On Darwin, detect and report a multithreaded postmaster.

Darwin --enable-nls builds use a substitute setlocale() that may start a
thread.  Buildfarm member orangutan experienced BackendList corruption
on account of different postmaster threads executing signal handlers
simultaneously.  Furthermore, a multithreaded postmaster risks undefined
behavior from sigprocmask() and fork().  Emit LOG messages about the
problem and its workaround.  Back-patch to 9.0 (all supported versions).

diff --git a/configure b/configure
index 5136270bb294c43f7b29636cf615a637c7abd021..28526f542fd417fb434991cdcd42c9c4b835e510 100755 (executable)
--- a/configure
+++ b/configure
@@ -19833,7 +19833,8 @@ LIBS=`echo "$LIBS" | sed -e 's/-ledit//g' -e 's/-lreadline//g'`
 
 
 
-for ac_func in cbrt dlopen fdatasync getifaddrs getpeerucred getrlimit mbstowcs_l memmove poll pstat readlink setproctitle setsid sigprocmask symlink sync_file_range towlower utime utimes wcstombs wcstombs_l
+
+for ac_func in cbrt dlopen fdatasync getifaddrs getpeerucred getrlimit mbstowcs_l memmove poll pstat pthread_is_threaded_np readlink setproctitle setsid sigprocmask symlink sync_file_range towlower utime utimes wcstombs wcstombs_l
 do
 as_ac_var=`$as_echo "ac_cv_func_$ac_func" | $as_tr_sh`
 { $as_echo "$as_me:$LINENO: checking for $ac_func" >&5

diff --git a/configure.in b/configure.in
index e946f6503d22ed77c530185393571285e49fedad..51f1807f965468268748511350a01f957b6f5705 100644 (file)
--- a/configure.in
+++ b/configure.in
@@ -1259,7 +1259,7 @@ PGAC_FUNC_GETTIMEOFDAY_1ARG
 LIBS_including_readline="$LIBS"
 LIBS=`echo "$LIBS" | sed -e 's/-ledit//g' -e 's/-lreadline//g'`
 
-AC_CHECK_FUNCS([cbrt dlopen fdatasync getifaddrs getpeerucred getrlimit mbstowcs_l memmove poll pstat readlink setproctitle setsid sigprocmask symlink sync_file_range towlower utime utimes wcstombs wcstombs_l])
+AC_CHECK_FUNCS([cbrt dlopen fdatasync getifaddrs getpeerucred getrlimit mbstowcs_l memmove poll pstat pthread_is_threaded_np readlink setproctitle setsid sigprocmask symlink sync_file_range towlower utime utimes wcstombs wcstombs_l])
 
 AC_REPLACE_FUNCS(fseeko)
 case $host_os in

diff --git a/src/backend/postmaster/postmaster.c b/src/backend/postmaster/postmaster.c
index 3dbf82b339d51d2a5935e91f5b42180532b8425b..d294f9e0af28710d6fa8c904ca20ac1180dc0807 100644 (file)
--- a/src/backend/postmaster/postmaster.c
+++ b/src/backend/postmaster/postmaster.c
@@ -91,6 +91,10 @@
 #include <dns_sd.h>
 #endif
 
+#ifdef HAVE_PTHREAD_IS_THREADED_NP
+#include <pthread.h>
+#endif
+
 #include "access/transam.h"
 #include "access/xlog.h"
 #include "bootstrap/bootstrap.h"
@@ -1233,6 +1237,24 @@ PostmasterMain(int argc, char *argv[])
     */
    RemovePgTempFiles();
 
+#ifdef HAVE_PTHREAD_IS_THREADED_NP
+
+   /*
+    * On Darwin, libintl replaces setlocale() with a version that calls
+    * CFLocaleCopyCurrent() when its second argument is "" and every relevant
+    * environment variable is unset or empty.  CFLocaleCopyCurrent() makes
+    * the process multithreaded.  The postmaster calls sigprocmask() and
+    * calls fork() without an immediate exec(), both of which have undefined
+    * behavior in a multithreaded program.  A multithreaded postmaster is the
+    * normal case on Windows, which offers neither fork() nor sigprocmask().
+    */
+   if (pthread_is_threaded_np() != 0)
+       ereport(LOG,
+               (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+                errmsg("postmaster became multithreaded during startup"),
+        errhint("Set the LC_ALL environment variable to a valid locale.")));
+#endif
+
    /*
     * Remember postmaster startup time
     */
@@ -1675,6 +1697,15 @@ ServerLoop(void)
            TouchSocketLockFiles();
            last_touch_time = now;
        }
+
+#ifdef HAVE_PTHREAD_IS_THREADED_NP
+
+       /*
+        * With assertions enabled, check regularly for appearance of
+        * additional threads.  All builds check at start and exit.
+        */
+       Assert(pthread_is_threaded_np() == 0);
+#endif
    }
 }
 
@@ -4632,6 +4663,18 @@ SubPostmasterMain(int argc, char *argv[])
 static void
 ExitPostmaster(int status)
 {
+#ifdef HAVE_PTHREAD_IS_THREADED_NP
+
+   /*
+    * There is no known cause for a postmaster to become multithreaded after
+    * startup.  Recheck to account for the possibility of unknown causes.
+    */
+   if (pthread_is_threaded_np() != 0)
+       ereport(LOG,
+               (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+                errmsg("postmaster became multithreaded")));
+#endif
+
    /* should cleanup shared memory and kill all backends */
 
    /*

diff --git a/src/include/pg_config.h.in b/src/include/pg_config.h.in
index ce48dfb691cbc3c4cbc587178f8dfc84f404787d..b6a6a48807e47db24941bfca4d928ee122ec0639 100644 (file)
--- a/src/include/pg_config.h.in
+++ b/src/include/pg_config.h.in
@@ -387,6 +387,9 @@
 /* Define if you have POSIX threads libraries and header files. */
 #undef HAVE_PTHREAD
 
+/* Define to 1 if you have the `pthread_is_threaded_np' function. */
+#undef HAVE_PTHREAD_IS_THREADED_NP
+
 /* Define to 1 if you have the <pwd.h> header file. */
 #undef HAVE_PWD_H
 

diff --git a/src/port/exec.c b/src/port/exec.c
index 8ce7c618ffcddca46d023e2caf724e6e07ff6edb..077ac58b2b2aae0341da82905e3a6bf6cd1db559 100644 (file)
--- a/src/port/exec.c
+++ b/src/port/exec.c
@@ -556,8 +556,20 @@ set_pglocale_pgservice(const char *argv0, const char *app)
 
    /* don't set LC_ALL in the backend */
    if (strcmp(app, PG_TEXTDOMAIN("postgres")) != 0)
+   {
        setlocale(LC_ALL, "");
 
+       /*
+        * One could make a case for reproducing here PostmasterMain()'s test
+        * for whether the process is multithreaded.  Unlike the postmaster,
+        * no frontend program calls sigprocmask() or otherwise provides for
+        * mutual exclusion between signal handlers.  While frontends using
+        * fork(), if multithreaded, are formally exposed to undefined
+        * behavior, we have not witnessed a concrete bug.  Therefore,
+        * complaining about multithreading here may be mere pedantry.
+        */
+   }
+
    if (find_my_exec(argv0, my_exec_path) < 0)
        return;