1 files changed, 83 insertions, 0 deletions

diff --git a/gl/m4/pthread-once.m4 b/gl/m4/pthread-once.m4
new file mode 100644
index 00000000..85549254
--- /dev/null
+++ b/gl/m4/pthread-once.m4
@@ -0,0 +1,83 @@
+# pthread-once.m4
+# serial 6
+dnl Copyright (C) 2019-2025 Free Software Foundation, Inc.
+dnl This file is free software; the Free Software Foundation
+dnl gives unlimited permission to copy and/or distribute it,
+dnl with or without modifications, as long as this notice is preserved.
+dnl This file is offered as-is, without any warranty.
+
+AC_DEFUN([gl_PTHREAD_ONCE],
+[
+  AC_REQUIRE([gl_PTHREAD_H])
+  AC_REQUIRE([AC_CANONICAL_HOST])
+  AC_REQUIRE([gl_PTHREADLIB])
+
+  if { case "$host_os" in mingw* | windows*) true;; *) false;; esac; } \
+     && test $gl_threads_api = windows; then
+    dnl Choose function names that don't conflict with the mingw-w64 winpthreads
+    dnl library.
+    REPLACE_PTHREAD_ONCE=1
+    PTHREAD_ONCE_LIB=
+  else
+    if test $HAVE_PTHREAD_H = 0; then
+      HAVE_PTHREAD_ONCE=0
+      PTHREAD_ONCE_LIB=
+    else
+      dnl Work around Cygwin 3.5.3 bug.
+      AC_CACHE_CHECK([whether pthread_once works],
+        [gl_cv_func_pthread_once_works],
+        [case "$host_os" in
+           cygwin*) gl_cv_func_pthread_once_works="guessing no" ;;
+           *)       gl_cv_func_pthread_once_works="yes" ;;
+         esac
+        ])
+      case "$gl_cv_func_pthread_once_works" in
+        *yes) ;;
+        *) REPLACE_PTHREAD_ONCE=1 ;;
+      esac
+      dnl Determine whether linking requires $(LIBPMULTITHREAD) or only
+      dnl $(LIBPTHREAD).
+      if test -z "$LIBPTHREAD" && test -n "$LIBPMULTITHREAD"; then
+        AC_CACHE_CHECK([whether pthread_once can be used without linking with libpthread],
+          [gl_cv_func_pthread_once_no_lib],
+          [AC_RUN_IFELSE(
+             [AC_LANG_PROGRAM(
+                [[#include <pthread.h>
+                  static pthread_once_t a_once = PTHREAD_ONCE_INIT;
+                  static int a;
+                  static void a_init (void) { a = 8647; }
+                ]],
+                [[if (pthread_once (&a_once, a_init)) return 1;
+                  if (a != 8647) return 2;
+                  return 0;
+                ]])],
+             [gl_cv_func_pthread_once_no_lib=yes],
+             [gl_cv_func_pthread_once_no_lib=no],
+             [case "$host_os" in
+                # Guess no on glibc.
+                *-gnu* | gnu*)
+                  gl_cv_func_pthread_once_no_lib="guessing no" ;;
+                # Guess no on FreeBSD.
+                freebsd* | dragonfly* | midnightbsd*)
+                  gl_cv_func_pthread_once_no_lib="guessing no" ;;
+                # Guess yes otherwise.
+                *)
+                  gl_cv_func_pthread_once_no_lib="guessing yes" ;;
+              esac
+             ])
+          ])
+        case "$gl_cv_func_pthread_once_no_lib" in
+          *yes) PTHREAD_ONCE_LIB="$LIBPTHREAD" ;;
+          *)    PTHREAD_ONCE_LIB="$LIBPMULTITHREAD" ;;
+        esac
+        dnl Expected result:
+        dnl PTHREAD_ONCE_LIB is $(LIBPMULTITHREAD) on glibc < 2.34, FreeBSD.
+        dnl PTHREAD_ONCE_LIB is $(LIBPTHREAD) in particular on
+        dnl   musl libc, macOS, NetBSD, Solaris, Cygwin, Haiku, Android.
+      else
+        PTHREAD_ONCE_LIB="$LIBPTHREAD"
+      fi
+    fi
+  fi
+  AC_SUBST([PTHREAD_ONCE_LIB])
+])