From 002a689ece50518095b9d0fca71d24128fe9b147 Mon Sep 17 00:00:00 2001 From: Thomas Munro Date: Mon, 6 Feb 2023 13:51:19 +1300 Subject: [PATCH v3 2/3] Use accept4() to accept connections, where available. The postmaster previously accepted connections and then made extra system calls in child processes to make them non-blocking and (as of a recent commit) close-on-exit. On nearly all systems, that can be done atomically with flags to the newer accept4() variant (recently accepted by POSIX for a future revision, but around in the wild for a while now), saving a couple of system calls. The exceptions are Windows, where we didn't have to worry about that problem anyway, EXEC_BACKEND builds on Unix (used by developers only for slightly-more-like-Windows testing), and the straggler Unixes that haven't implemented it yet (at the time of writing: macOS and AIX). Suggested-by: Andres Freund Discussion: https://postgr.es/m/CA%2BhUKGKb6FsAdQWcRL35KJsftv%2B9zXqQbzwkfRf1i0J2e57%2BhQ%40mail.gmail.com --- configure | 12 ++++++++++++ configure.ac | 1 + meson.build | 1 + src/backend/libpq/pqcomm.c | 34 +++++++++++++++++++++++++++------- src/include/pg_config.h.in | 4 ++++ 5 files changed, 45 insertions(+), 7 deletions(-) diff --git a/configure b/configure index e35769ea73..d06f64cdbb 100755 --- a/configure +++ b/configure @@ -16219,6 +16219,18 @@ _ACEOF # We can't use AC_REPLACE_FUNCS to replace these functions, because it # won't handle deployment target restrictions on macOS +ac_fn_c_check_decl "$LINENO" "accept4" "ac_cv_have_decl_accept4" "#include +" +if test "x$ac_cv_have_decl_accept4" = xyes; then : + ac_have_decl=1 +else + ac_have_decl=0 +fi + +cat >>confdefs.h <<_ACEOF +#define HAVE_DECL_ACCEPT4 $ac_have_decl +_ACEOF + ac_fn_c_check_decl "$LINENO" "preadv" "ac_cv_have_decl_preadv" "#include " if test "x$ac_cv_have_decl_preadv" = xyes; then : diff --git a/configure.ac b/configure.ac index af23c15cb2..070a0b33db 100644 --- a/configure.ac +++ b/configure.ac @@ -1843,6 +1843,7 @@ AC_CHECK_DECLS([strlcat, strlcpy, strnlen]) # We can't use AC_REPLACE_FUNCS to replace these functions, because it # won't handle deployment target restrictions on macOS +AC_CHECK_DECLS([accept4], [], [], [#include ]) AC_CHECK_DECLS([preadv], [], [AC_LIBOBJ(preadv)], [#include ]) AC_CHECK_DECLS([pwritev], [], [AC_LIBOBJ(pwritev)], [#include ]) diff --git a/meson.build b/meson.build index f534704452..3e15d6c825 100644 --- a/meson.build +++ b/meson.build @@ -2097,6 +2097,7 @@ decl_checks = [ # checking for library symbols wouldn't handle deployment target # restrictions on macOS decl_checks += [ + ['accept4', 'sys/socket.h'], ['preadv', 'sys/uio.h'], ['pwritev', 'sys/uio.h'], ] diff --git a/src/backend/libpq/pqcomm.c b/src/backend/libpq/pqcomm.c index 0ccec33af4..70734f1a4b 100644 --- a/src/backend/libpq/pqcomm.c +++ b/src/backend/libpq/pqcomm.c @@ -184,6 +184,14 @@ pq_init(void) /* set up process-exit hook to close the socket */ on_proc_exit(socket_close, 0); +#ifndef WIN32 + /* + * On most systems, the socket has already been made non-blocking and + * close-on-exec by StreamConnection(). On systems that don't have + * accept4() yet, and EXEC_BACKEND builds that need the socket to survive + * exec*(), we do that separately here in the child process. + */ +#if !HAVE_DECL_ACCEPT4 || defined(EXEC_BACKEND) /* * In backends (as soon as forked) we operate the underlying socket in * nonblocking mode and use latches to implement blocking semantics if @@ -194,13 +202,9 @@ pq_init(void) * the client, which might require changing the mode again, leading to * infinite recursion. */ -#ifndef WIN32 if (!pg_set_noblock(MyProcPort->sock)) ereport(COMMERROR, (errmsg("could not set socket to nonblocking mode: %m"))); -#endif - -#ifndef WIN32 /* * Also make sure that any subprocesses that execute a new program don't @@ -208,6 +212,7 @@ pq_init(void) */ if (fcntl(MyProcPort->sock, F_SETFD, FD_CLOEXEC) < 0) elog(FATAL, "fcntl(F_SETFD) failed on socket: %m"); +#endif #endif FeBeWaitSet = CreateWaitEventSet(TopMemoryContext, FeBeWaitSetNEvents); @@ -702,9 +707,24 @@ StreamConnection(pgsocket server_fd, Port *port) { /* accept connection and fill in the client (remote) address */ port->raddr.salen = sizeof(port->raddr.addr); - if ((port->sock = accept(server_fd, - (struct sockaddr *) &port->raddr.addr, - &port->raddr.salen)) == PGINVALID_SOCKET) + +#if HAVE_DECL_ACCEPT4 && !defined(EXEC_BACKEND) + /* + * If we have accept4(), we can avoid a couple of fcntl() calls in + * pq_init(). We can't use this optimization in EXEC_BACKEND builds, + * though, because they need the socket to survive exec(). + */ + port->sock = accept4(server_fd, + (struct sockaddr *) &port->raddr.addr, + &port->raddr.salen, + SOCK_CLOEXEC | SOCK_NONBLOCK); +#else + port->sock = accept(server_fd, + (struct sockaddr *) &port->raddr.addr, + &port->raddr.salen); +#endif + + if (port->sock == PGINVALID_SOCKET) { ereport(LOG, (errcode_for_socket_access(), diff --git a/src/include/pg_config.h.in b/src/include/pg_config.h.in index 20c82f5979..e21d0f05f5 100644 --- a/src/include/pg_config.h.in +++ b/src/include/pg_config.h.in @@ -91,6 +91,10 @@ /* Define to 1 if you have the `CRYPTO_lock' function. */ #undef HAVE_CRYPTO_LOCK +/* Define to 1 if you have the declaration of `accept4', and to 0 if you + don't. */ +#undef HAVE_DECL_ACCEPT4 + /* Define to 1 if you have the declaration of `fdatasync', and to 0 if you don't. */ #undef HAVE_DECL_FDATASYNC -- 2.39.1