I pushed the small preliminary patches. Here's a rebase of the main patch.
From d23fba75cf693ffabc068a36424b7be22342c1b2 Mon Sep 17 00:00:00 2001 From: Thomas Munro <thomas.mu...@gmail.com> Date: Wed, 9 Nov 2022 22:59:58 +1300 Subject: [PATCH v7] Give the postmaster a WaitEventSet and a latch.
Traditionally, the postmaster's architecture was quite unusual. It did a lot of work inside signal handlers, which were only unblocked while waiting in select() to make that safe. Switch to a more typical architecture, where signal handlers just set flags and use a latch to close races. Now the postmaster looks like all other PostgreSQL processes, multiplexing its event processing in epoll_wait()/kevent()/poll()/WaitForMultipleObjects() depending on the OS. Changes: * Allow the postmaster to set up its own local latch. For now we don't want other backends setting the postmaster's latch directly (that would require latches robust against arbitrary corruption of shared memory). * The existing signal handlers are cut in two: a handle_XXX part that sets a pending_XXX variable and sets the local latch, and a process_XXX part. * Signal handlers are now installed with the regular pqsignal() function rather then the special pqsignal_pm() function; the concerns about the portability of SA_RESTART vs select() are no longer relevant: SUSv2 left it implementation-defined whether select() restarts, but didn't add that qualification for poll(), and it doesn't matter anyway because we call SetLatch() creating a new reason to wake up. Reviewed-by: Andres Freund <and...@anarazel.de> Discussion: https://postgr.es/m/CA%2BhUKG%2BZ-HpOj1JsO9eWUP%2Bar7npSVinsC_npxSy%2BjdOMsx%3DGg%40mail.gmail.com --- src/backend/libpq/pqsignal.c | 40 --- src/backend/postmaster/fork_process.c | 12 +- src/backend/postmaster/postmaster.c | 379 ++++++++++++++------------ src/backend/tcop/postgres.c | 1 - src/backend/utils/init/miscinit.c | 13 +- src/include/libpq/pqsignal.h | 3 - src/include/miscadmin.h | 1 + 7 files changed, 225 insertions(+), 224 deletions(-) diff --git a/src/backend/libpq/pqsignal.c b/src/backend/libpq/pqsignal.c index 1ab34c5214..718043a39d 100644 --- a/src/backend/libpq/pqsignal.c +++ b/src/backend/libpq/pqsignal.c @@ -97,43 +97,3 @@ pqinitmask(void) sigdelset(&StartupBlockSig, SIGALRM); #endif } - -/* - * Set up a postmaster signal handler for signal "signo" - * - * Returns the previous handler. - * - * This is used only in the postmaster, which has its own odd approach to - * signal handling. For signals with handlers, we block all signals for the - * duration of signal handler execution. We also do not set the SA_RESTART - * flag; this should be safe given the tiny range of code in which the - * postmaster ever unblocks signals. - * - * pqinitmask() must have been invoked previously. - */ -pqsigfunc -pqsignal_pm(int signo, pqsigfunc func) -{ - struct sigaction act, - oact; - - act.sa_handler = func; - if (func == SIG_IGN || func == SIG_DFL) - { - /* in these cases, act the same as pqsignal() */ - sigemptyset(&act.sa_mask); - act.sa_flags = SA_RESTART; - } - else - { - act.sa_mask = BlockSig; - act.sa_flags = 0; - } -#ifdef SA_NOCLDSTOP - if (signo == SIGCHLD) - act.sa_flags |= SA_NOCLDSTOP; -#endif - if (sigaction(signo, &act, &oact) < 0) - return SIG_ERR; - return oact.sa_handler; -} diff --git a/src/backend/postmaster/fork_process.c b/src/backend/postmaster/fork_process.c index ec67761487..e1e7d91c52 100644 --- a/src/backend/postmaster/fork_process.c +++ b/src/backend/postmaster/fork_process.c @@ -12,24 +12,28 @@ #include "postgres.h" #include <fcntl.h> +#include <signal.h> #include <time.h> #include <sys/stat.h> #include <sys/time.h> #include <unistd.h> +#include "libpq/pqsignal.h" #include "postmaster/fork_process.h" #ifndef WIN32 /* * Wrapper for fork(). Return values are the same as those for fork(): * -1 if the fork failed, 0 in the child process, and the PID of the - * child in the parent process. + * child in the parent process. Signals are blocked while forking, so + * the child must unblock. */ pid_t fork_process(void) { pid_t result; const char *oomfilename; + sigset_t save_mask; #ifdef LINUX_PROFILE struct itimerval prof_itimer; @@ -51,6 +55,7 @@ fork_process(void) getitimer(ITIMER_PROF, &prof_itimer); #endif + sigprocmask(SIG_SETMASK, &BlockSig, &save_mask); result = fork(); if (result == 0) { @@ -103,6 +108,11 @@ fork_process(void) /* do post-fork initialization for random number generation */ pg_strong_random_init(); } + else + { + /* in parent, restore signal mask */ + sigprocmask(SIG_SETMASK, &save_mask, NULL); + } return result; } diff --git a/src/backend/postmaster/postmaster.c b/src/backend/postmaster/postmaster.c index f459dab360..e107c18ff7 100644 --- a/src/backend/postmaster/postmaster.c +++ b/src/backend/postmaster/postmaster.c @@ -70,7 +70,6 @@ #include <time.h> #include <sys/wait.h> #include <ctype.h> -#include <sys/select.h> #include <sys/stat.h> #include <sys/socket.h> #include <fcntl.h> @@ -362,6 +361,15 @@ static volatile sig_atomic_t WalReceiverRequested = false; static volatile bool StartWorkerNeeded = true; static volatile bool HaveCrashedWorker = false; +/* set when signals arrive */ +static volatile sig_atomic_t pending_action_request; +static volatile sig_atomic_t pending_child_exit; +static volatile sig_atomic_t pending_reload_request; +static volatile sig_atomic_t pending_shutdown_request; + +/* I/O multiplexing object */ +static WaitEventSet *wait_set; + #ifdef USE_SSL /* Set when and if SSL has been initialized properly */ static bool LoadedSSL = false; @@ -380,10 +388,14 @@ static void getInstallationPaths(const char *argv0); static void checkControlFile(void); static Port *ConnCreate(int serverFd); static void ConnFree(Port *port); -static void SIGHUP_handler(SIGNAL_ARGS); -static void pmdie(SIGNAL_ARGS); -static void reaper(SIGNAL_ARGS); -static void sigusr1_handler(SIGNAL_ARGS); +static void handle_action_request_signal(SIGNAL_ARGS); +static void handle_child_exit_signal(SIGNAL_ARGS); +static void handle_reload_request_signal(SIGNAL_ARGS); +static void handle_shutdown_request_signal(SIGNAL_ARGS); +static void process_action_request(void); +static void process_child_exit(void); +static void process_reload_request(void); +static void process_shutdown_request(void); static void process_startup_packet_die(SIGNAL_ARGS); static void dummy_handler(SIGNAL_ARGS); static void StartupPacketTimeoutHandler(void); @@ -401,7 +413,6 @@ static int BackendStartup(Port *port); static int ProcessStartupPacket(Port *port, bool ssl_done, bool gss_done); static void SendNegotiateProtocolVersion(List *unrecognized_protocol_options); static void processCancelRequest(Port *port, void *pkt); -static int initMasks(fd_set *rmask); static void report_fork_failure_to_client(Port *port, int errnum); static CAC_state canAcceptConnections(int backend_type); static bool RandomCancelKey(int32 *cancel_key); @@ -609,26 +620,6 @@ PostmasterMain(int argc, char *argv[]) /* * Set up signal handlers for the postmaster process. * - * In the postmaster, we use pqsignal_pm() rather than pqsignal() (which - * is used by all child processes and client processes). That has a - * couple of special behaviors: - * - * 1. We tell sigaction() to block all signals for the duration of the - * signal handler. This is faster than our old approach of - * blocking/unblocking explicitly in the signal handler, and it should also - * prevent excessive stack consumption if signals arrive quickly. - * - * 2. We do not set the SA_RESTART flag. This is because signals will 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 can respond if anything interesting happened. - * On some platforms, signals marked SA_RESTART would not cause the - * select() wait to end. - * - * Child processes will generally want SA_RESTART, so pqsignal() sets that - * flag. We expect children to set up their own handlers before - * unblocking signals. - * * CAUTION: when changing this list, check for side-effects on the signal * handling setup of child processes. See tcop/postgres.c, * bootstrap/bootstrap.c, postmaster/bgwriter.c, postmaster/walwriter.c, @@ -638,26 +629,21 @@ PostmasterMain(int argc, char *argv[]) pqinitmask(); PG_SETMASK(&BlockSig); - pqsignal_pm(SIGHUP, SIGHUP_handler); /* reread config file and have - * children do same */ - pqsignal_pm(SIGINT, pmdie); /* send SIGTERM and shut down */ - pqsignal_pm(SIGQUIT, pmdie); /* send SIGQUIT and die */ - pqsignal_pm(SIGTERM, pmdie); /* wait for children and shut down */ - pqsignal_pm(SIGALRM, SIG_IGN); /* ignored */ - pqsignal_pm(SIGPIPE, SIG_IGN); /* ignored */ - pqsignal_pm(SIGUSR1, sigusr1_handler); /* message from child process */ - pqsignal_pm(SIGUSR2, dummy_handler); /* unused, reserve for children */ - pqsignal_pm(SIGCHLD, reaper); /* handle child termination */ + pqsignal(SIGHUP, handle_reload_request_signal); + pqsignal(SIGINT, handle_shutdown_request_signal); + pqsignal(SIGQUIT, handle_shutdown_request_signal); + pqsignal(SIGTERM, handle_shutdown_request_signal); + pqsignal(SIGALRM, SIG_IGN); /* ignored */ + pqsignal(SIGPIPE, SIG_IGN); /* ignored */ + pqsignal(SIGUSR1, handle_action_request_signal); + pqsignal(SIGUSR2, dummy_handler); /* unused, reserve for children */ + pqsignal(SIGCHLD, handle_child_exit_signal); -#ifdef SIGURG + /* This may configure SIGURG, depending on platform. */ + InitializeLatchSupport(); + InitProcessLocalLatch(); - /* - * Ignore SIGURG for now. Child processes may change this (see - * InitializeLatchSupport), but they will not receive any such signals - * until they wait on a latch. - */ - pqsignal_pm(SIGURG, SIG_IGN); /* ignored */ -#endif + PG_SETMASK(&UnBlockSig); /* * No other place in Postgres should touch SIGTTIN/SIGTTOU handling. We @@ -667,15 +653,15 @@ PostmasterMain(int argc, char *argv[]) * child processes should just allow the inherited settings to stand. */ #ifdef SIGTTIN - pqsignal_pm(SIGTTIN, SIG_IGN); /* ignored */ + pqsignal(SIGTTIN, SIG_IGN); /* ignored */ #endif #ifdef SIGTTOU - pqsignal_pm(SIGTTOU, SIG_IGN); /* ignored */ + pqsignal(SIGTTOU, SIG_IGN); /* ignored */ #endif /* ignore SIGXFSZ, so that ulimit violations work like disk full */ #ifdef SIGXFSZ - pqsignal_pm(SIGXFSZ, SIG_IGN); /* ignored */ + pqsignal(SIGXFSZ, SIG_IGN); /* ignored */ #endif /* @@ -1698,6 +1684,37 @@ DetermineSleepTime(struct timeval *timeout) } } +/* + * Activate or deactivate notifications of server socket events. Since we + * don't currently have a way to remove events from an existing WaitEventSet, + * we'll just destroy and recreate the whole thing. This is called during + * shutdown so we can wait for backends to exit without accepting new + * connections, and during crash reinitialization when we need to start + * listening for new connections again. + */ +static void +ConfigurePostmasterWaitSet(bool accept_connections) +{ + if (wait_set) + FreeWaitEventSet(wait_set); + wait_set = NULL; + + wait_set = CreateWaitEventSet(CurrentMemoryContext, 1 + MAXLISTEN); + AddWaitEventToSet(wait_set, WL_LATCH_SET, PGINVALID_SOCKET, MyLatch, NULL); + + if (accept_connections) + { + for (int i = 0; i < MAXLISTEN; i++) + { + int fd = ListenSocket[i]; + + if (fd == PGINVALID_SOCKET) + break; + AddWaitEventToSet(wait_set, WL_SOCKET_ACCEPT, fd, NULL, NULL); + } + } +} + /* * Main idle loop of postmaster * @@ -1706,97 +1723,62 @@ DetermineSleepTime(struct timeval *timeout) static int ServerLoop(void) { - fd_set readmask; - int nSockets; time_t last_lockfile_recheck_time, last_touch_time; + WaitEvent events[MAXLISTEN]; + int nevents; + ConfigurePostmasterWaitSet(true); last_lockfile_recheck_time = last_touch_time = time(NULL); - nSockets = initMasks(&readmask); - for (;;) { - fd_set rmask; - int selres; time_t now; + struct timeval timeout; - /* - * Wait for a connection request to arrive. - * - * 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); + DetermineSleepTime(&timeout); - pg_usleep(100000L); /* 100 msec seems reasonable */ - selres = 0; - - PG_SETMASK(&BlockSig); - } - else - { - /* must set timeout each time; some OSes change it! */ - struct timeval timeout; - - /* Needs to run with blocked signals! */ - DetermineSleepTime(&timeout); - - PG_SETMASK(&UnBlockSig); - - selres = select(nSockets, &rmask, NULL, NULL, &timeout); - - PG_SETMASK(&BlockSig); - } - - /* Now check the select() result */ - if (selres < 0) - { - if (errno != EINTR && errno != EWOULDBLOCK) - { - ereport(LOG, - (errcode_for_socket_access(), - errmsg("select() failed in postmaster: %m"))); - return STATUS_ERROR; - } - } + nevents = WaitEventSetWait(wait_set, + timeout.tv_sec * 1000 + timeout.tv_usec / 1000, + events, + lengthof(events), + 0 /* postmaster posts no wait_events */); /* - * New connection pending on any of our sockets? If so, fork a child - * process to deal with it. + * Latch set by signal handler, or new connection pending on any of our + * sockets? If the latter, fork a child process to deal with it. */ - if (selres > 0) + for (int i = 0; i < nevents; i++) { - int i; - - for (i = 0; i < MAXLISTEN; i++) + if (events[i].events & WL_LATCH_SET) { - if (ListenSocket[i] == PGINVALID_SOCKET) - break; - if (FD_ISSET(ListenSocket[i], &rmask)) + ResetLatch(MyLatch); + + /* Process work scheduled by signal handlers. */ + if (pending_shutdown_request) + process_shutdown_request(); + if (pending_child_exit) + process_child_exit(); + if (pending_reload_request) + process_reload_request(); + if (pending_action_request) + process_action_request(); + } + else if (events[i].events & WL_SOCKET_ACCEPT) + { + Port *port; + + port = ConnCreate(events[i].fd); + if (port) { - Port *port; + BackendStartup(port); - port = ConnCreate(ListenSocket[i]); - if (port) - { - BackendStartup(port); - - /* - * We no longer need the open socket or port structure - * in this process - */ - StreamClose(port->sock); - ConnFree(port); - } + /* + * We no longer need the open socket or port structure + * in this process + */ + StreamClose(port->sock); + ConnFree(port); } } } @@ -1939,34 +1921,6 @@ ServerLoop(void) } } -/* - * Initialise the masks for select() for the ports we are listening on. - * Return the number of sockets to listen on. - */ -static int -initMasks(fd_set *rmask) -{ - int maxsock = -1; - int i; - - FD_ZERO(rmask); - - for (i = 0; i < MAXLISTEN; i++) - { - int fd = ListenSocket[i]; - - if (fd == PGINVALID_SOCKET) - break; - FD_SET(fd, rmask); - - if (fd > maxsock) - maxsock = fd; - } - - return maxsock + 1; -} - - /* * Read a client's startup packet and do something according to it. * @@ -2609,6 +2563,10 @@ ClosePostmasterPorts(bool am_syslogger) { int i; + /* Release resources held by the postmaster's WaitEventSet. */ + if (wait_set) + FreeWaitEventSetAfterFork(wait_set); + #ifndef WIN32 /* @@ -2707,14 +2665,45 @@ InitProcessGlobals(void) #endif } +/* + * Child processes use SIGUSR1 to send 'pmsignals'. pg_ctl uses SIGUSR1 to ask + * postmaster to check for logrotate and promote files. + */ +static void +handle_action_request_signal(SIGNAL_ARGS) +{ + int save_errno = errno; + + pending_action_request = true; + SetLatch(MyLatch); + + errno = save_errno; +} /* - * SIGHUP -- reread config files, and tell children to do same + * pg_ctl uses SIGHUP to request a reload of the configuration files. */ static void -SIGHUP_handler(SIGNAL_ARGS) +handle_reload_request_signal(SIGNAL_ARGS) { - int save_errno = errno; + int save_errno = errno; + + pending_reload_request = true; + SetLatch(MyLatch); + + errno = save_errno; +} + +/* + * Re-read config files, and tell children to do same. + */ +static void +process_reload_request(void) +{ + pending_reload_request = false; + + ereport(DEBUG2, + (errmsg_internal("postmaster received reload request signal"))); if (Shutdown <= SmartShutdown) { @@ -2771,27 +2760,50 @@ SIGHUP_handler(SIGNAL_ARGS) write_nondefault_variables(PGC_SIGHUP); #endif } +} + +/* + * pg_ctl uses SIGTERM, SIGINT and SIGQUIT to request different types of + * shutdown. + */ +static void +handle_shutdown_request_signal(SIGNAL_ARGS) +{ + int save_errno = errno; + + switch (postgres_signal_arg) + { + case SIGTERM: + pending_shutdown_request = SmartShutdown; + break; + case SIGINT: + pending_shutdown_request = FastShutdown; + break; + case SIGQUIT: + pending_shutdown_request = ImmediateShutdown; + break; + } + SetLatch(MyLatch); errno = save_errno; } - /* - * pmdie -- signal handler for processing various postmaster signals. + * Process shutdown request. */ static void -pmdie(SIGNAL_ARGS) +process_shutdown_request(void) { - int save_errno = errno; + int mode = pending_shutdown_request; ereport(DEBUG2, - (errmsg_internal("postmaster received signal %d", - postgres_signal_arg))); + (errmsg_internal("postmaster received shutdown request signal"))); - switch (postgres_signal_arg) - { - case SIGTERM: + pending_shutdown_request = NoShutdown; + switch (mode) + { + case SmartShutdown: /* * Smart Shutdown: * @@ -2830,7 +2842,7 @@ pmdie(SIGNAL_ARGS) PostmasterStateMachine(); break; - case SIGINT: + case FastShutdown: /* * Fast Shutdown: @@ -2871,7 +2883,7 @@ pmdie(SIGNAL_ARGS) PostmasterStateMachine(); break; - case SIGQUIT: + case ImmediateShutdown: /* * Immediate Shutdown: @@ -2908,20 +2920,30 @@ pmdie(SIGNAL_ARGS) PostmasterStateMachine(); break; } +} + +static void +handle_child_exit_signal(SIGNAL_ARGS) +{ + int save_errno = errno; + + pending_child_exit = true; + SetLatch(MyLatch); errno = save_errno; } /* - * Reaper -- signal handler to cleanup after a child process dies. + * Cleanup after a child process dies. */ static void -reaper(SIGNAL_ARGS) +process_child_exit(void) { - int save_errno = errno; int pid; /* process id of dead child process */ int exitstatus; /* its exit status */ + pending_child_exit = false; + ereport(DEBUG4, (errmsg_internal("reaping dead processes"))); @@ -3213,8 +3235,6 @@ reaper(SIGNAL_ARGS) * or actions to make. */ PostmasterStateMachine(); - - errno = save_errno; } /* @@ -3642,8 +3662,9 @@ LogChildExit(int lev, const char *procname, int pid, int exitstatus) /* * Advance the postmaster's state machine and take actions as appropriate * - * This is common code for pmdie(), reaper() and sigusr1_handler(), which - * receive the signals that might mean we need to change state. + * This is common code for process_shutdown_request(), process_child_exit() and + * process_action_request(), which process the signals that might mean we need + * to change state. */ static void PostmasterStateMachine(void) @@ -3796,6 +3817,9 @@ PostmasterStateMachine(void) if (pmState == PM_WAIT_DEAD_END) { + /* Don't allow any new socket connection events. */ + ConfigurePostmasterWaitSet(false); + /* * PM_WAIT_DEAD_END state ends when the BackendList is entirely empty * (ie, no dead_end children remain), and the archiver is gone too. @@ -3905,6 +3929,9 @@ PostmasterStateMachine(void) pmState = PM_STARTUP; /* crash recovery started, reset SIGKILL flag */ AbortStartTime = 0; + + /* start accepting server socket connection events again */ + ConfigurePostmasterWaitSet(true); } } @@ -5013,12 +5040,16 @@ ExitPostmaster(int status) } /* - * sigusr1_handler - handle signal conditions from child processes + * Handle pmsignal conditions representing requests from backends, + * and check for promote and logrotate requests from pg_ctl. */ static void -sigusr1_handler(SIGNAL_ARGS) +process_action_request(void) { - int save_errno = errno; + pending_action_request = false; + + ereport(DEBUG2, + (errmsg_internal("postmaster received action request signal"))); /* * RECOVERY_STARTED and BEGIN_HOT_STANDBY signals are ignored in @@ -5159,8 +5190,6 @@ sigusr1_handler(SIGNAL_ARGS) */ signal_child(StartupPID, SIGUSR2); } - - errno = save_errno; } /* diff --git a/src/backend/tcop/postgres.c b/src/backend/tcop/postgres.c index 01d264b5ab..9b320889b0 100644 --- a/src/backend/tcop/postgres.c +++ b/src/backend/tcop/postgres.c @@ -24,7 +24,6 @@ #include <signal.h> #include <unistd.h> #include <sys/resource.h> -#include <sys/select.h> #include <sys/socket.h> #include <sys/time.h> diff --git a/src/backend/utils/init/miscinit.c b/src/backend/utils/init/miscinit.c index eb1046450b..1a8885b73e 100644 --- a/src/backend/utils/init/miscinit.c +++ b/src/backend/utils/init/miscinit.c @@ -135,8 +135,7 @@ InitPostmasterChild(void) /* Initialize process-local latch support */ InitializeLatchSupport(); - MyLatch = &LocalLatchData; - InitLatch(MyLatch); + InitProcessLocalLatch(); InitializeLatchWaitSet(); /* @@ -189,8 +188,7 @@ InitStandaloneProcess(const char *argv0) /* Initialize process-local latch support */ InitializeLatchSupport(); - MyLatch = &LocalLatchData; - InitLatch(MyLatch); + InitProcessLocalLatch(); InitializeLatchWaitSet(); /* @@ -232,6 +230,13 @@ SwitchToSharedLatch(void) SetLatch(MyLatch); } +void +InitProcessLocalLatch(void) +{ + MyLatch = &LocalLatchData; + InitLatch(MyLatch); +} + void SwitchBackToLocalLatch(void) { diff --git a/src/include/libpq/pqsignal.h b/src/include/libpq/pqsignal.h index 7890b426a8..76eb380a4f 100644 --- a/src/include/libpq/pqsignal.h +++ b/src/include/libpq/pqsignal.h @@ -53,7 +53,4 @@ extern PGDLLIMPORT sigset_t StartupBlockSig; extern void pqinitmask(void); -/* pqsigfunc is declared in src/include/port.h */ -extern pqsigfunc pqsignal_pm(int signo, pqsigfunc func); - #endif /* PQSIGNAL_H */ diff --git a/src/include/miscadmin.h b/src/include/miscadmin.h index 795182fa51..f64f81cf00 100644 --- a/src/include/miscadmin.h +++ b/src/include/miscadmin.h @@ -310,6 +310,7 @@ extern PGDLLIMPORT char *DatabasePath; /* now in utils/init/miscinit.c */ extern void InitPostmasterChild(void); extern void InitStandaloneProcess(const char *argv0); +extern void InitProcessLocalLatch(void); extern void SwitchToSharedLatch(void); extern void SwitchBackToLocalLatch(void); -- 2.38.1
