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).

1 files changed, 12 insertions, 0 deletions

diff --git a/src/common/exec.c b/src/common/exec.c
index 037bef2210c..cdf20a60af2 100644
--- a/src/common/exec.c
+++ b/src/common/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;