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Commita180776

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Teach unix_latch.c to use poll() where available.
poll() is preferred over select() on platforms where both are available,because it tends to be a bit faster and it doesn't have an arbitrary limiton the range of FD numbers that can be accessed. The FD range limit doesnot appear to be a risk factor for any 9.1 usages, so this doesn't need tobe back-patched, but we need to have it in place if we keep on expandingthe uses of WaitLatch.
1 parentd82d848 commita180776

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1 file changed

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-8
lines changed

1 file changed

+98
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‎src/backend/port/unix_latch.c

Lines changed: 98 additions & 8 deletions
Original file line numberDiff line numberDiff line change
@@ -14,6 +14,9 @@
1414
* however reliably interrupts the sleep, and causes select() to return
1515
* immediately even if the signal arrives before select() begins.
1616
*
17+
* (Actually, we prefer poll() over select() where available, but the
18+
* same comments apply to it.)
19+
*
1720
* When SetLatch is called from the same process that owns the latch,
1821
* SetLatch writes the byte directly to the pipe. If it's owned by another
1922
* process, SIGUSR1 is sent and the signal handler in the waiting process
@@ -34,6 +37,12 @@
3437
#include<unistd.h>
3538
#include<sys/time.h>
3639
#include<sys/types.h>
40+
#ifdefHAVE_POLL_H
41+
#include<poll.h>
42+
#endif
43+
#ifdefHAVE_SYS_POLL_H
44+
#include<sys/poll.h>
45+
#endif
3746
#ifdefHAVE_SYS_SELECT_H
3847
#include<sys/select.h>
3948
#endif
@@ -175,12 +184,18 @@ int
175184
WaitLatchOrSocket(volatileLatch*latch,intwakeEvents,pgsocketsock,
176185
longtimeout)
177186
{
187+
intresult=0;
188+
intrc;
189+
#ifdefHAVE_POLL
190+
structpollfdpfds[3];
191+
intnfds;
192+
#else
178193
structtimevaltv,
179194
*tvp=NULL;
180195
fd_setinput_mask;
181196
fd_setoutput_mask;
182-
intrc;
183-
intresult=0;
197+
inthifd;
198+
#endif
184199

185200
/* Ignore WL_SOCKET_* events if no valid socket is given */
186201
if (sock==PGINVALID_SOCKET)
@@ -195,21 +210,29 @@ WaitLatchOrSocket(volatile Latch *latch, int wakeEvents, pgsocket sock,
195210
if (wakeEvents&WL_TIMEOUT)
196211
{
197212
Assert(timeout >=0);
213+
#ifndefHAVE_POLL
198214
tv.tv_sec=timeout /1000L;
199215
tv.tv_usec= (timeout %1000L)*1000L;
200216
tvp=&tv;
217+
#endif
218+
}
219+
else
220+
{
221+
#ifdefHAVE_POLL
222+
/* make sure poll() agrees there is no timeout */
223+
timeout=-1;
224+
#endif
201225
}
202226

203227
waiting= true;
204228
do
205229
{
206-
inthifd;
207-
208230
/*
209231
* Clear the pipe, then check if the latch is set already. If someone
210-
* sets the latch between this and the select() below, the setter will
211-
* write a byte to the pipe (or signal us and the signal handler will
212-
* do that), and the select() will return immediately.
232+
* sets the latch between this and the poll()/select() below, the
233+
* setter will write a byte to the pipe (or signal us and the signal
234+
* handler will do that), and the poll()/select() will return
235+
* immediately.
213236
*
214237
* Note: we assume that the kernel calls involved in drainSelfPipe()
215238
* and SetLatch() will provide adequate synchronization on machines
@@ -228,7 +251,73 @@ WaitLatchOrSocket(volatile Latch *latch, int wakeEvents, pgsocket sock,
228251
break;
229252
}
230253

231-
/* Must wait ... set up the event masks for select() */
254+
/* Must wait ... we use poll(2) if available, otherwise select(2) */
255+
#ifdefHAVE_POLL
256+
nfds=0;
257+
if (wakeEvents& (WL_SOCKET_READABLE |WL_SOCKET_WRITEABLE))
258+
{
259+
/* socket, if used, is always in pfds[0] */
260+
pfds[0].fd=sock;
261+
pfds[0].events=0;
262+
if (wakeEvents&WL_SOCKET_READABLE)
263+
pfds[0].events |=POLLIN;
264+
if (wakeEvents&WL_SOCKET_WRITEABLE)
265+
pfds[0].events |=POLLOUT;
266+
pfds[0].revents=0;
267+
nfds++;
268+
}
269+
270+
pfds[nfds].fd=selfpipe_readfd;
271+
pfds[nfds].events=POLLIN;
272+
pfds[nfds].revents=0;
273+
nfds++;
274+
275+
if (wakeEvents&WL_POSTMASTER_DEATH)
276+
{
277+
/* postmaster fd, if used, is always in pfds[nfds - 1] */
278+
pfds[nfds].fd=postmaster_alive_fds[POSTMASTER_FD_WATCH];
279+
pfds[nfds].events=POLLIN;
280+
pfds[nfds].revents=0;
281+
nfds++;
282+
}
283+
284+
/* Sleep */
285+
rc=poll(pfds,nfds, (int)timeout);
286+
287+
/* Check return code */
288+
if (rc<0)
289+
{
290+
if (errno==EINTR)
291+
continue;
292+
waiting= false;
293+
ereport(ERROR,
294+
(errcode_for_socket_access(),
295+
errmsg("poll() failed: %m")));
296+
}
297+
if (rc==0&& (wakeEvents&WL_TIMEOUT))
298+
{
299+
/* timeout exceeded */
300+
result |=WL_TIMEOUT;
301+
}
302+
if ((wakeEvents&WL_SOCKET_READABLE)&&
303+
(pfds[0].revents&POLLIN))
304+
{
305+
/* data available in socket */
306+
result |=WL_SOCKET_READABLE;
307+
}
308+
if ((wakeEvents&WL_SOCKET_WRITEABLE)&&
309+
(pfds[0].revents&POLLOUT))
310+
{
311+
result |=WL_SOCKET_WRITEABLE;
312+
}
313+
if ((wakeEvents&WL_POSTMASTER_DEATH)&&
314+
(pfds[nfds-1].revents&POLLIN))
315+
{
316+
result |=WL_POSTMASTER_DEATH;
317+
}
318+
319+
#else/* !HAVE_POLL */
320+
232321
FD_ZERO(&input_mask);
233322
FD_ZERO(&output_mask);
234323

@@ -288,6 +377,7 @@ WaitLatchOrSocket(volatile Latch *latch, int wakeEvents, pgsocket sock,
288377
{
289378
result |=WL_POSTMASTER_DEATH;
290379
}
380+
#endif/* HAVE_POLL */
291381
}while (result==0);
292382
waiting= false;
293383

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