/*-------------------------------------------------------------------------
 *
 * win32_latch.c
 *	  Routines for inter-process latches
 *
 * See unix_latch.c for header comments for the exported functions;
 * the API presented here is supposed to be the same as there.
 *
 * The Windows implementation uses Windows events that are inherited by
 * all postmaster child processes.
 *
 * Portions Copyright (c) 1996-2015, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * IDENTIFICATION
 *	  src/backend/port/win32_latch.c
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"

#include <fcntl.h>
#include <limits.h>
#include <signal.h>
#include <unistd.h>

#include "miscadmin.h"
#include "portability/instr_time.h"
#include "postmaster/postmaster.h"
#include "storage/barrier.h"
#include "storage/latch.h"
#include "storage/pmsignal.h"
#include "storage/shmem.h"


void
InitializeLatchSupport(void)
{
	/* currently, nothing to do here for Windows */
}

void
InitLatch(volatile Latch *latch)
{
	latch->is_set = false;
	latch->owner_pid = MyProcPid;
	latch->is_shared = false;

	latch->event = CreateEvent(NULL, TRUE, FALSE, NULL);
	if (latch->event == NULL)
		elog(ERROR, "CreateEvent failed: error code %lu", GetLastError());
}

void
InitSharedLatch(volatile Latch *latch)
{
	SECURITY_ATTRIBUTES sa;

	latch->is_set = false;
	latch->owner_pid = 0;
	latch->is_shared = true;

	/*
	 * 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());
}

void
OwnLatch(volatile Latch *latch)
{
	/* Sanity checks */
	Assert(latch->is_shared);
	if (latch->owner_pid != 0)
		elog(ERROR, "latch already owned");

	latch->owner_pid = MyProcPid;
}

void
DisownLatch(volatile Latch *latch)
{
	Assert(latch->is_shared);
	Assert(latch->owner_pid == MyProcPid);

	latch->owner_pid = 0;
}

int
WaitLatch(volatile Latch *latch, int wakeEvents, long timeout)
{
	return WaitLatchOrSocket(latch, wakeEvents, PGINVALID_SOCKET, timeout);
}

int
WaitLatchOrSocket(volatile Latch *latch, int wakeEvents, pgsocket sock,
				  long timeout)
{
	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;

	/* Ignore WL_SOCKET_* events if no valid socket is given */
	if (sock == PGINVALID_SOCKET)
		wakeEvents &= ~(WL_SOCKET_READABLE | WL_SOCKET_WRITEABLE);

	Assert(wakeEvents != 0);	/* must have at least one wake event */

	if ((wakeEvents & WL_LATCH_SET) && latch->owner_pid != MyProcPid)
		elog(ERROR, "cannot wait on a latch owned by another process");

	/*
	 * Initialize timeout if requested.  We must record the current time so
	 * that we can determine the remaining timeout if WaitForMultipleObjects
	 * is interrupted.
	 */
	if (wakeEvents & WL_TIMEOUT)
	{
		INSTR_TIME_SET_CURRENT(start_time);
		Assert(timeout >= 0 && timeout <= INT_MAX);
		cur_timeout = timeout;
	}
	else
		cur_timeout = INFINITE;

	/*
	 * Construct an array of event handles for WaitforMultipleObjects().
	 *
	 * 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.
	 */
	latchevent = latch->event;

	events[0] = pgwin32_signal_event;
	events[1] = latchevent;
	numevents = 2;
	if (wakeEvents & (WL_SOCKET_READABLE | WL_SOCKET_WRITEABLE))
	{
		/* Need an event object to represent events on the socket */
		int			flags = FD_CLOSE; /* always check for errors/EOF */

		if (wakeEvents & WL_SOCKET_READABLE)
			flags |= FD_READ;
		if (wakeEvents & WL_SOCKET_WRITEABLE)
			flags |= FD_WRITE;

		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());

		events[numevents++] = sockevent;
	}
	if (wakeEvents & WL_POSTMASTER_DEATH)
	{
		pmdeath_eventno = numevents;
		events[numevents++] = PostmasterHandle;
	}

	/* Ensure that signals are serviced even if latch is already set */
	pgwin32_dispatch_queued_signals();

	do
	{
		/*
		 * Reset the event, and check if the latch is set already. If someone
		 * sets the latch between this and the WaitForMultipleObjects() call
		 * below, the setter will set the event and WaitForMultipleObjects()
		 * will return immediately.
		 */
		if (!ResetEvent(latchevent))
			elog(ERROR, "ResetEvent failed: error code %lu", GetLastError());

		if ((wakeEvents & WL_LATCH_SET) && latch->is_set)
		{
			result |= WL_LATCH_SET;

			/*
			 * Leave loop immediately, avoid blocking again. We don't attempt
			 * to report any other events that might also be satisfied.
			 */
			break;
		}

		rc = WaitForMultipleObjects(numevents, events, FALSE, cur_timeout);

		if (rc == WAIT_FAILED)
			elog(ERROR, "WaitForMultipleObjects() failed: error code %lu",
				 GetLastError());
		else if (rc == WAIT_TIMEOUT)
		{
			result |= WL_TIMEOUT;
		}
		else if (rc == WAIT_OBJECT_0)
		{
			/* Service newly-arrived signals */
			pgwin32_dispatch_queued_signals();
		}
		else if (rc == WAIT_OBJECT_0 + 1)
		{
			/*
			 * Latch is set.  We'll handle that on next iteration of loop, but
			 * let's not waste the cycles to update cur_timeout below.
			 */
			continue;
		}
		else if ((wakeEvents & (WL_SOCKET_READABLE | WL_SOCKET_WRITEABLE)) &&
				 rc == WAIT_OBJECT_0 + 2)		/* socket is at event slot 2 */
		{
			WSANETWORKEVENTS resEvents;

			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))
			{
				result |= WL_SOCKET_READABLE;
			}
			if ((wakeEvents & WL_SOCKET_WRITEABLE) &&
				(resEvents.lNetworkEvents & FD_WRITE))
			{
				result |= WL_SOCKET_WRITEABLE;
			}
			if (resEvents.lNetworkEvents & FD_CLOSE)
			{
				if (wakeEvents & WL_SOCKET_READABLE)
					result |= WL_SOCKET_READABLE;
				if (wakeEvents & WL_SOCKET_WRITEABLE)
					result |= WL_SOCKET_WRITEABLE;
			}
		}
		else if ((wakeEvents & WL_POSTMASTER_DEATH) &&
				 rc == WAIT_OBJECT_0 + pmdeath_eventno)
		{
			/*
			 * 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())
				result |= WL_POSTMASTER_DEATH;
		}
		else
			elog(ERROR, "unexpected return code from WaitForMultipleObjects(): %lu", rc);

		/* If we're not done, update cur_timeout for next iteration */
		if (result == 0 && cur_timeout != INFINITE)
		{
			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)
				cur_timeout = 0;
		}
	} while (result == 0);

	/* Clean up the event object we created for the socket */
	if (sockevent != WSA_INVALID_EVENT)
	{
		WSAEventSelect(sock, NULL, 0);
		WSACloseEvent(sockevent);
	}

	return result;
}

/*
 * The comments above the unix implementation (unix_latch.c) of this function
 * apply here as well.
 */
void
SetLatch(volatile Latch *latch)
{
	HANDLE		handle;

	/*
	 * 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;

	/*
	 * 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().
		 */
	}
}

void
ResetLatch(volatile Latch *latch)
{
	/* Only the owner should reset the latch */
	Assert(latch->owner_pid == MyProcPid);

	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();
}
