8000 Improve Windows implementation of WaitLatch/WaitLatchOrSocket. · postgres/postgres@8ebc908 · GitHub
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Improve Windows implementation of WaitLatch/WaitLatchOrSocket.
Ensure that signal handlers are serviced before this function returns. This should make the behavior more like Unix. Also, add some more error checking, and make some other cosmetic improvements. No back-patch since it's not clear whether this is fixing any live bug that would affect 9.1. I'm more concerned about 9.2 anyway given our considerable recent expansions in the usage of WaitLatch.
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‎src/backend/port/win32_latch.c

Lines changed: 39 additions & 21 deletions
Original file line numberDiff line numberDiff line change
@@ -115,14 +115,19 @@ WaitLatchOrSocket(volatile Latch *latch, int wakeEvents, pgsocket sock,
115115
else
116116
timeout = INFINITE;
117117

118-
/* Construct an array of event handles for WaitforMultipleObjects() */
118+
/*
119+
* Construct an array of event handles for WaitforMultipleObjects().
120+
*
121+
* Note: pgwin32_signal_event should be first to ensure that it will be
122+
* reported when multiple events are set. We want to guarantee that
123+
* pending signals are serviced.
124+
*/
119125
latchevent = latch->event;
120126

121-
events[0] = latchevent;
122-
events[1] = pgwin32_signal_event;
127+
events[0] = pgwin32_signal_event;
128+
events[1] = latchevent;
123129
numevents = 2;
124-
if ((wakeEvents & WL_SOCKET_READABLE) ||
125-
(wakeEvents & WL_SOCKET_WRITEABLE))
130+
if (wakeEvents & (WL_SOCKET_READABLE | WL_SOCKET_WRITEABLE))
126131
{
127132
int flags = 0;
128133

@@ -132,7 +137,13 @@ WaitLatchOrSocket(volatile Latch *latch, int wakeEvents, pgsocket sock,
132137
flags |= FD_WRITE;
133138

134139
sockevent = WSACreateEvent();
135-
WSAEventSelect(sock, sockevent, flags);
140+
if (sockevent == WSA_INVALID_EVENT)
141+
elog(ERROR, "failed to create event for socket: error code %u",
142+
WSAGetLastError());
143+
if (WSAEventSelect(sock, sockevent, flags) != 0)
144+
elog(ERROR, "failed to set up event for socket: error code %u",
145+
WSAGetLastError());
146+
136147
events[numevents++] = sockevent;
137148
}
138149
if (wakeEvents & WL_POSTMASTER_DEATH)
@@ -141,6 +152,9 @@ WaitLatchOrSocket(volatile Latch *latch, int wakeEvents, pgsocket sock,
141152
events[numevents++] = PostmasterHandle;
142153
}
143154

155+
/* Ensure that signals are serviced even if latch is already set */
156+
pgwin32_dispatch_queued_signals();
157+
144158
do
145159
{
146160
/*
@@ -151,6 +165,7 @@ WaitLatchOrSocket(volatile Latch *latch, int wakeEvents, pgsocket sock,
151165
*/
152166
if (!ResetEvent(latchevent))
153167
elog(ERROR, "ResetEvent failed: error code %lu", GetLastError());
168+
154169
if ((wakeEvents & WL_LATCH_SET) && latch->is_set)
155170
{
156171
result |= WL_LATCH_SET;
@@ -164,21 +179,20 @@ WaitLatchOrSocket(volatile Latch *latch, int wakeEvents, pgsocket sock,
164179
rc = WaitForMultipleObjects(numevents, events, FALSE, timeout);
165180

166181
if (rc == WAIT_FAILED)
167-
elog(ERROR, "WaitForMultipleObjects() failed: error code %lu", GetLastError());
168-
169-
/* Participate in Windows signal emulation */
170-
else if (rc == WAIT_OBJECT_0 + 1)
171-
pgwin32_dispatch_queued_signals();
172-
182+
elog(ERROR, "WaitForMultipleObjects() failed: error code %lu",
183+
GetLastError());
173184
else if (rc == WAIT_TIMEOUT)
174185
{
175186
result |= WL_TIMEOUT;
176187
}
177-
else if ((wakeEvents & WL_POSTMASTER_DEATH) &&
178-
rc == WAIT_OBJECT_0 + pmdeath_eventno)
188+
else if (rc == WAIT_OBJECT_0)
179189
{
180-
/* Postmaster died */
181-
result |= WL_POSTMASTER_DEATH;
190+
/* Service newly-arrived signals */
191+
pgwin32_dispatch_queued_signals();
192+
}
193+
else if (rc == WAIT_OBJECT_0 + 1)
194+
{
195+
/* Latch is set, we'll handle that on next iteration of loop */
182196
}
183197
else if ((wakeEvents & (WL_SOCKET_READABLE | WL_SOCKET_WRITEABLE)) &&
184198
rc == WAIT_OBJECT_0 + 2) /* socket is at event slot 2 */
@@ -187,9 +201,8 @@ WaitLatchOrSocket(volatile Latch *latch, int wakeEvents, pgsocket sock,
187201

188202
ZeroMemory(&resEvents, sizeof(resEvents));
189203
if (WSAEnumNetworkEvents(sock, sockevent, &resEvents) == SOCKET_ERROR)
190-
ereport(FATAL,
191-
(errmsg_internal("failed to enumerate network events: error code %lu", GetLastError())));
192-
204+
elog(ERROR, "failed to enumerate network events: error code %lu",
205+
GetLastError());
193206
if ((wakeEvents & WL_SOCKET_READABLE) &&
194207
(resEvents.lNetworkEvents & FD_READ))
195208
{
@@ -201,8 +214,13 @@ WaitLatchOrSocket(volatile Latch *latch, int wakeEvents, pgsocket sock,
201214
result |= WL_SOCKET_WRITEABLE;
202215
}
203216
}
204-
/* Otherwise it must be the latch event */
205-
else if (rc != WAIT_OBJECT_0)
217+
else if ((wakeEvents & WL_POSTMASTER_DEATH) &&
218+
rc == WAIT_OBJECT_0 + pmdeath_eventno)
219+
{
220+
/* Postmaster died */
221+
result |= WL_POSTMASTER_DEATH;
222+
}
223+
else
206224
elog(ERROR, "unexpected return code from WaitForMultipleObjects(): %lu", rc);
207225
}
208226
while (result == 0);

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