From: Bruno Haible <bruno@clisp.org>
Date: Fri, 16 May 2025 13:51:13 +0000 (+0200)
Subject: sigprocmask: Make multithread-safe on native Windows.
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=e9d8c4f480caf32ef072d85d26af68bc9a68d2fb;p=thirdparty%2Fgnulib.git

sigprocmask: Make multithread-safe on native Windows.

* lib/sigprocmask.c: Include glthread/lock.h.
(sig_lock): New variable.
(blocked_set): Remove 'volatile'.
(sigprocmask, _gl_raise_SIGPIPE): Use the sig_lock.
* modules/sigprocmask (Depends-on): Add lock.
* doc/posix-functions/sigprocmask.texi: Mention the async-safety issue.
---

diff --git a/ChangeLog b/ChangeLog
index 95323c3a19..25cced87c6 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,13 @@
+2025-05-16  Bruno Haible  <bruno@clisp.org>
+
+	sigprocmask: Make multithread-safe on native Windows.
+	* lib/sigprocmask.c: Include glthread/lock.h.
+	(sig_lock): New variable.
+	(blocked_set): Remove 'volatile'.
+	(sigprocmask, _gl_raise_SIGPIPE): Use the sig_lock.
+	* modules/sigprocmask (Depends-on): Add lock.
+	* doc/posix-functions/sigprocmask.texi: Mention the async-safety issue.
+
 2025-05-16  Bruno Haible  <bruno@clisp.org>
 
 	pthread-rwlock tests: Add a comment.
diff --git a/doc/posix-functions/sigprocmask.texi b/doc/posix-functions/sigprocmask.texi
index 7683986b3f..02bc537614 100644
--- a/doc/posix-functions/sigprocmask.texi
+++ b/doc/posix-functions/sigprocmask.texi
@@ -28,3 +28,9 @@ multi-threaded programs, in practice it is essentially equivalent to
 return convention.  It's simpler to use @code{sigprocmask}, since it does
 not require linking with @code{-lpthread} on some platforms:
 glibc, NetBSD, OpenBSD, AIX.
+
+Note: While on POSIX platforms, @code{sigprocmask} is multithread-safe
+and async-signal safe (cf. POSIX section ``Signal Actions''
+@url{https://pubs.opengroup.org/onlinepubs/9799919799/functions/V2_chap02.html#tag_16_04_03}),
+the gnulib replacement on native Windows is only multithread-safe,
+not async-signal safe.
diff --git a/lib/sigprocmask.c b/lib/sigprocmask.c
index f79386c8d0..d52e191c44 100644
--- a/lib/sigprocmask.c
+++ b/lib/sigprocmask.c
@@ -24,6 +24,8 @@
 #include <stdint.h>
 #include <stdlib.h>
 
+#include "glthread/lock.h"
+
 #if HAVE_MSVC_INVALID_PARAMETER_HANDLER
 # include "msvc-inval.h"
 #endif
@@ -84,6 +86,10 @@ signal_nothrow (int sig, handler_t handler)
 # define signal signal_nothrow
 #endif
 
+/* This lock protects the variables defined in this file from concurrent
+   modification in multiple threads.  */
+gl_lock_define_initialized(static, sig_lock)
+
 /* Handling of gnulib defined signals.  */
 
 #if GNULIB_defined_SIGPIPE
@@ -182,7 +188,7 @@ sigfillset (sigset_t *set)
 }
 
 /* Set of currently blocked signals.  */
-static volatile sigset_t blocked_set /* = 0 */;
+static sigset_t blocked_set /* = 0 */;
 
 /* Set of currently blocked and pending signals.  */
 static volatile sig_atomic_t pending_array[NSIG] /* = { 0 } */;
@@ -221,6 +227,8 @@ static volatile handler_t old_handlers[NSIG];
 int
 sigprocmask (int operation, const sigset_t *set, sigset_t *old_set)
 {
+  gl_lock_lock (sig_lock);
+
   if (old_set != NULL)
     *old_set = blocked_set;
 
@@ -242,6 +250,7 @@ sigprocmask (int operation, const sigset_t *set, sigset_t *old_set)
           new_blocked_set = blocked_set & ~*set;
           break;
         default:
+          gl_lock_unlock (sig_lock);
           errno = EINVAL;
           return -1;
         }
@@ -286,6 +295,8 @@ sigprocmask (int operation, const sigset_t *set, sigset_t *old_set)
               raise (sig);
         }
     }
+
+  gl_lock_unlock (sig_lock);
   return 0;
 }
 
@@ -334,11 +345,16 @@ rpl_signal (int sig, handler_t handler)
 int
 _gl_raise_SIGPIPE (void)
 {
+  gl_lock_lock (sig_lock);
   if (blocked_set & (1U << SIGPIPE))
-    pending_array[SIGPIPE] = 1;
+    {
+      pending_array[SIGPIPE] = 1;
+      gl_lock_unlock (sig_lock);
+    }
   else
     {
       handler_t handler = SIGPIPE_handler;
+      gl_lock_unlock (sig_lock);
       if (handler == SIG_DFL)
         exit (128 + SIGPIPE);
       else if (handler != SIG_IGN)
diff --git a/modules/sigprocmask b/modules/sigprocmask
index 7f2e083803..79e7c7302f 100644
--- a/modules/sigprocmask
+++ b/modules/sigprocmask
@@ -8,6 +8,7 @@ m4/signalblocking.m4
 Depends-on:
 signal-h
 stdint-h        [test $HAVE_POSIX_SIGNALBLOCKING = 0]
+lock            [test $HAVE_POSIX_SIGNALBLOCKING = 0]
 raise           [test $HAVE_POSIX_SIGNALBLOCKING = 0]
 msvc-inval      [test $HAVE_POSIX_SIGNALBLOCKING = 0]