* In the postmaster, we want to install non-ignored handlers *without*
* SA_RESTART. This is because they'll be blocked at all times except
* when ServerLoop is waiting for something to happen, and during that
- * window, we want signals to exit the select(2) wait so that ServerLoop
+ * window, we want signals to exit the pselect(2) wait so that ServerLoop
* can respond if anything interesting happened. On some platforms,
- * signals marked SA_RESTART would not cause the select() wait to end.
+ * signals marked SA_RESTART would not cause the pselect() wait to end.
* Child processes will generally want SA_RESTART, but we expect them to
* set up their own handlers before unblocking signals.
*
for (;;)
{
fd_set rmask;
+ fd_set *rmask_p;
+ struct timeval timeout;
int selres;
time_t now;
* We block all signals except while sleeping. That makes it safe for
* signal handlers, which again block all signals while executing, to
* do nontrivial work.
- *
- * If we are in PM_WAIT_DEAD_END state, then we don't want to accept
- * any new connections, so we don't call select(), and just sleep.
*/
- memcpy((char *) &rmask, (char *) &readmask, sizeof(fd_set));
-
if (pmState == PM_WAIT_DEAD_END)
{
- PG_SETMASK(&UnBlockSig);
-
- pg_usleep(100000L); /* 100 msec seems reasonable */
- selres = 0;
-
- PG_SETMASK(&BlockSig);
+ /*
+ * If we are in PM_WAIT_DEAD_END state, then we don't want to
+ * accept any new connections, so pass a null rmask.
+ */
+ rmask_p = NULL;
+ timeout.tv_sec = 0;
+ timeout.tv_usec = 100000; /* 100 msec seems reasonable */
}
else
{
- /* must set timeout each time; some OSes change it! */
- struct timeval timeout;
+ /* Normal case: check sockets, and compute a suitable timeout */
+ memcpy(&rmask, &readmask, sizeof(fd_set));
+ rmask_p = &rmask;
/* Needs to run with blocked signals! */
DetermineSleepTime(&timeout);
+ }
+ /*
+ * We prefer to wait with pselect(2) if available, as using that,
+ * together with *not* using SA_RESTART for signals, guarantees that
+ * we will get kicked off the wait if a signal occurs.
+ *
+ * If we lack pselect(2), fake it with select(2). This has a race
+ * condition: a signal that was already pending will be delivered
+ * before we reach the select(), and therefore the select() will wait,
+ * even though we might wish to do something in response. Therefore,
+ * beware of putting any time-critical signal response logic into
+ * ServerLoop rather than into the signal handler itself. It will run
+ * eventually, but maybe not till after a timeout delay.
+ *
+ * Some implementations of pselect() are reportedly not atomic, making
+ * the first alternative here functionally equivalent to the second.
+ * Not much we can do about that though.
+ */
+ {
+#ifdef HAVE_PSELECT
+ /* pselect uses a randomly different timeout API, sigh */
+ struct timespec ptimeout;
+
+ ptimeout.tv_sec = timeout.tv_sec;
+ ptimeout.tv_nsec = timeout.tv_usec * 1000;
+
+ selres = pselect(nSockets, rmask_p, NULL, NULL,
+ &ptimeout, &UnBlockSig);
+#else
PG_SETMASK(&UnBlockSig);
- selres = select(nSockets, &rmask, NULL, NULL, &timeout);
+ selres = select(nSockets, rmask_p, NULL, NULL, &timeout);
PG_SETMASK(&BlockSig);
+#endif
}
- /* Now check the select() result */
+ /* Now check the select()/pselect() result */
if (selres < 0)
{
if (errno != EINTR && errno != EWOULDBLOCK)
projects / postgresql / commitdiff