket, or EOF/error condition */
-				result |= WL_SOCKET_READABLE;
+		if (events & WL_LATCH_SET)
+			elog(ERROR, "cannot wait on latch without a specified latch");
 	}
-			if ((wakeEvents & WL_SOCKET_WRITEABLE) &&
-				(pfds[1].revents & POLLOUT))
+
+	/* waiting for socket readiness without a socket indicates a bug */
+	if (fd == PGINVALID_SOCKET &&
+		(events & (WL_SOCKET_READABLE | WL_SOCKET_WRITEABLE)))
+		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;
+
+	if (events == WL_LATCH_SET)
 	{
-				/* socket is writable */
-				result |= WL_SOCKET_WRITEABLE;
+		set->latch = latch;
+		set->latch_pos = event->pos;
+#ifndef WIN32
+		event->fd = selfpipe_readfd;
+#endif
 	}
-			if ((wakeEvents & (WL_SOCKET_READABLE | WL_SOCKET_WRITEABLE)) &&
-				(pfds[1].revents & (POLLHUP | POLLERR | POLLNVAL)))
+	else if (events == WL_POSTMASTER_DEATH)
 	{
-				/* EOF/error condition */
-				if (wakeEvents & WL_SOCKET_READABLE)
-					result |= WL_SOCKET_READABLE;
-				if (wakeEvents & WL_SOCKET_WRITEABLE)
-					result |= WL_SOCKET_WRITEABLE;
+#ifndef WIN32
+		event->fd = postmaster_alive_fds[POSTMASTER_FD_WATCH];
+#endif
 	}
 
-			/*
-			 * We expect a 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.
-			 */
-			if ((wakeEvents & WL_POSTMASTER_DEATH) &&
-				(pfds[nfds - 1].revents & (POLLHUP | POLLIN | POLLERR | POLLNVAL)))
-			{
-				/*
-				 * According to the select(2) man page on Linux, select(2) may
-				 * spuriously return and report a file descriptor as readable,
-				 * when it's not; and presumably so can poll(2).  It's not
-				 * clear that the relevant cases would ever apply to the
-				 * postmaster pipe, but since the consequences of falsely
-				 * returning WL_POSTMASTER_DEATH could be pretty unpleasant,
-				 * we take the trouble to positively verify EOF with
-				 * PostmasterIsAlive().
+	/* perform wait primitive specific initialization, if needed */
+#if defined(WAIT_USE_EPOLL)
+	WaitEventAdjustEpoll(set, event, EPOLL_CTL_ADD);
+#elif defined(WAIT_USE_POLL)
+	WaitEventAdjustPoll(set, event);
+#elif defined(WAIT_USE_SELECT)
+	/* nothing to do */
+#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.
+ *
+ * 'pos' is the id returned by AddWaitEventToSet.
  */
-				if (!PostmasterIsAlive())
-					result |= WL_POSTMASTER_DEATH;
-			}
-		}
-#elif defined(LATCH_USE_SELECT)
+void
+ModifyWaitEvent(WaitEventSet *set, int pos, uint32 events, Latch *latch)
+{
+	WaitEvent  *event;
+
+	Assert(pos < set->nevents);
+
+	event = &set->events[pos];
 
 	/*
-		 * On at least older linux kernels select(), in violation of POSIX,
-		 * doesn't reliably return a socket as writable if closed - but we
-		 * rely on that. So far all the known cases of this problem are on
-		 * platforms that also provide a poll() implementation without that
-		 * bug.  If we find one where that's not the case, we'll need to add a
-		 * workaround.
+	 * 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.
 	 */
-		FD_ZERO(&input_mask);
-		FD_ZERO(&output_mask);
-
-		FD_SET(selfpipe_readfd, &input_mask);
-		hifd = selfpipe_readfd;
+	if (events == event->events &&
+		(!(event->events & WL_LATCH_SET) || set->latch == latch))
+		return;
 
-		if (wakeEvents & WL_POSTMASTER_DEATH)
+	if (event->events & WL_LATCH_SET &&
+		events != event->events)
 	{
-			FD_SET(postmaster_alive_fds[POSTMASTER_FD_WATCH], &input_mask);
-			if (postmaster_alive_fds[POSTMASTER_FD_WATCH] > hifd)
-				hifd = postmaster_alive_fds[POSTMASTER_FD_WATCH];
+		/* we could allow to disable latch events for a while */
+		elog(ERROR, "cannot modify latch event");
 	}
 
-		if (wakeEvents & WL_SOCKET_READABLE)
+	if (event->events & WL_POSTMASTER_DEATH)
 	{
-			FD_SET(sock, &input_mask);
-			if (sock > hifd)
-				hifd = sock;
+		elog(ERROR, "cannot modify postmaster death event");
 	}
 
-		if (wakeEvents & WL_SOCKET_WRITEABLE)
+	/* FIXME: validate event mask */
+	event->events = events;
+
+	if (events == WL_LATCH_SET)
 	{
-			FD_SET(sock, &output_mask);
-			if (sock > hifd)
-				hifd = sock;
+		set->latch = latch;
 	}
 
-		/* Sleep */
-		rc = select(hifd + 1, &input_mask, &output_mask, NULL, tvp);
+#if defined(WAIT_USE_EPOLL)
+	WaitEventAdjustEpoll(set, event, EPOLL_CTL_MOD);
+#elif defined(WAIT_USE_POLL)
+	WaitEventAdjustPoll(set, event);
+#elif defined(WAIT_USE_SELECT)
+	/* nothing to do */
+#elif defined(WAIT_USE_WIN32)
+	WaitEventAdjustWin32(set, event);
+#endif
+}
 
-		/* Check return code */
-		if (rc < 0)
-		{
-			/* EINTR is okay, otherwise complain */
-			if (errno != EINTR)
+#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)
 	{
-				waiting = false;
+		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));
+
+		if (event->events & WL_SOCKET_READABLE)
+			epoll_ev.events |= EPOLLIN;
+		if (event->events & WL_SOCKET_WRITEABLE)
+			epoll_ev.events |= EPOLLOUT;
+	}
+
+	/*
+	 * 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("select() failed: %m")));
-			}
+				 errmsg("epoll_ctl() failed: %m")));
+}
+#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 (rc == 0)
+	else if (event->events == WL_POSTMASTER_DEATH)
 	{
-			/* timeout exceeded */
-			if (wakeEvents & WL_TIMEOUT)
-				result |= WL_TIMEOUT;
+		pollfd->events = POLLIN;
 	}
 	else
 	{
-			/* at least one event occurred, so check masks */
-			if (FD_ISSET(selfpipe_readfd, &input_mask))
-			{
-				/* There's data in the self-pipe, clear it. */
-				drainSelfPipe();
+		Assert(event->events & (WL_SOCKET_READABLE | WL_SOCKET_WRITEABLE));
+		pollfd->events = 0;
+		if (event->events & WL_SOCKET_READABLE)
+			pollfd->events |= POLLIN;
+		if (event->events & WL_SOCKET_WRITEABLE)
+			pollfd->events |= POLLOUT;
 	}
-			if ((wakeEvents & WL_SOCKET_READABLE) && FD_ISSET(sock, &input_mask))
+
+	Assert(event->fd != PGINVALID_SOCKET);
+}
+#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)
 	{
-				/* data available in socket, or EOF */
-				result |= WL_SOCKET_READABLE;
+		Assert(set->latch != NULL);
+		*handle = set->latch->event;
 	}
-			if ((wakeEvents & WL_SOCKET_WRITEABLE) && FD_ISSET(sock, &output_mask))
+	else if (event->events == WL_POSTMASTER_DEATH)
 	{
-				/* socket is writable, or EOF */
-				result |= WL_SOCKET_WRITEABLE;
+		*handle = PostmasterHandle;
 	}
-			if ((wakeEvents & WL_POSTMASTER_DEATH) &&
-				FD_ISSET(postmaster_alive_fds[POSTMASTER_FD_WATCH],
-						 &input_mask))
+	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 (*handle == WSA_INVALID_EVENT)
 		{
+			*handle = WSACreateEvent();
+			if (*handle == WSA_INVALID_EVENT)
+				elog(ERROR, "failed to create event for socket: error code %u",
+					 WSAGetLastError());
+		}
+		if (WSAEventSelect(event->fd, *handle, flags) != 0)
+			elog(ERROR, "failed to set up event for socket: error code %u",
+				 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 miliseconds.
+ *
+ * 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)
+{
+	int			returned_events = 0;
+	instr_time	start_time;
+	instr_time	cur_time;
+	long		cur_timeout = -1;
+
+	Assert(nevents > 0);
+
 	/*
-				 * According to the select(2) man page on Linux, select(2) may
-				 * spuriously return and report a file descriptor as readable,
-				 * when it's not; and presumably so can poll(2).  It's not
-				 * clear that the relevant cases would ever apply to the
-				 * postmaster pipe, but since the consequences of falsely
-				 * returning WL_POSTMASTER_DEATH could be pretty unpleasant,
-				 * we take the trouble to positively verify EOF with
-				 * PostmasterIsAlive().
+	 * Initialize timeout if requested.  We must record the current time so
+	 * that we can determine the remaining timeout if interrupted.
 	 */
-				if (!PostmasterIsAlive())
-					result |= WL_POSTMASTER_DEATH;
+	if (timeout >= 0)
+	{
+		INSTR_TIME_SET_CURRENT(start_time);
+		Assert(timeout >= 0 && timeout <= INT_MAX);
+		cur_timeout = timeout;
 	}
+
+#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_sigusr1_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)
+		{
+			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++;
+
+			break;
 		}
-#endif   /* LATCH_USE_SELECT */
 
 		/*
-		 * Check again whether latch is set, the arrival of a signal/self-byte
-		 * might be what stopped our sleep. It's not required for correctness
-		 * to signal the latch as being set (we'd just loop if there's no
-		 * other event), but it seems good to report an arrived latch asap.
-		 * This way we also don't have to compute the current timestamp again.
+		 * 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.
 		 */
-		if ((wakeEvents & WL_LATCH_SET) && latch->is_set)
-			result |= WL_LATCH_SET;
+		rc = WaitEventSetWaitBlock(set, cur_timeout,
+								   occurred_events, nevents);
+
+		if (rc == -1)
+			break;				/* timeout occurred */
+		else
+			returned_events = rc;
 
 		/* If we're not done, update cur_timeout for next iteration */
-		if (result == 0 && (wakeEvents & WL_TIMEOUT))
+		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)
-			{
-				/* Timeout has expired, no need to continue looping */
-				result |= WL_TIMEOUT;
-			}
-#ifdef LATCH_USE_SELECT
-			else
-			{
-				tv.tv_sec = cur_timeout / 1000L;
-				tv.tv_usec = (cur_timeout % 1000L) * 1000L;
+				break;
 		}
-#endif
 	}
-	} while (result == 0);
+#ifndef WIN32
 	waiting = false;
+#endif
 
-	return result;
+	return returned_events;
 }
-#else							/* LATCH_USE_WIN32 */
-int
-WaitLatchOrSocket(volatile Latch *latch, int wakeEvents, pgsocket sock,
-				  long timeout)
+
+
+#if defined(WAIT_USE_EPOLL)
+
+/*
+ * Wait using linux's epoll_wait(2).
+ *
+ * This is the preferrable 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 int
+WaitEventSetWaitBlock(WaitEventSet *set, int cur_timeout,
+					  WaitEvent *occurred_events, int nevents)
 {
-	DWORD		rc;
-	instr_time	start_time,
-				cur_time;
-	long		cur_timeout;
-	HANDLE		events[4];
-	HANDLE		latchevent;
-	HANDLE		sockevent = WSA_INVALID_EVENT;
-	int			numevents;
-	int			result = 0;
-	int			pmdeath_eventno = 0;
-
-	Assert(wakeEvents != 0);	/* must have at least one wake event */
+	int			returned_events = 0;
+	int			rc;
+	WaitEvent  *cur_event;
+	struct epoll_event *cur_epoll_event;
 
-	/* waiting for socket readiness without a socket indicates a bug */
-	if (sock == PGINVALID_SOCKET &&
-		(wakeEvents & (WL_SOCKET_READABLE | WL_SOCKET_WRITEABLE)) != 0)
-		elog(ERROR, "cannot wait on socket event without a socket");
+	/* Sleep */
+	rc = epoll_wait(set->epoll_fd, set->epoll_ret_events,
+					nevents, cur_timeout);
 
-	if ((wakeEvents & WL_LATCH_SET) && latch->owner_pid != MyProcPid)
-		elog(ERROR, "cannot wait on a latch owned by another process");
+	/* Check return code */
+	if (rc < 0)
+	{
+		/* EINTR is okay, otherwise complain */
+		if (errno != EINTR)
+		{
+			waiting = false;
+			ereport(ERROR,
+					(errcode_for_socket_access(),
+					 errmsg("epoll_wait() failed: %m")));
+		}
+		return 0;
+	}
+	else if (rc == 0)
+	{
+		/* timeout exceeded */
+		return -1;
+	}
 
 	/*
-	 * Initialize timeout if requested.  We must record the current time so
-	 * that we can determine the remaining timeout if WaitForMultipleObjects
-	 * is interrupted.
+	 * 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.
 	 */
-	if (wakeEvents & WL_TIMEOUT)
+	for (cur_epoll_event = set->epoll_ret_events;
+		 cur_epoll_event < (set->epoll_ret_events + rc) &&
+		 returned_events < nevents;
+		 cur_epoll_event++)
 	{
-		INSTR_TIME_SET_CURRENT(start_time);
-		Assert(timeout >= 0 && timeout <= INT_MAX);
-		cur_timeout = timeout;
-	}
-	else
-		cur_timeout = INFINITE;
+		/* 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))
+		{
+			/* There's data in the self-pipe, clear it. */
+			drainSelfPipe();
 
+			if (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))
+		{
 			/*
-	 * Construct an array of event handles for WaitforMultipleObjects().
+			 * 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.
 			 *
-	 * 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.
+			 * As explained in the WAIT_USE_SELECT implementation, select(2)
+			 * may spuriously return. Be paranoid about that here too, a
+			 * spurious WL_POSTMASTER_DEATH would be painful.
 			 */
-	latchevent = latch->event;
+			if (!PostmasterIsAlive())
+			{
+				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))
+		{
+			Assert(cur_event->fd != PGINVALID_SOCKET);
 
-	events[0] = pgwin32_signal_event;
-	events[1] = latchevent;
-	numevents = 2;
-	if (wakeEvents & (WL_SOCKET_READABLE | WL_SOCKET_WRITEABLE))
+			if ((cur_event->events & WL_SOCKET_READABLE) &&
+				(cur_epoll_event->events & (EPOLLIN | EPOLLERR | EPOLLHUP)))
 			{
-		/* Need an event object to represent events on the socket */
-		int			flags = FD_CLOSE;	/* always check for errors/EOF */
+				/* data available in socket, or EOF */
+				occurred_events->events |= WL_SOCKET_READABLE;
+			}
 
-		if (wakeEvents & WL_SOCKET_READABLE)
-			flags |= FD_READ;
-		if (wakeEvents & WL_SOCKET_WRITEABLE)
-			flags |= FD_WRITE;
+			if ((cur_event->events & WL_SOCKET_WRITEABLE) &&
+				(cur_epoll_event->events & (EPOLLOUT | EPOLLERR | EPOLLHUP)))
+			{
+				/* writable, or EOF */
+				occurred_events->events |= WL_SOCKET_WRITEABLE;
+			}
 
-		sockevent = WSACreateEvent();
-		if (sockevent == WSA_INVALID_EVENT)
-			elog(ERROR, "failed to create event for socket: error code %u",
-				 WSAGetLastError());
-		if (WSAEventSelect(sock, sockevent, flags) != 0)
-			elog(ERROR, "failed to set up event for socket: error code %u",
-				 WSAGetLastError());
+			if (occurred_events->events != 0)
+			{
+				occurred_events->fd = cur_event->fd;
+				occurred_events++;
+				returned_events++;
+			}
+		}
+	}
 
-		events[numevents++] = sockevent;
+	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("poll() failed: %m")));
 		}
-	if (wakeEvents & WL_POSTMASTER_DEATH)
+		return 0;
+	}
+	else if (rc == 0)
 	{
-		pmdeath_eventno = numevents;
-		events[numevents++] = PostmasterHandle;
+		/* timeout exceeded */
+		return -1;
 	}
 
-	/* Ensure that signals are serviced even if latch is already set */
-	pgwin32_dispatch_queued_signals();
-
-	do
+	for (cur_event = set->events, cur_pollfd = set->pollfds;
+		 cur_event < (set->events + set->nevents) &&
+		 returned_events < nevents;
+		 cur_event++, cur_pollfd++)
 	{
-		/*
-		 * The comment in the unix version above applies here as well. At
-		 * least after mentally replacing self-pipe with windows event.
-		 * There's no danger of overflowing, as "Setting an event that is
-		 * already set has no effect.".
-		 */
-		if ((wakeEvents & WL_LATCH_SET) && latch->is_set)
+		/* 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)))
 		{
-			result |= WL_LATCH_SET;
+			/* There's data in the self-pipe, clear it. */
+			drainSelfPipe();
 
+			if (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)))
+		{
 			/*
-			 * Leave loop immediately, avoid blocking again. We don't attempt
-			 * to report any other events that might also be satisfied.
+			 * 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.
+			 *
+			 * As explained in the WAIT_USE_SELECT implementation, select(2)
+			 * may spuriously return. Be paranoid about that here too, a
+			 * spurious WL_POSTMASTER_DEATH would be painful.
 			 */
-			break;
+			if (!PostmasterIsAlive())
+			{
+				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))
+		{
+			int			errflags = POLLHUP | POLLERR | POLLNVAL;
 
-		rc = WaitForMultipleObjects(numevents, events, FALSE, cur_timeout);
+			Assert(cur_event->fd >= PGINVALID_SOCKET);
 
-		if (rc == WAIT_FAILED)
-			elog(ERROR, "WaitForMultipleObjects() failed: error code %lu",
-				 GetLastError());
-		else if (rc == WAIT_TIMEOUT)
+			if ((cur_event->events & WL_SOCKET_READABLE) &&
+				(cur_pollfd->revents & (POLLIN | errflags)))
 			{
-			result |= WL_TIMEOUT;
+				/* data available in socket, or EOF */
+				occurred_events->events |= WL_SOCKET_READABLE;
 			}
-		else if (rc == WAIT_OBJECT_0)
+
+			if ((cur_event->events & WL_SOCKET_WRITEABLE) &&
+				(cur_pollfd->revents & (POLLOUT | errflags)))
 			{
-			/* Service newly-arrived signals */
-			pgwin32_dispatch_queued_signals();
+				/* writeable, or EOF */
+				occurred_events->events |= WL_SOCKET_WRITEABLE;
 			}
-		else if (rc == WAIT_OBJECT_0 + 1)
+
+			if (occurred_events->events != 0)
 			{
+				occurred_events->fd = cur_event->fd;
+				occurred_events++;
+				returned_events++;
+			}
+		}
+	}
+	return returned_events;
+}
+
+#elif defined(WAIT_USE_SELECT)
+
+/*
+ * Wait using select(2).
+ *
+ * XXX: On at least older linux kernels select(), in violation of POSIX,
+ * doesn't reliably return a socket as writable if closed - but we rely on
+ * that. So far all the known cases of this problem are on platforms that also
+ * provide a poll() implementation without that bug.  If we find one where
+ * that's not the case, we'll need to add a workaround.
+ */
+static inline int
+WaitEventSetWaitBlock(WaitEventSet *set, int cur_timeout,
+					  WaitEvent *occurred_events, int nevents)
+{
+	int			returned_events = 0;
+	int			rc;
+	WaitEvent  *cur_event;
+	fd_set		input_mask;
+	fd_set		output_mask;
+	int			hifd;
+	struct timeval tv;
+	struct timeval *tvp = NULL;
+
+	FD_ZERO(&input_mask);
+	FD_ZERO(&output_mask);
+
 	/*
-			 * Reset the event.  We'll re-check the, potentially, set latch on
-			 * next iteration of loop, but let's not waste the cycles to
-			 * update cur_timeout below.
+	 * Prepare input/output masks. We do so every loop iteration as there's no
+	 * entirely portable way to copy fd_sets.
 	 */
-			if (!ResetEvent(latchevent))
-				elog(ERROR, "ResetEvent failed: error code %lu", GetLastError());
+	for (cur_event = set->events;
+		 cur_event < (set->events + set->nevents);
+		 cur_event++)
+	{
+		if (cur_event->events == WL_LATCH_SET)
+			FD_SET(cur_event->fd, &input_mask);
+		else if (cur_event->events == WL_POSTMASTER_DEATH)
+			FD_SET(cur_event->fd, &input_mask);
+		else
+		{
+			Assert(cur_event->events & (WL_SOCKET_READABLE | WL_SOCKET_WRITEABLE));
+			if (cur_event->events == WL_SOCKET_READABLE)
+				FD_SET(cur_event->fd, &input_mask);
+			else if (cur_event->events == WL_SOCKET_WRITEABLE)
+				FD_SET(cur_event->fd, &output_mask);
+		}
 
-			continue;
+		if (cur_event->fd > hifd)
+			hifd = cur_event->fd;
 	}
-		else if ((wakeEvents & (WL_SOCKET_READABLE | WL_SOCKET_WRITEABLE)) &&
-				 rc == WAIT_OBJECT_0 + 2)		/* socket is at event slot 2 */
+
+	/* Sleep */
+	if (cur_timeout >= 0)
 	{
-			WSANETWORKEVENTS resEvents;
+		tv.tv_sec = cur_timeout / 1000L;
+		tv.tv_usec = (cur_timeout % 1000L) * 1000L;
+		tvp = &tv;
+	}
+	rc = select(hifd + 1, &input_mask, &output_mask, NULL, tvp);
 
-			ZeroMemory(&resEvents, sizeof(resEvents));
-			if (WSAEnumNetworkEvents(sock, sockevent, &resEvents) != 0)
-				elog(ERROR, "failed to enumerate network events: error code %u",
-					 WSAGetLastError());
-			if ((wakeEvents & WL_SOCKET_READABLE) &&
-				(resEvents.lNetworkEvents & FD_READ))
+	/* Check return code */
+	if (rc < 0)
+	{
+		/* EINTR is okay, otherwise complain */
+		if (errno != EINTR)
 		{
-				result |= WL_SOCKET_READABLE;
+			waiting = false;
+			ereport(ERROR,
+					(errcode_for_socket_access(),
+					 errmsg("select() failed: %m")));
 		}
-			if ((wakeEvents & WL_SOCKET_WRITEABLE) &&
-				(resEvents.lNetworkEvents & FD_WRITE))
+		return 0;				/* retry */
+	}
+	else if (rc == 0)
 	{
-				result |= WL_SOCKET_WRITEABLE;
+		/* timeout exceeded */
+		return -1;
 	}
-			if (resEvents.lNetworkEvents & FD_CLOSE)
+
+	/*
+	 * To associate events with select's masks, we have to check the status of
+	 * the file descriptors associated with an event; by looping through all
+	 * events.
+	 */
+	for (cur_event = set->events;
+		 cur_event < (set->events + set->nevents)
+		 && returned_events < nevents;
+		 cur_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 &&
+			FD_ISSET(cur_event->fd, &input_mask))
 		{
-				if (wakeEvents & WL_SOCKET_READABLE)
-					result |= WL_SOCKET_READABLE;
-				if (wakeEvents & WL_SOCKET_WRITEABLE)
-					result |= WL_SOCKET_WRITEABLE;
+			/* There's data in the self-pipe, clear it. */
+			drainSelfPipe();
+
+			if (set->latch->is_set)
+			{
+				occurred_events->fd = PGINVALID_SOCKET;
+				occurred_events->events = WL_LATCH_SET;
+				occurred_events++;
+				returned_events++;
 			}
 		}
-		else if ((wakeEvents & WL_POSTMASTER_DEATH) &&
-				 rc == WAIT_OBJECT_0 + pmdeath_eventno)
+		else if (cur_event->events == WL_POSTMASTER_DEATH &&
+				 FD_ISSET(cur_event->fd, &input_mask))
 		{
 			/*
-			 * 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.
+			 * According to the select(2) man page on Linux, select(2) may
+			 * spuriously return and report a file descriptor as readable,
+			 * when it's not; and presumably so can poll(2).  It's not clear
+			 * that the relevant cases would ever apply to the postmaster
+			 * pipe, but since the consequences of falsely returning
+			 * WL_POSTMASTER_DEATH could be pretty unpleasant, we take the
+			 * trouble to positively verify EOF with PostmasterIsAlive().
 			 */
 			if (!PostmasterIsAlive())
-				result |= WL_POSTMASTER_DEATH;
+			{
+				occurred_events->fd = PGINVALID_SOCKET;
+				occurred_events->events = WL_POSTMASTER_DEATH;
+				occurred_events++;
+				returned_events++;
 			}
-		else
-			elog(ERROR, "unexpected return code from WaitForMultipleObjects(): %lu", rc);
-
-		/* If we're not done, update cur_timeout for next iteration */
-		if (result == 0 && (wakeEvents & WL_TIMEOUT))
+		}
+		else if (cur_event->events & (WL_SOCKET_READABLE | WL_SOCKET_WRITEABLE))
 		{
-			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)
+			Assert(cur_event->fd != PGINVALID_SOCKET);
+
+			if ((cur_event->events & WL_SOCKET_READABLE) &&
+				FD_ISSET(cur_event->fd, &input_mask))
 			{
-				/* Timeout has expired, no need to continue looping */
-				result |= WL_TIMEOUT;
-			}
+				/* data available in socket, or EOF */
+				occurred_events->events |= WL_SOCKET_READABLE;
 			}
-	} while (result == 0);
 
-	/* Clean up the event object we created for the socket */
-	if (sockevent != WSA_INVALID_EVENT)
+			if ((cur_event->events & WL_SOCKET_WRITEABLE) &&
+				FD_ISSET(cur_event->fd, &output_mask))
 			{
-		WSAEventSelect(sock, NULL, 0);
-		WSACloseEvent(sockevent);
+				/* socket is writeable, or EOF */
+				occurred_events->events |= WL_SOCKET_WRITEABLE;
 			}
 
-	return result;
+			if (occurred_events->events != 0)
+			{
+				occurred_events->fd = cur_event->fd;
+				occurred_events++;
+				returned_events++;
+			}
+		}
+	}
+	return returned_events;
 }
-#endif   /* LATCH_USE_WIN32 */
+
+#elif defined(WAIT_USE_WIN32)
 
 /*
- * Sets a latch and wakes up anyone waiting on it.
- *
- * This is cheap if the latch is already set, otherwise not so much.
+ * Wait using Windows' WaitForMultipleObjects().
  *
- * 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.
+ * 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".
  */
-void
-SetLatch(volatile Latch *latch)
+static inline int
+WaitEventSetWaitBlock(WaitEventSet *set, int cur_timeout,
+					  WaitEvent *occurred_events, int nevents)
 {
-#ifndef WIN32
-	pid_t		owner_pid;
-#else
-	HANDLE		handle;
-#endif
+	int			returned_events = 0;
+	DWORD		rc;
+	WaitEvent  *cur_event;
 
 	/*
-	 * The memory barrier has be 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.
+	 * Sleep.
+	 *
+	 * Need to wait for ->nevents + 1, because signal handle is in [0].
 	 */
-	pg_memory_barrier();
-
-	/* Quick exit if already set */
-	if (latch->is_set)
-		return;
-
-	latch->is_set = true;
+	rc = WaitForMultipleObjects(set->nevents + 1, set->handles, FALSE,
+								cur_timeout);
 
-#ifndef WIN32
+	/* Check return code */
+	if (rc == WAIT_FAILED)
+		elog(ERROR, "WaitForMultipleObjects() failed: error code %lu",
+			 GetLastError());
+	else if (rc == WAIT_TIMEOUT)
+	{
+		/* timeout exceeded */
+		return -1;
+	}
 
-	/*
-	 * 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 to wake up the select()
-	 * 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 (rc == WAIT_OBJECT_0)
 	{
-		if (waiting)
-			sendSelfPipeByte();
+		/* Service newly-arrived signals */
+		pgwin32_dispatch_queued_signals();
+		return 0;				/* retry */
 	}
-	else
-		kill(owner_pid, SIGUSR1);
-#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).
+	 * With an offset of one, due to the always present pgwin32_signal_event,
+	 * the handle offset directly corresponds to a wait event.
 	 */
-	handle = latch->event;
-	if (handle)
+	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)
 	{
-		SetEvent(handle);
+		if (!ResetEvent(set->latch->event))
+			elog(ERROR, "ResetEvent failed: error code %lu", GetLastError());
 
+		if (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)
+	{
 		/*
-		 * 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().
+		 * 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 (!PostmasterIsAlive())
+		{
+			occurred_events->fd = PGINVALID_SOCKET;
+			occurred_events->events = WL_POSTMASTER_DEATH;
+			occurred_events++;
+			returned_events++;
 		}
-#endif
+	}
+	else if (cur_event->events & (WL_SOCKET_READABLE | WL_SOCKET_WRITEABLE))
+	{
+		WSANETWORKEVENTS resEvents;
+		HANDLE		handle = set->handles[cur_event->pos + 1];
 
-}
+		Assert(cur_event->fd);
 
-/*
- * Clear the latch. Calling WaitLatch after this will sleep, unless
- * the latch is set again before the WaitLatch call.
- */
-void
-ResetLatch(volatile Latch *latch)
-{
-	/* Only the owner should reset the latch */
-	Assert(latch->owner_pid == MyProcPid);
+		occurred_events->fd = cur_event->fd;
 
-	latch->is_set = false;
+		ZeroMemory(&resEvents, sizeof(resEvents));
+		if (WSAEnumNetworkEvents(cur_event->fd, handle, &resEvents) != 0)
+			elog(ERROR, "failed to enumerate network events: error code %u",
+				 WSAGetLastError());
+		if ((cur_event->events & WL_SOCKET_READABLE) &&
+			(resEvents.lNetworkEvents & FD_READ))
+		{
+			/* data available in socket */
+			occurred_events->events |= WL_SOCKET_READABLE;
+		}
+		if ((cur_event->events & WL_SOCKET_WRITEABLE) &&
+			(resEvents.lNetworkEvents & FD_WRITE))
+		{
+			/* writeable */
+			occurred_events->events |= WL_SOCKET_WRITEABLE;
+		}
+		if (resEvents.lNetworkEvents & FD_CLOSE)
+		{
+			/* EOF */
+			if (cur_event->events & WL_SOCKET_READABLE)
+				occurred_events->events |= WL_SOCKET_READABLE;
+			if (cur_event->events & WL_SOCKET_WRITEABLE)
+				occurred_events->events |= WL_SOCKET_WRITEABLE;
+		}
 
-	/*
-	 * 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();
+		if (occurred_events->events != 0)
+		{
+			occurred_events++;
+			returned_events++;
+		}
+	}
+
+	return returned_events;
 }
+#endif
 
 /*
  * SetLatch uses SIGUSR1 to wake up the process waiting on the latch.

src/backend/utils/init/miscinit.c

@@ -33,6 +33,7 @@
 
 #include "access/htup_details.h"
 #include "catalog/pg_authid.h"
+#include "libpq/libpq.h"
 #include "mb/pg_wchar.h"
 #include "miscadmin.h"
 #include "postmaster/autovacuum.h"
@@ -247,6 +248,9 @@ SwitchToSharedLatch(void)
 
 	MyLatch = &MyProc->procLatch;
 
+	if (FeBeWaitSet)
+		ModifyWaitEvent(FeBeWaitSet, 1, WL_LATCH_SET, MyLatch);
+
 	/*
 	 * Set the shared latch as the local one might have been set. This
 	 * shouldn't normally be necessary as code is supposed to check the
@@ -262,6 +266,10 @@ SwitchBackToLocalLatch(void)
 	Assert(MyProc != NULL && MyLatch == &MyProc->procLatch);
 
 	MyLatch = &LocalLatchData;
+
+	if (FeBeWaitSet)
+		ModifyWaitEvent(FeBeWaitSet, 1, WL_LATCH_SET, MyLatch);
+
 	SetLatch(MyLatch);
 }
 

src/include/libpq/libpq.h

@@ -19,6 +19,7 @@
 
 #include "lib/stringinfo.h"
 #include "libpq/libpq-be.h"
+#include "storage/latch.h"
 
 
 typedef struct
@@ -95,6 +96,8 @@ extern ssize_t secure_raw_write(Port *port, const void *ptr, size_t len);
 
 extern bool ssl_loaded_verify_locations;
 
+WaitEventSet *FeBeWaitSet;
+
 /* GUCs */
 extern char *SSLCipherSuites;
 extern char *SSLECDHCurve;

src/include/pg_config.h.in

@@ -530,6 +530,9 @@
 /* Define to 1 if you have the syslog interface. */
 #undef HAVE_SYSLOG
 
+/* Define to 1 if you have the <sys/epoll.h> header file. */
+#undef HAVE_SYS_EPOLL_H
+
 /* Define to 1 if you have the <sys/ioctl.h> header file. */
 #undef HAVE_SYS_IOCTL_H
 

src/include/storage/latch.h

@@ -68,6 +68,12 @@
  * use of any generic handler.
  *
  *
+ * WaitEventSets allow to wait for latches being set and additional events -
+ * postmaster dying and socket readiness of several sockets currently - at the
+ * same time.  On many platforms using a long lived event set is more
+ * efficient than using WaitLatch or WaitLatchOrSocket.
+ *
+ *
  * Portions Copyright (c) 1996-2016, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
@@ -95,13 +101,27 @@ typedef struct Latch
 #endif
 } Latch;
 
-/* Bitmasks for events that may wake-up WaitLatch() clients */
+/*
+ * Bitmasks for events that may wake-up WaitLatch(), WaitLatchOrSocket(), or
+ * WaitEventSetWait().
+ */
 #define WL_LATCH_SET		 (1 << 0)
 #define WL_SOCKET_READABLE	 (1 << 1)
 #define WL_SOCKET_WRITEABLE  (1 << 2)
-#define WL_TIMEOUT			 (1 << 3)
+#define WL_TIMEOUT			 (1 << 3)	/* not for WaitEventSetWait() */
 #define WL_POSTMASTER_DEATH  (1 << 4)
 
+typedef struct WaitEvent
+{
+	int			pos;			/* position in the event data structure */
+	uint32		events;			/* triggered events */
+	pgsocket	fd;				/* socket fd associated with event */
+	void	   *user_data;		/* pointer provided in AddWaitEventToSet */
+} WaitEvent;
+
+/* forward declaration to avoid exposing latch.c implementation details */
+typedef struct WaitEventSet WaitEventSet;
+
 /*
  * prototypes for functions in latch.c
  */
@@ -110,12 +130,19 @@ extern void InitLatch(volatile Latch *latch);
 extern void InitSharedLatch(volatile Latch *latch);
 extern void OwnLatch(volatile Latch *latch);
 extern void DisownLatch(volatile Latch *latch);
-extern int	WaitLatch(volatile Latch *latch, int wakeEvents, long timeout);
-extern int WaitLatchOrSocket(volatile Latch *latch, int wakeEvents,
-				  pgsocket sock, long timeout);
 extern void SetLatch(volatile Latch *latch);
 extern void ResetLatch(volatile Latch *latch);
 
+extern WaitEventSet *CreateWaitEventSet(MemoryContext context, int nevents);
+extern void FreeWaitEventSet(WaitEventSet *set);
+extern int AddWaitEventToSet(WaitEventSet *set, uint32 events, pgsocket fd,
+				  Latch *latch, void *user_data);
+extern void ModifyWaitEvent(WaitEventSet *set, int pos, uint32 events, Latch *latch);
+
+extern int	WaitEventSetWait(WaitEventSet *set, long timeout, WaitEvent *occurred_events, int nevents);
+extern int	WaitLatch(volatile Latch *latch, int wakeEvents, long timeout);
+extern int WaitLatchOrSocket(volatile Latch *latch, int wakeEvents,
+				  pgsocket sock, long timeout);
 
 /*
  * Unix implementation uses SIGUSR1 for inter-process signaling.

src/tools/pgindent/typedefs.list

@@ -2113,6 +2113,8 @@ WalSnd
 WalSndCtlData
 WalSndSendDataCallback
 WalSndState
+WaitEvent
+WaitEventSet
 WholeRowVarExprState
 WindowAgg
 WindowAggState