/*
* Like WaitLatch, but with an extra socket argument for WL_SOCKET_*
* conditions.
*
* When waiting on a socket, WL_SOCKET_READABLE *must* be included in
* 'wakeEvents'; WL_SOCKET_WRITEABLE is optional. The reason for this is
* that EOF and error conditions are reported only via WL_SOCKET_READABLE.
*/
int
WaitLatchOrSocket(volatile Latch *latch, int wakeEvents, pgsocket sock,
long timeout)
{
int result = 0;
int rc;
instr_time start_time,
cur_time;
long cur_timeout;
#ifdef HAVE_POLL
struct pollfd pfds[3];
int nfds;
#else
struct timeval tv,
*tvp;
fd_set input_mask;
fd_set output_mask;
int hifd;
#endif
/* Ignore WL_SOCKET_* events if no valid socket is given */
if (sock == PGINVALID_SOCKET)
wakeEvents &= ~(WL_SOCKET_READABLE | WL_SOCKET_WRITEABLE);
Assert(wakeEvents != 0); /* must have at least one wake event */
/* Cannot specify WL_SOCKET_WRITEABLE without WL_SOCKET_READABLE */
Assert((wakeEvents & (WL_SOCKET_READABLE | WL_SOCKET_WRITEABLE)) != WL_SOCKET_WRITEABLE);
if ((wakeEvents & WL_LATCH_SET) && latch->owner_pid != MyProcPid)
elog(ERROR, "cannot wait on a latch owned by another process");
/*
* Initialize timeout if requested. We must record the current time so
* that we can determine the remaining timeout if the poll() or select()
* is interrupted. (On some platforms, select() will update the contents
* of "tv" for us, but unfortunately we can't rely on that.)
*/
if (wakeEvents & WL_TIMEOUT)
{
INSTR_TIME_SET_CURRENT(start_time);
Assert(timeout >= 0 && timeout <= INT_MAX);
cur_timeout = timeout;
#ifndef HAVE_POLL
tv.tv_sec = cur_timeout / 1000L;
tv.tv_usec = (cur_timeout % 1000L) * 1000L;
tvp = &tv;
#endif
}
else
{
cur_timeout = -1;
#ifndef HAVE_POLL
tvp = NULL;
#endif
}
waiting = true;
do
{
/*
* Clear the pipe, then check if the latch is set already. If someone
* sets the latch between this and the poll()/select() below, the
* setter will write a byte to the pipe (or signal us and the signal
* handler will do that), and the poll()/select() will return
* immediately.
*
* Note: we assume that the kernel calls involved in drainSelfPipe()
* and SetLatch() will provide adequate synchronization on machines
* with weak memory ordering, so that we cannot miss seeing is_set if
* the signal byte is already in the pipe when we drain it.
*/
drainSelfPipe();
if ((wakeEvents & WL_LATCH_SET) && latch->is_set)
{
result |= WL_LATCH_SET;
/*
* Leave loop immediately, avoid blocking again. We don't attempt
* to report any other events that might also be satisfied.
*/
break;
}
/* Must wait ... we use poll(2) if available, otherwise select(2) */
#ifdef HAVE_POLL
nfds = 0;
if (wakeEvents & (WL_SOCKET_READABLE | WL_SOCKET_WRITEABLE))
{
/* socket, if used, is always in pfds[0] */
pfds[0].fd = sock;
pfds[0].events = 0;
if (wakeEvents & WL_SOCKET_READABLE)
pfds[0].events |= POLLIN;
if (wakeEvents & WL_SOCKET_WRITEABLE)
pfds[0].events |= POLLOUT;
pfds[0].revents = 0;
nfds++;
}
pfds[nfds].fd = selfpipe_readfd;
pfds[nfds].events = POLLIN;
pfds[nfds].revents = 0;
nfds++;
if (wakeEvents & WL_POSTMASTER_DEATH)
{
/* postmaster fd, if used, is always in pfds[nfds - 1] */
pfds[nfds].fd = postmaster_alive_fds[POSTMASTER_FD_WATCH];
pfds[nfds].events = POLLIN;
pfds[nfds].revents = 0;
nfds++;
}
/* Sleep */
rc = poll(pfds, nfds, (int) cur_timeout);
/* Check return code */
if (rc < 0)
{
/* EINTR is okay, otherwise complain */
if (errno != EINTR)
{
waiting = false;
ereport(ERROR,
(errcode_for_socket_access(),
errmsg("poll() failed: %m")));
}
}
else if (rc == 0)
{
/* timeout exceeded */
if (wakeEvents & WL_TIMEOUT)
result |= WL_TIMEOUT;
}
else
{
/* at least one event occurred, so check revents values */
if ((wakeEvents & WL_SOCKET_READABLE) &&
(pfds[0].revents & (POLLIN | POLLHUP | POLLERR | POLLNVAL)))
{
/* data available in socket, or EOF/error condition */
result |= WL_SOCKET_READABLE;
}
if ((wakeEvents & WL_SOCKET_WRITEABLE) &&
(pfds[0].revents & POLLOUT))
{
result |= WL_SOCKET_WRITEABLE;
}
/*
* We expect a POLLHUP when the remote end is closed, but because
* we don't expect the pipe to become readable or to have any
* errors either, treat those cases as postmaster death, too.
*/
if ((wakeEvents & WL_POSTMASTER_DEATH) &&
(pfds[nfds - 1].revents & (POLLHUP | POLLIN | POLLERR | POLLNVAL)))
{
/*
* According to the select(2) man page on Linux, select(2) may
* spuriously return and report a file descriptor as readable,
* when it's not; and presumably so can poll(2). It's not
* clear that the relevant cases would ever apply to the
* postmaster pipe, but since the consequences of falsely
* returning WL_POSTMASTER_DEATH could be pretty unpleasant,
* we take the trouble to positively verify EOF with
* PostmasterIsAlive().
*/
if (!PostmasterIsAlive())
result |= WL_POSTMASTER_DEATH;
}
}
#else /* !HAVE_POLL */
FD_ZERO(&input_mask);
FD_ZERO(&output_mask);
FD_SET(selfpipe_readfd, &input_mask);
hifd = selfpipe_readfd;
if (wakeEvents & WL_POSTMASTER_DEATH)
{
FD_SET(postmaster_alive_fds[POSTMASTER_FD_WATCH], &input_mask);
if (postmaster_alive_fds[POSTMASTER_FD_WATCH] > hifd)
hifd = postmaster_alive_fds[POSTMASTER_FD_WATCH];
}
if (wakeEvents & WL_SOCKET_READABLE)
{
FD_SET(sock, &input_mask);
if (sock > hifd)
hifd = sock;
}
if (wakeEvents & WL_SOCKET_WRITEABLE)
{
FD_SET(sock, &output_mask);
if (sock > hifd)
hifd = sock;
}
/* Sleep */
rc = select(hifd + 1, &input_mask, &output_mask, NULL, tvp);
/* Check return code */
if (rc < 0)
{
/* EINTR is okay, otherwise complain */
if (errno != EINTR)
{
waiting = false;
ereport(ERROR,
(errcode_for_socket_access(),
errmsg("select() failed: %m")));
}
}
else if (rc == 0)
{
/* timeout exceeded */
if (wakeEvents & WL_TIMEOUT)
result |= WL_TIMEOUT;
}
else
{
/* at least one event occurred, so check masks */
if ((wakeEvents & WL_SOCKET_READABLE) && FD_ISSET(sock, &input_mask))
{
/* data available in socket, or EOF */
result |= WL_SOCKET_READABLE;
}
if ((wakeEvents & WL_SOCKET_WRITEABLE) && FD_ISSET(sock, &output_mask))
{
result |= WL_SOCKET_WRITEABLE;
}
if ((wakeEvents & WL_POSTMASTER_DEATH) &&
FD_ISSET(postmaster_alive_fds[POSTMASTER_FD_WATCH], &input_mask))
{
/*
* According to the select(2) man page on Linux, select(2) may
* spuriously return and report a file descriptor as readable,
* when it's not; and presumably so can poll(2). It's not
* clear that the relevant cases would ever apply to the
* postmaster pipe, but since the consequences of falsely
* returning WL_POSTMASTER_DEATH could be pretty unpleasant,
* we take the trouble to positively verify EOF with
* PostmasterIsAlive().
*/
if (!PostmasterIsAlive())
result |= WL_POSTMASTER_DEATH;
}
}
#endif /* HAVE_POLL */
/* If we're not done, update cur_timeout for next iteration */
if (result == 0 && cur_timeout >= 0)
{
INSTR_TIME_SET_CURRENT(cur_time);
INSTR_TIME_SUBTRACT(cur_time, start_time);
cur_timeout = timeout - (long) INSTR_TIME_GET_MILLISEC(cur_time);
if (cur_timeout < 0)
cur_timeout = 0;
#ifndef HAVE_POLL
tv.tv_sec = cur_timeout / 1000L;
tv.tv_usec = (cur_timeout % 1000L) * 1000L;
#endif
}
} while (result == 0);
waiting = false;
return result;
}
/*
* Wait using linux's epoll_wait(2).
*
* This is the preferrable wait method, as several readiness notifications are
* delivered, without having to iterate through all of set->events. The return
* epoll_event struct contain a pointer to our events, making association
* easy.
*/
static inline int
WaitEventSetWaitBlock(WaitEventSet *set, int cur_timeout,
WaitEvent *occurred_events, int nevents)
{
int returned_events = 0;
int rc;
WaitEvent *cur_event;
struct epoll_event *cur_epoll_event;
/* Sleep */
rc = epoll_wait(set->epoll_fd, set->epoll_ret_events,
nevents, cur_timeout);
/* Check return code */
if (rc < 0)
{
/* EINTR is okay, otherwise complain */
if (errno != EINTR)
{
waiting = false;
ereport(ERROR,
(errcode_for_socket_access(),
errmsg("epoll_wait() failed: %m")));
}
return 0;
}
else if (rc == 0)
{
/* timeout exceeded */
return -1;
}
/*
* At least one event occurred, iterate over the returned epoll events
* until they're either all processed, or we've returned all the events
* the caller desired.
*/
for (cur_epoll_event = set->epoll_ret_events;
cur_epoll_event < (set->epoll_ret_events + rc) &&
returned_events < nevents;
cur_epoll_event++)
{
/* epoll's data pointer is set to the associated WaitEvent */
cur_event = (WaitEvent *) cur_epoll_event->data.ptr;
occurred_events->pos = cur_event->pos;
occurred_events->user_data = cur_event->user_data;
occurred_events->events = 0;
if (cur_event->events == WL_LATCH_SET &&
cur_epoll_event->events & (EPOLLIN | EPOLLERR | EPOLLHUP))
{
/* There's data in the self-pipe, clear it. */
drainSelfPipe();
if (set->latch->is_set)
{
occurred_events->fd = PGINVALID_SOCKET;
occurred_events->events = WL_LATCH_SET;
occurred_events++;
returned_events++;
}
}
else if (cur_event->events == WL_POSTMASTER_DEATH &&
cur_epoll_event->events & (EPOLLIN | EPOLLERR | EPOLLHUP))
{
/*
* We expect an EPOLLHUP when the remote end is closed, but
* because we don't expect the pipe to become readable or to have
* any errors either, treat those cases as postmaster death, too.
*
* As explained in the WAIT_USE_SELECT implementation, select(2)
* may spuriously return. Be paranoid about that here too, a
* spurious WL_POSTMASTER_DEATH would be painful.
*/
if (!PostmasterIsAlive())
{
occurred_events->fd = PGINVALID_SOCKET;
occurred_events->events = WL_POSTMASTER_DEATH;
occurred_events++;
returned_events++;
}
}
else if (cur_event->events & (WL_SOCKET_READABLE | WL_SOCKET_WRITEABLE))
{
Assert(cur_event->fd != PGINVALID_SOCKET);
if ((cur_event->events & WL_SOCKET_READABLE) &&
(cur_epoll_event->events & (EPOLLIN | EPOLLERR | EPOLLHUP)))
{
/* data available in socket, or EOF */
occurred_events->events |= WL_SOCKET_READABLE;
}
if ((cur_event->events & WL_SOCKET_WRITEABLE) &&
(cur_epoll_event->events & (EPOLLOUT | EPOLLERR | EPOLLHUP)))
{
/* writable, or EOF */
occurred_events->events |= WL_SOCKET_WRITEABLE;
}
if (occurred_events->events != 0)
{
occurred_events->fd = cur_event->fd;
occurred_events++;
returned_events++;
}
}
}
return returned_events;
}
/*
* Wait using poll(2).
*
* This allows to receive readiness notifications for several events at once,
* but requires iterating through all of set->pollfds.
*/
static inline int
WaitEventSetWaitBlock(WaitEventSet *set, int cur_timeout,
WaitEvent *occurred_events, int nevents)
{
int returned_events = 0;
int rc;
WaitEvent *cur_event;
struct pollfd *cur_pollfd;
/* Sleep */
rc = poll(set->pollfds, set->nevents, (int) cur_timeout);
/* Check return code */
if (rc < 0)
{
/* EINTR is okay, otherwise complain */
if (errno != EINTR)
{
waiting = false;
ereport(ERROR,
(errcode_for_socket_access(),
errmsg("poll() failed: %m")));
}
return 0;
}
else if (rc == 0)
{
/* timeout exceeded */
return -1;
}
for (cur_event = set->events, cur_pollfd = set->pollfds;
cur_event < (set->events + set->nevents) &&
returned_events < nevents;
cur_event++, cur_pollfd++)
{
/* no activity on this FD, skip */
if (cur_pollfd->revents == 0)
continue;
occurred_events->pos = cur_event->pos;
occurred_events->user_data = cur_event->user_data;
occurred_events->events = 0;
if (cur_event->events == WL_LATCH_SET &&
(cur_pollfd->revents & (POLLIN | POLLHUP | POLLERR | POLLNVAL)))
{
/* There's data in the self-pipe, clear it. */
drainSelfPipe();
if (set->latch->is_set)
{
occurred_events->fd = PGINVALID_SOCKET;
occurred_events->events = WL_LATCH_SET;
occurred_events++;
returned_events++;
}
}
else if (cur_event->events == WL_POSTMASTER_DEATH &&
(cur_pollfd->revents & (POLLIN | POLLHUP | POLLERR | POLLNVAL)))
{
/*
* We expect an POLLHUP when the remote end is closed, but because
* we don't expect the pipe to become readable or to have any
* errors either, treat those cases as postmaster death, too.
*
* As explained in the WAIT_USE_SELECT implementation, select(2)
* may spuriously return. Be paranoid about that here too, a
* spurious WL_POSTMASTER_DEATH would be painful.
*/
if (!PostmasterIsAlive())
{
occurred_events->fd = PGINVALID_SOCKET;
occurred_events->events = WL_POSTMASTER_DEATH;
occurred_events++;
returned_events++;
}
}
else if (cur_event->events & (WL_SOCKET_READABLE | WL_SOCKET_WRITEABLE))
{
int errflags = POLLHUP | POLLERR | POLLNVAL;
Assert(cur_event->fd >= PGINVALID_SOCKET);
if ((cur_event->events & WL_SOCKET_READABLE) &&
(cur_pollfd->revents & (POLLIN | errflags)))
{
/* data available in socket, or EOF */
occurred_events->events |= WL_SOCKET_READABLE;
}
if ((cur_event->events & WL_SOCKET_WRITEABLE) &&
(cur_pollfd->revents & (POLLOUT | errflags)))
{
/* writeable, or EOF */
occurred_events->events |= WL_SOCKET_WRITEABLE;
}
if (occurred_events->events != 0)
{
occurred_events->fd = cur_event->fd;
occurred_events++;
returned_events++;
}
}
}
return returned_events;
}
/*
* Wait using select(2).
*
* XXX: On at least older linux kernels select(), in violation of POSIX,
* doesn't reliably return a socket as writable if closed - but we rely on
* that. So far all the known cases of this problem are on platforms that also
* provide a poll() implementation without that bug. If we find one where
* that's not the case, we'll need to add a workaround.
*/
static inline int
WaitEventSetWaitBlock(WaitEventSet *set, int cur_timeout,
WaitEvent *occurred_events, int nevents)
{
int returned_events = 0;
int rc;
WaitEvent *cur_event;
fd_set input_mask;
fd_set output_mask;
int hifd;
struct timeval tv;
struct timeval *tvp = NULL;
FD_ZERO(&input_mask);
FD_ZERO(&output_mask);
/*
* Prepare input/output masks. We do so every loop iteration as there's no
* entirely portable way to copy fd_sets.
*/
for (cur_event = set->events;
cur_event < (set->events + set->nevents);
cur_event++)
{
if (cur_event->events == WL_LATCH_SET)
FD_SET(cur_event->fd, &input_mask);
else if (cur_event->events == WL_POSTMASTER_DEATH)
FD_SET(cur_event->fd, &input_mask);
else
{
Assert(cur_event->events & (WL_SOCKET_READABLE | WL_SOCKET_WRITEABLE));
if (cur_event->events == WL_SOCKET_READABLE)
FD_SET(cur_event->fd, &input_mask);
else if (cur_event->events == WL_SOCKET_WRITEABLE)
FD_SET(cur_event->fd, &output_mask);
}
if (cur_event->fd > hifd)
hifd = cur_event->fd;
}
/* Sleep */
if (cur_timeout >= 0)
{
tv.tv_sec = cur_timeout / 1000L;
tv.tv_usec = (cur_timeout % 1000L) * 1000L;
tvp = &tv;
}
rc = select(hifd + 1, &input_mask, &output_mask, NULL, tvp);
/* Check return code */
if (rc < 0)
{
/* EINTR is okay, otherwise complain */
if (errno != EINTR)
{
waiting = false;
ereport(ERROR,
(errcode_for_socket_access(),
errmsg("select() failed: %m")));
}
return 0; /* retry */
}
else if (rc == 0)
{
/* timeout exceeded */
return -1;
}
/*
* To associate events with select's masks, we have to check the status of
* the file descriptors associated with an event; by looping through all
* events.
*/
for (cur_event = set->events;
cur_event < (set->events + set->nevents)
&& returned_events < nevents;
cur_event++)
{
occurred_events->pos = cur_event->pos;
occurred_events->user_data = cur_event->user_data;
occurred_events->events = 0;
if (cur_event->events == WL_LATCH_SET &&
FD_ISSET(cur_event->fd, &input_mask))
{
/* There's data in the self-pipe, clear it. */
drainSelfPipe();
if (set->latch->is_set)
{
occurred_events->fd = PGINVALID_SOCKET;
occurred_events->events = WL_LATCH_SET;
occurred_events++;
returned_events++;
}
}
else if (cur_event->events == WL_POSTMASTER_DEATH &&
FD_ISSET(cur_event->fd, &input_mask))
{
/*
* According to the select(2) man page on Linux, select(2) may
* spuriously return and report a file descriptor as readable,
* when it's not; and presumably so can poll(2). It's not clear
* that the relevant cases would ever apply to the postmaster
* pipe, but since the consequences of falsely returning
* WL_POSTMASTER_DEATH could be pretty unpleasant, we take the
* trouble to positively verify EOF with PostmasterIsAlive().
*/
if (!PostmasterIsAlive())
{
occurred_events->fd = PGINVALID_SOCKET;
occurred_events->events = WL_POSTMASTER_DEATH;
occurred_events++;
returned_events++;
}
}
else if (cur_event->events & (WL_SOCKET_READABLE | WL_SOCKET_WRITEABLE))
{
Assert(cur_event->fd != PGINVALID_SOCKET);
if ((cur_event->events & WL_SOCKET_READABLE) &&
FD_ISSET(cur_event->fd, &input_mask))
{
/* data available in socket, or EOF */
occurred_events->events |= WL_SOCKET_READABLE;
}
if ((cur_event->events & WL_SOCKET_WRITEABLE) &&
FD_ISSET(cur_event->fd, &output_mask))
{
/* socket is writeable, or EOF */
occurred_events->events |= WL_SOCKET_WRITEABLE;
}
if (occurred_events->events != 0)
{
occurred_events->fd = cur_event->fd;
occurred_events++;
returned_events++;
}
}
}
return returned_events;
}
/*
* Like WaitLatch, but will also return when there's data available in
* 'sock' for reading. Returns 0 if timeout was reached, 1 if the latch
* was set, or 2 if the scoket became readable.
*/
int
WaitLatchOrSocket(volatile Latch *latch, pgsocket sock, long timeout)
{
struct timeval tv, *tvp = NULL;
fd_set input_mask;
int rc;
int result = 0;
if (latch->owner_pid != MyProcPid)
elog(ERROR, "cannot wait on a latch owned by another process");
/* Initialize timeout */
if (timeout >= 0)
{
tv.tv_sec = timeout / 1000000L;
tv.tv_usec = timeout % 1000000L;
tvp = &tv;
}
waiting = true;
for (;;)
{
int hifd;
/*
* Clear the pipe, and check if the latch is set already. If someone
* sets the latch between this and the select() below, the setter
* will write a byte to the pipe (or signal us and the signal handler
* will do that), and the select() will return immediately.
*/
drainSelfPipe();
if (latch->is_set)
{
result = 1;
break;
}
FD_ZERO(&input_mask);
FD_SET(selfpipe_readfd, &input_mask);
hifd = selfpipe_readfd;
if (sock != PGINVALID_SOCKET)
{
FD_SET(sock, &input_mask);
if (sock > hifd)
hifd = sock;
}
rc = select(hifd + 1, &input_mask, NULL, NULL, tvp);
if (rc < 0)
{
if (errno == EINTR)
continue;
ereport(ERROR,
(errcode_for_socket_access(),
errmsg("select() failed: %m")));
}
if (rc == 0)
{
/* timeout exceeded */
result = 0;
break;
}
if (sock != PGINVALID_SOCKET && FD_ISSET(sock, &input_mask))
{
result = 2;
break; /* data available in socket */
}
}
waiting = false;
return result;
}
