#include "include.h" #if PG_VERSION_NUM < 90600 /*------------------------------------------------------------------------- * * latch.c * Routines for inter-process latches * * The Unix implementation uses the so-called self-pipe trick to overcome the * race condition involved with poll() (or epoll_wait() on linux) and setting * a global flag in the signal handler. When a latch is set and the current * process is waiting for it, the signal handler wakes up the poll() in * WaitLatch by writing a byte to a pipe. A signal by itself doesn't interrupt * poll() on all platforms, and even on platforms where it does, a signal that * arrives just before the poll() call does not prevent poll() from entering * sleep. An incoming byte on a pipe however reliably interrupts the sleep, * and causes poll() to return immediately even if the signal arrives before * poll() begins. * * When SetLatch is called from the same process that owns the latch, * SetLatch writes the byte directly to the pipe. If it's owned by another * process, SIGUSR1 is sent and the signal handler in the waiting process * writes the byte to the pipe on behalf of the signaling process. * * The Windows implementation uses Windows events that are inherited by all * postmaster child processes. There's no need for the self-pipe trick there. * * Portions Copyright (c) 1996-2017, PostgreSQL Global Development Group * Portions Copyright (c) 1994, Regents of the University of California * * IDENTIFICATION * src/backend/storage/ipc/latch.c * *------------------------------------------------------------------------- */ #include "postgres.h" #include #include #include #include #ifdef HAVE_SYS_EPOLL_H #include #endif #ifdef HAVE_POLL_H #include #endif #include "miscadmin.h" #include "pgstat.h" #include "portability/instr_time.h" #include "postmaster/postmaster.h" #include "storage/latch.h" #include "storage/pmsignal.h" #include "storage/shmem.h" /* * Select the fd readiness primitive to use. Normally the "most modern" * primitive supported by the OS will be used, but for testing it can be * useful to manually specify the used primitive. If desired, just add a * define somewhere before this block. */ #if defined(WAIT_USE_EPOLL) || defined(WAIT_USE_POLL) || \ defined(WAIT_USE_WIN32) /* don't overwrite manual choice */ #elif defined(HAVE_SYS_EPOLL_H) #define WAIT_USE_EPOLL #elif defined(HAVE_POLL) #define WAIT_USE_POLL #elif WIN32 #define WAIT_USE_WIN32 #else #error "no wait set implementation available" #endif /* typedef in latch.h */ struct WaitEventSet { int nevents; /* number of registered events */ int nevents_space; /* maximum number of events in this set */ /* * Array, of nevents_space length, storing the definition of events this * set is waiting for. */ WaitEvent *events; /* * If WL_LATCH_SET is specified in any wait event, latch is a pointer to * said latch, and latch_pos the offset in the ->events array. This is * useful because we check the state of the latch before performing doing * syscalls related to waiting. */ Latch *latch; int latch_pos; #if defined(WAIT_USE_EPOLL) int epoll_fd; /* epoll_wait returns events in a user provided arrays, allocate once */ struct epoll_event *epoll_ret_events; #elif defined(WAIT_USE_POLL) /* poll expects events to be waited on every poll() call, prepare once */ struct pollfd *pollfds; #elif defined(WAIT_USE_WIN32) /* * Array of windows events. The first element always contains * pgwin32_signal_event, so the remaining elements are offset by one (i.e. * event->pos + 1). */ HANDLE *handles; #endif }; #ifndef WIN32 /* Are we currently in WaitLatch? The signal handler would like to know. */ static volatile sig_atomic_t waiting = false; /* Read and write ends of the self-pipe */ static int selfpipe_readfd = -1; /* Private function prototypes */ static void drainSelfPipe(void); #endif /* WIN32 */ #if defined(WAIT_USE_EPOLL) static void WaitEventAdjustEpoll(WaitEventSet *set, WaitEvent *event, int action); #elif defined(WAIT_USE_POLL) static void WaitEventAdjustPoll(WaitEventSet *set, WaitEvent *event); #elif defined(WAIT_USE_WIN32) static void WaitEventAdjustWin32(WaitEventSet *set, WaitEvent *event); #endif static inline int WaitEventSetWaitBlock(WaitEventSet *set, int cur_timeout, WaitEvent *occurred_events, int nevents); /* * Create a WaitEventSet with space for nevents different events to wait for. * * These events can then be efficiently waited upon together, using * WaitEventSetWait(). */ WaitEventSet * CreateWaitEventSet(MemoryContext context, int nevents) { WaitEventSet *set; char *data; Size sz = 0; /* * Use MAXALIGN size/alignment to guarantee that later uses of memory are * aligned correctly. E.g. epoll_event might need 8 byte alignment on some * platforms, but earlier allocations like WaitEventSet and WaitEvent * might not sized to guarantee that when purely using sizeof(). */ sz += MAXALIGN(sizeof(WaitEventSet)); sz += MAXALIGN(sizeof(WaitEvent) * nevents); #if defined(WAIT_USE_EPOLL) sz += MAXALIGN(sizeof(struct epoll_event) * nevents); #elif defined(WAIT_USE_POLL) sz += MAXALIGN(sizeof(struct pollfd) * nevents); #elif defined(WAIT_USE_WIN32) /* need space for the pgwin32_signal_event */ sz += MAXALIGN(sizeof(HANDLE) * (nevents + 1)); #endif data = (char *) MemoryContextAllocZero(context, sz); set = (WaitEventSet *) data; data += MAXALIGN(sizeof(WaitEventSet)); set->events = (WaitEvent *) data; data += MAXALIGN(sizeof(WaitEvent) * nevents); #if defined(WAIT_USE_EPOLL) set->epoll_ret_events = (struct epoll_event *) data; data += MAXALIGN(sizeof(struct epoll_event) * nevents); #elif defined(WAIT_USE_POLL) set->pollfds = (struct pollfd *) data; data += MAXALIGN(sizeof(struct pollfd) * nevents); #elif defined(WAIT_USE_WIN32) set->handles = (HANDLE) data; data += MAXALIGN(sizeof(HANDLE) * nevents); #endif set->latch = NULL; set->nevents_space = nevents; #if defined(WAIT_USE_EPOLL) #ifdef EPOLL_CLOEXEC set->epoll_fd = epoll_create1(EPOLL_CLOEXEC); if (set->epoll_fd < 0) elog(ERROR, "epoll_create1 failed: %m"); #else /* cope with ancient glibc lacking epoll_create1 (e.g., RHEL5) */ set->epoll_fd = epoll_create(nevents); if (set->epoll_fd < 0) elog(ERROR, "epoll_create failed: %m"); if (fcntl(set->epoll_fd, F_SETFD, FD_CLOEXEC) == -1) elog(ERROR, "fcntl(F_SETFD) failed on epoll descriptor: %m"); #endif /* EPOLL_CLOEXEC */ #elif defined(WAIT_USE_WIN32) /* * To handle signals while waiting, we need to add a win32 specific event. * We accounted for the additional event at the top of this routine. See * port/win32/signal.c for more details. * * Note: pgwin32_signal_event should be first to ensure that it will be * reported when multiple events are set. We want to guarantee that * pending signals are serviced. */ set->handles[0] = pgwin32_signal_event; StaticAssertStmt(WSA_INVALID_EVENT == NULL, ""); #endif return set; } /* * Free a previously created WaitEventSet. * * Note: preferably, this shouldn't have to free any resources that could be * inherited across an exec(). If it did, we'd likely leak those resources in * many scenarios. For the epoll case, we ensure that by setting FD_CLOEXEC * when the FD is created. For the Windows case, we assume that the handles * involved are non-inheritable. */ void FreeWaitEventSet(WaitEventSet *set) { #if defined(WAIT_USE_EPOLL) close(set->epoll_fd); #elif defined(WAIT_USE_WIN32) WaitEvent *cur_event; for (cur_event = set->events; cur_event < (set->events + set->nevents); cur_event++) { if (cur_event->events & WL_LATCH_SET) { /* uses the latch's HANDLE */ } else if (cur_event->events & WL_POSTMASTER_DEATH) { /* uses PostmasterHandle */ } else { /* Clean up the event object we created for the socket */ WSAEventSelect(cur_event->fd, NULL, 0); WSACloseEvent(set->handles[cur_event->pos + 1]); } } #endif pfree(set); } /* --- * Add an event to the set. Possible events are: * - WL_LATCH_SET: Wait for the latch to be set * - WL_POSTMASTER_DEATH: Wait for postmaster to die * - WL_SOCKET_READABLE: Wait for socket to become readable, * can be combined in one event with other WL_SOCKET_* events * - WL_SOCKET_WRITEABLE: Wait for socket to become writeable, * can be combined with other WL_SOCKET_* events * - WL_SOCKET_CONNECTED: Wait for socket connection to be established, * can be combined with other WL_SOCKET_* events (on non-Windows * platforms, this is the same as WL_SOCKET_WRITEABLE) * * Returns the offset in WaitEventSet->events (starting from 0), which can be * used to modify previously added wait events using ModifyWaitEvent(). * * In the WL_LATCH_SET case the latch must be owned by the current process, * i.e. it must be a process-local latch initialized with InitLatch, or a * shared latch associated with the current process by calling OwnLatch. * * In the WL_SOCKET_READABLE/WRITEABLE/CONNECTED cases, EOF and error * conditions cause the socket to be reported as readable/writable/connected, * so that the caller can deal with the condition. * * The user_data pointer specified here will be set for the events returned * by WaitEventSetWait(), allowing to easily associate additional data with * events. */ int AddWaitEventToSet(WaitEventSet *set, uint32 events, pgsocket fd, Latch *latch, void *user_data) { WaitEvent *event; /* not enough space */ Assert(set->nevents < set->nevents_space); if (latch) { if (latch->owner_pid != MyProcPid) elog(ERROR, "cannot wait on a latch owned by another process"); if (set->latch) elog(ERROR, "cannot wait on more than one latch"); if ((events & WL_LATCH_SET) != WL_LATCH_SET) elog(ERROR, "latch events only support being set"); } else { if (events & WL_LATCH_SET) elog(ERROR, "cannot wait on latch without a specified latch"); } /* waiting for socket readiness without a socket indicates a bug */ if (fd == PGINVALID_SOCKET && (events & WL_SOCKET_MASK)) elog(ERROR, "cannot wait on socket event without a socket"); event = &set->events[set->nevents]; event->pos = set->nevents++; event->fd = fd; event->events = events; event->user_data = user_data; #ifdef WIN32 event->reset = false; #endif if (events == WL_LATCH_SET) { set->latch = latch; set->latch_pos = event->pos; #ifndef WIN32 event->fd = selfpipe_readfd; #endif } else if (events == WL_POSTMASTER_DEATH) { #ifndef WIN32 event->fd = postmaster_alive_fds[POSTMASTER_FD_WATCH]; #endif } /* perform wait primitive specific initialization, if needed */ #if defined(WAIT_USE_EPOLL) WaitEventAdjustEpoll(set, event, EPOLL_CTL_ADD); #elif defined(WAIT_USE_POLL) WaitEventAdjustPoll(set, event); #elif defined(WAIT_USE_WIN32) WaitEventAdjustWin32(set, event); #endif return event->pos; } /* * Change the event mask and, in the WL_LATCH_SET case, the latch associated * with the WaitEvent. * * 'pos' is the id returned by AddWaitEventToSet. */ void ModifyWaitEvent(WaitEventSet *set, int pos, uint32 events, Latch *latch) { WaitEvent *event; Assert(pos < set->nevents); event = &set->events[pos]; /* * If neither the event mask nor the associated latch changes, return * early. That's an important optimization for some sockets, where * ModifyWaitEvent is frequently used to switch from waiting for reads to * waiting on writes. */ if (events == event->events && (!(event->events & WL_LATCH_SET) || set->latch == latch)) return; if (event->events & WL_LATCH_SET && events != event->events) { /* we could allow to disable latch events for a while */ elog(ERROR, "cannot modify latch event"); } if (event->events & WL_POSTMASTER_DEATH) { elog(ERROR, "cannot modify postmaster death event"); } /* FIXME: validate event mask */ event->events = events; if (events == WL_LATCH_SET) { set->latch = latch; } #if defined(WAIT_USE_EPOLL) WaitEventAdjustEpoll(set, event, EPOLL_CTL_MOD); #elif defined(WAIT_USE_POLL) WaitEventAdjustPoll(set, event); #elif defined(WAIT_USE_WIN32) WaitEventAdjustWin32(set, event); #endif } #if defined(WAIT_USE_EPOLL) /* * action can be one of EPOLL_CTL_ADD | EPOLL_CTL_MOD | EPOLL_CTL_DEL */ static void WaitEventAdjustEpoll(WaitEventSet *set, WaitEvent *event, int action) { struct epoll_event epoll_ev; int rc; /* pointer to our event, returned by epoll_wait */ epoll_ev.data.ptr = event; /* always wait for errors */ epoll_ev.events = EPOLLERR | EPOLLHUP; /* prepare pollfd entry once */ if (event->events == WL_LATCH_SET) { Assert(set->latch != NULL); epoll_ev.events |= EPOLLIN; } else if (event->events == WL_POSTMASTER_DEATH) { epoll_ev.events |= EPOLLIN; } else { Assert(event->fd != PGINVALID_SOCKET); Assert(event->events & (WL_SOCKET_READABLE | WL_SOCKET_WRITEABLE)); if (event->events & WL_SOCKET_READABLE) epoll_ev.events |= EPOLLIN; if (event->events & WL_SOCKET_WRITEABLE) epoll_ev.events |= EPOLLOUT; } /* * Even though unused, we also pass epoll_ev as the data argument if * EPOLL_CTL_DEL is passed as action. There used to be an epoll bug * requiring that, and actually it makes the code simpler... */ rc = epoll_ctl(set->epoll_fd, action, event->fd, &epoll_ev); if (rc < 0) ereport(ERROR, (errcode_for_socket_access(), errmsg("epoll_ctl() failed: %m"))); } #endif #if defined(WAIT_USE_POLL) static void WaitEventAdjustPoll(WaitEventSet *set, WaitEvent *event) { struct pollfd *pollfd = &set->pollfds[event->pos]; pollfd->revents = 0; pollfd->fd = event->fd; /* prepare pollfd entry once */ if (event->events == WL_LATCH_SET) { Assert(set->latch != NULL); pollfd->events = POLLIN; } else if (event->events == WL_POSTMASTER_DEATH) { pollfd->events = POLLIN; } else { Assert(event->events & (WL_SOCKET_READABLE | WL_SOCKET_WRITEABLE)); pollfd->events = 0; if (event->events & WL_SOCKET_READABLE) pollfd->events |= POLLIN; if (event->events & WL_SOCKET_WRITEABLE) pollfd->events |= POLLOUT; } //Assert(event->fd != PGINVALID_SOCKET); } #endif #if defined(WAIT_USE_WIN32) static void WaitEventAdjustWin32(WaitEventSet *set, WaitEvent *event) { HANDLE *handle = &set->handles[event->pos + 1]; if (event->events == WL_LATCH_SET) { Assert(set->latch != NULL); *handle = set->latch->event; } else if (event->events == WL_POSTMASTER_DEATH) { *handle = PostmasterHandle; } else { int flags = FD_CLOSE; /* always check for errors/EOF */ if (event->events & WL_SOCKET_READABLE) flags |= FD_READ; if (event->events & WL_SOCKET_WRITEABLE) flags |= FD_WRITE; if (event->events & WL_SOCKET_CONNECTED) flags |= FD_CONNECT; if (*handle == WSA_INVALID_EVENT) { *handle = WSACreateEvent(); if (*handle == WSA_INVALID_EVENT) elog(ERROR, "failed to create event for socket: error code %u", WSAGetLastError()); } if (WSAEventSelect(event->fd, *handle, flags) != 0) elog(ERROR, "failed to set up event for socket: error code %u", WSAGetLastError()); Assert(event->fd != PGINVALID_SOCKET); } } #endif /* * Wait for events added to the set to happen, or until the timeout is * reached. At most nevents occurred events are returned. * * If timeout = -1, block until an event occurs; if 0, check sockets for * readiness, but don't block; if > 0, block for at most timeout milliseconds. * * Returns the number of events occurred, or 0 if the timeout was reached. * * Returned events will have the fd, pos, user_data fields set to the * values associated with the registered event. */ int WaitEventSetWait(WaitEventSet *set, long timeout, WaitEvent *occurred_events, int nevents) { int returned_events = 0; instr_time start_time; instr_time cur_time; long cur_timeout = -1; Assert(nevents > 0); /* * Initialize timeout if requested. We must record the current time so * that we can determine the remaining timeout if interrupted. */ if (timeout >= 0) { INSTR_TIME_SET_CURRENT(start_time); Assert(timeout >= 0 && timeout <= INT_MAX); cur_timeout = timeout; } #ifndef WIN32 waiting = true; #else /* Ensure that signals are serviced even if latch is already set */ pgwin32_dispatch_queued_signals(); #endif while (returned_events == 0) { int rc; /* * Check if the latch is set already. If so, leave the loop * immediately, avoid blocking again. We don't attempt to report any * other events that might also be satisfied. * * If someone sets the latch between this and the * WaitEventSetWaitBlock() below, the setter will write a byte to the * pipe (or signal us and the signal handler will do that), and the * readiness routine will return immediately. * * On unix, If there's a pending byte in the self pipe, we'll notice * whenever blocking. Only clearing the pipe in that case avoids * having to drain it every time WaitLatchOrSocket() is used. Should * the pipe-buffer fill up we're still ok, because the pipe is in * nonblocking mode. It's unlikely for that to happen, because the * self pipe isn't filled unless we're blocking (waiting = true), or * from inside a signal handler in latch_sigusr1_handler(). * * On windows, we'll also notice if there's a pending event for the * latch when blocking, but there's no danger of anything filling up, * as "Setting an event that is already set has no effect.". * * Note: we assume that the kernel calls involved in latch management * will provide adequate synchronization on machines with weak memory * ordering, so that we cannot miss seeing is_set if a notification * has already been queued. */ if (set->latch && set->latch->is_set) { occurred_events->fd = PGINVALID_SOCKET; occurred_events->pos = set->latch_pos; occurred_events->user_data = set->events[set->latch_pos].user_data; occurred_events->events = WL_LATCH_SET; occurred_events++; returned_events++; break; } /* * Wait for events using the readiness primitive chosen at the top of * this file. If -1 is returned, a timeout has occurred, if 0 we have * to retry, everything >= 1 is the number of returned events. */ rc = WaitEventSetWaitBlock(set, cur_timeout, occurred_events, nevents); if (rc == -1) break; /* timeout occurred */ else returned_events = rc; /* If we're not done, update cur_timeout for next iteration */ if (returned_events == 0 && 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) break; } } #ifndef WIN32 waiting = false; #endif return returned_events; } #if defined(WAIT_USE_EPOLL) /* * 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. * * Be paranoid about a spurious event signalling the postmaster as * being dead. There have been reports about that happening with * older primitives (select(2) to be specific), and a spurious * WL_POSTMASTER_DEATH event would be painful. Re-checking doesn't * cost much. */ 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; } #elif defined(WAIT_USE_POLL) /* * 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. * * Be paranoid about a spurious event signalling the postmaster as * being dead. There have been reports about that happening with * older primitives (select(2) to be specific), and a spurious * WL_POSTMASTER_DEATH event would be painful. Re-checking doesn't * cost much. */ 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; } #elif defined(WAIT_USE_WIN32) /* * Wait using Windows' WaitForMultipleObjects(). * * Unfortunately this will only ever return a single readiness notification at * a time. Note that while the official documentation for * WaitForMultipleObjects is ambiguous about multiple events being "consumed" * with a single bWaitAll = FALSE call, * https://blogs.msdn.microsoft.com/oldnewthing/20150409-00/?p=44273 confirms * that only one event is "consumed". */ static inline int WaitEventSetWaitBlock(WaitEventSet *set, int cur_timeout, WaitEvent *occurred_events, int nevents) { int returned_events = 0; DWORD rc; WaitEvent *cur_event; /* Reset any wait events that need it */ for (cur_event = set->events; cur_event < (set->events + set->nevents); cur_event++) { if (cur_event->reset) { WaitEventAdjustWin32(set, cur_event); cur_event->reset = false; } /* * Windows does not guarantee to log an FD_WRITE network event * indicating that more data can be sent unless the previous send() * failed with WSAEWOULDBLOCK. While our caller might well have made * such a call, we cannot assume that here. Therefore, if waiting for * write-ready, force the issue by doing a dummy send(). If the dummy * send() succeeds, assume that the socket is in fact write-ready, and * return immediately. Also, if it fails with something other than * WSAEWOULDBLOCK, return a write-ready indication to let our caller * deal with the error condition. */ if (cur_event->events & WL_SOCKET_WRITEABLE) { char c; WSABUF buf; DWORD sent; int r; buf.buf = &c; buf.len = 0; r = WSASend(cur_event->fd, &buf, 1, &sent, 0, NULL, NULL); if (r == 0 || WSAGetLastError() != WSAEWOULDBLOCK) { occurred_events->pos = cur_event->pos; occurred_events->user_data = cur_event->user_data; occurred_events->events = WL_SOCKET_WRITEABLE; occurred_events->fd = cur_event->fd; return 1; } } } /* * Sleep. * * Need to wait for ->nevents + 1, because signal handle is in [0]. */ rc = WaitForMultipleObjects(set->nevents + 1, set->handles, FALSE, cur_timeout); /* Check return code */ if (rc == WAIT_FAILED) elog(ERROR, "WaitForMultipleObjects() failed: error code %lu", GetLastError()); else if (rc == WAIT_TIMEOUT) { /* timeout exceeded */ return -1; } if (rc == WAIT_OBJECT_0) { /* Service newly-arrived signals */ pgwin32_dispatch_queued_signals(); return 0; /* retry */ } /* * With an offset of one, due to the always present pgwin32_signal_event, * the handle offset directly corresponds to a wait event. */ cur_event = (WaitEvent *) &set->events[rc - WAIT_OBJECT_0 - 1]; 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) { if (!ResetEvent(set->latch->event)) elog(ERROR, "ResetEvent failed: error code %lu", GetLastError()); 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) { /* * Postmaster apparently died. Since the consequences of falsely * returning WL_POSTMASTER_DEATH could be pretty unpleasant, we take * the trouble to positively verify this with PostmasterIsAlive(), * even though there is no known reason to think that the event could * be falsely set on Windows. */ if (!PostmasterIsAlive()) { occurred_events->fd = PGINVALID_SOCKET; occurred_events->events = WL_POSTMASTER_DEATH; occurred_events++; returned_events++; } } else if (cur_event->events & WL_SOCKET_MASK) { WSANETWORKEVENTS resEvents; HANDLE handle = set->handles[cur_event->pos + 1]; Assert(cur_event->fd); occurred_events->fd = cur_event->fd; ZeroMemory(&resEvents, sizeof(resEvents)); if (WSAEnumNetworkEvents(cur_event->fd, handle, &resEvents) != 0) elog(ERROR, "failed to enumerate network events: error code %u", WSAGetLastError()); if ((cur_event->events & WL_SOCKET_READABLE) && (resEvents.lNetworkEvents & FD_READ)) { /* data available in socket */ occurred_events->events |= WL_SOCKET_READABLE; /*------ * WaitForMultipleObjects doesn't guarantee that a read event will * be returned if the latch is set at the same time. Even if it * did, the caller might drop that event expecting it to reoccur * on next call. So, we must force the event to be reset if this * WaitEventSet is used again in order to avoid an indefinite * hang. Refer https://msdn.microsoft.com/en-us/library/windows/desktop/ms741576(v=vs.85).aspx * for the behavior of socket events. *------ */ cur_event->reset = true; } if ((cur_event->events & WL_SOCKET_WRITEABLE) && (resEvents.lNetworkEvents & FD_WRITE)) { /* writeable */ occurred_events->events |= WL_SOCKET_WRITEABLE; } if ((cur_event->events & WL_SOCKET_CONNECTED) && (resEvents.lNetworkEvents & FD_CONNECT)) { /* connected */ occurred_events->events |= WL_SOCKET_CONNECTED; } if (resEvents.lNetworkEvents & FD_CLOSE) { /* EOF/error, so signal all caller-requested socket flags */ occurred_events->events |= (cur_event->events & WL_SOCKET_MASK); } if (occurred_events->events != 0) { occurred_events++; returned_events++; } } return returned_events; } #endif /* * Read all available data from the self-pipe * * Note: this is only called when waiting = true. If it fails and doesn't * return, it must reset that flag first (though ideally, this will never * happen). */ #ifndef WIN32 static void drainSelfPipe(void) { /* * There shouldn't normally be more than one byte in the pipe, or maybe a * few bytes if multiple processes run SetLatch at the same instant. */ char buf[16]; int rc; for (;;) { rc = read(selfpipe_readfd, buf, sizeof(buf)); if (rc < 0) { if (errno == EAGAIN || errno == EWOULDBLOCK) break; /* the pipe is empty */ else if (errno == EINTR) continue; /* retry */ else { waiting = false; elog(ERROR, "read() on self-pipe failed: %m"); } } else if (rc == 0) { waiting = false; elog(ERROR, "unexpected EOF on self-pipe"); } else if (rc < sizeof(buf)) { /* we successfully drained the pipe; no need to read() again */ break; } /* else buffer wasn't big enough, so read again */ } } #endif /* !WIN32 */ #endif