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 limit on the range of FD numbers that can be accessed. The FD range limit does not appear to be a risk factor for any 9.1 usages, so this doesn't need to be back-patched, but we need to have it in place if we keep on expanding the uses of WaitLatch.
This commit is contained in:
Tom Lane
parent
d82d84864c
commit
a180776f7a
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@ -14,6 +14,9 @@
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* however reliably interrupts the sleep, and causes select() to return
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* immediately even if the signal arrives before select() begins.
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*
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* (Actually, we prefer poll() over select() where available, but the
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* same comments apply to it.)
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*
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* When SetLatch is called from the same process that owns the latch,
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* SetLatch writes the byte directly to the pipe. If it's owned by another
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* process, SIGUSR1 is sent and the signal handler in the waiting process
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@ -34,6 +37,12 @@
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#include <unistd.h>
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#include <sys/time.h>
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#include <sys/types.h>
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#ifdef HAVE_POLL_H
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#include <poll.h>
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#endif
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#ifdef HAVE_SYS_POLL_H
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#include <sys/poll.h>
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#endif
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#ifdef HAVE_SYS_SELECT_H
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#include <sys/select.h>
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#endif
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@ -175,12 +184,18 @@ int
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WaitLatchOrSocket(volatile Latch *latch, int wakeEvents, pgsocket sock,
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long timeout)
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{
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int result = 0;
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int rc;
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#ifdef HAVE_POLL
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struct pollfd pfds[3];
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int nfds;
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#else
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struct timeval tv,
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*tvp = NULL;
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fd_set input_mask;
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fd_set output_mask;
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int rc;
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int result = 0;
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int hifd;
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#endif
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/* Ignore WL_SOCKET_* events if no valid socket is given */
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if (sock == PGINVALID_SOCKET)
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@ -195,21 +210,29 @@ WaitLatchOrSocket(volatile Latch *latch, int wakeEvents, pgsocket sock,
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if (wakeEvents & WL_TIMEOUT)
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{
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Assert(timeout >= 0);
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#ifndef HAVE_POLL
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tv.tv_sec = timeout / 1000L;
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tv.tv_usec = (timeout % 1000L) * 1000L;
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tvp = &tv;
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#endif
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}
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else
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{
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#ifdef HAVE_POLL
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/* make sure poll() agrees there is no timeout */
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timeout = -1;
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#endif
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}
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waiting = true;
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do
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{
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int hifd;
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/*
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* Clear the pipe, then check if the latch is set already. If someone
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* sets the latch between this and the select() below, the setter will
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* write a byte to the pipe (or signal us and the signal handler will
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* do that), and the select() will return immediately.
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* sets the latch between this and the poll()/select() below, the
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* setter will write a byte to the pipe (or signal us and the signal
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* handler will do that), and the poll()/select() will return
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* immediately.
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*
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* Note: we assume that the kernel calls involved in drainSelfPipe()
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* and SetLatch() will provide adequate synchronization on machines
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@ -228,7 +251,73 @@ WaitLatchOrSocket(volatile Latch *latch, int wakeEvents, pgsocket sock,
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break;
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}
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/* Must wait ... set up the event masks for select() */
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/* Must wait ... we use poll(2) if available, otherwise select(2) */
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#ifdef HAVE_POLL
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nfds = 0;
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if (wakeEvents & (WL_SOCKET_READABLE | WL_SOCKET_WRITEABLE))
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{
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/* socket, if used, is always in pfds[0] */
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pfds[0].fd = sock;
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pfds[0].events = 0;
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if (wakeEvents & WL_SOCKET_READABLE)
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pfds[0].events |= POLLIN;
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if (wakeEvents & WL_SOCKET_WRITEABLE)
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pfds[0].events |= POLLOUT;
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pfds[0].revents = 0;
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nfds++;
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}
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pfds[nfds].fd = selfpipe_readfd;
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pfds[nfds].events = POLLIN;
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pfds[nfds].revents = 0;
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nfds++;
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if (wakeEvents & WL_POSTMASTER_DEATH)
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{
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/* postmaster fd, if used, is always in pfds[nfds - 1] */
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pfds[nfds].fd = postmaster_alive_fds[POSTMASTER_FD_WATCH];
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pfds[nfds].events = POLLIN;
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pfds[nfds].revents = 0;
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nfds++;
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}
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/* Sleep */
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rc = poll(pfds, nfds, (int) timeout);
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/* Check return code */
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if (rc < 0)
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{
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if (errno == EINTR)
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continue;
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waiting = false;
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ereport(ERROR,
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(errcode_for_socket_access(),
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errmsg("poll() failed: %m")));
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}
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if (rc == 0 && (wakeEvents & WL_TIMEOUT))
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{
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/* timeout exceeded */
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result |= WL_TIMEOUT;
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}
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if ((wakeEvents & WL_SOCKET_READABLE) &&
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(pfds[0].revents & POLLIN))
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{
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/* data available in socket */
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result |= WL_SOCKET_READABLE;
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}
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if ((wakeEvents & WL_SOCKET_WRITEABLE) &&
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(pfds[0].revents & POLLOUT))
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{
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result |= WL_SOCKET_WRITEABLE;
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}
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if ((wakeEvents & WL_POSTMASTER_DEATH) &&
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(pfds[nfds - 1].revents & POLLIN))
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{
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result |= WL_POSTMASTER_DEATH;
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}
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#else /* !HAVE_POLL */
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FD_ZERO(&input_mask);
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FD_ZERO(&output_mask);
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@ -288,6 +377,7 @@ WaitLatchOrSocket(volatile Latch *latch, int wakeEvents, pgsocket sock,
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{
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result |= WL_POSTMASTER_DEATH;
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}
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#endif /* HAVE_POLL */
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} while (result == 0);
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waiting = false;
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