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/*-------------------------------------------------------------------------
*
* 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) 1996-2011, 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 <signal.h>
#include <unistd.h>
#include "miscadmin.h"
#include "storage/latch.h"
#include "storage/shmem.h"
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 %d", (int) 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 %d", (int) 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;
}
bool
WaitLatch(volatile Latch *latch, long timeout)
{
return WaitLatchOrSocket(latch, PGINVALID_SOCKET, false, false, timeout) > 0;
}
int
WaitLatchOrSocket(volatile Latch *latch, pgsocket sock, bool forRead,
bool forWrite, long timeout)
{
DWORD rc;
HANDLE events[3];
HANDLE latchevent;
HANDLE sockevent = WSA_INVALID_EVENT; /* silence compiler */
int numevents;
int result = 0;
if (latch->owner_pid != MyProcPid)
elog(ERROR, "cannot wait on a latch owned by another process");
latchevent = latch->event;
events[0] = latchevent;
events[1] = pgwin32_signal_event;
numevents = 2;
if (sock != PGINVALID_SOCKET && (forRead || forWrite))
{
int flags = 0;
if (forRead)
flags |= FD_READ;
if (forWrite)
flags |= FD_WRITE;
sockevent = WSACreateEvent();
WSAEventSelect(sock, sockevent, flags);
events[numevents++] = sockevent;
}
for (;;)
{
/*
* 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 %d", (int) GetLastError());
if (latch->is_set)
{
result = 1;
break;
}
rc = WaitForMultipleObjects(numevents, events, FALSE,
(timeout >= 0) ? timeout : INFINITE);
if (rc == WAIT_FAILED)
elog(ERROR, "WaitForMultipleObjects() failed: error code %d", (int) GetLastError());
else if (rc == WAIT_TIMEOUT)
{
result = 0;
break;
}
else if (rc == WAIT_OBJECT_0 + 1)
pgwin32_dispatch_queued_signals();
else if (rc == WAIT_OBJECT_0 + 2)
{
WSANETWORKEVENTS resEvents;
Assert(sock != PGINVALID_SOCKET);
ZeroMemory(&resEvents, sizeof(resEvents));
if (WSAEnumNetworkEvents(sock, sockevent, &resEvents) == SOCKET_ERROR)
ereport(FATAL,
(errmsg_internal("failed to enumerate network events: %i", (int) GetLastError())));
if ((forRead && resEvents.lNetworkEvents & FD_READ) ||
(forWrite && resEvents.lNetworkEvents & FD_WRITE))
result = 2;
break;
}
else if (rc != WAIT_OBJECT_0)
elog(ERROR, "unexpected return code from WaitForMultipleObjects(): %d", (int) rc);
}
/* Clean up the handle we created for the socket */
if (sock != PGINVALID_SOCKET && (forRead || forWrite))
{
WSAEventSelect(sock, sockevent, 0);
WSACloseEvent(sockevent);
}
return result;
}
void
SetLatch(volatile Latch *latch)
{
HANDLE handle;
/* 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;
}
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