+#if SUPPORTS_WEAK && GTHREAD_USE_WEAK
+
+/* On Solaris 2.6 up to 9, the libc exposes a POSIX threads interface even if
+ -pthreads is not specified. The functions are dummies and most return an
+ error value. However pthread_once returns 0 without invoking the routine
+ it is passed so we cannot pretend that the interface is active if -pthreads
+ is not specified. On Solaris 2.5.1, the interface is not exposed at all so
+ we need to play the usual game with weak symbols. On Solaris 10 and up, a
+ working interface is always exposed. On FreeBSD 6 and later, libc also
+ exposes a dummy POSIX threads interface, similar to what Solaris 2.6 up
+ to 9 does. FreeBSD >= 700014 even provides a pthread_cancel stub in libc,
+ which means the alternate __gthread_active_p below cannot be used there. */
+
+#if defined(__FreeBSD__) || (defined(__sun) && defined(__svr4__))
+
+static volatile int __gthread_active = -1;
+
+static void
+__gthread_trigger (void)
+{
+ __gthread_active = 1;
+}
+
+static inline int
+__gthread_active_p (void)
+{
+ static pthread_mutex_t __gthread_active_mutex = PTHREAD_MUTEX_INITIALIZER;
+ static pthread_once_t __gthread_active_once = PTHREAD_ONCE_INIT;
+
+ /* Avoid reading __gthread_active twice on the main code path. */
+ int __gthread_active_latest_value = __gthread_active;
+
+ /* This test is not protected to avoid taking a lock on the main code
+ path so every update of __gthread_active in a threaded program must
+ be atomic with regard to the result of the test. */
+ if (__builtin_expect (__gthread_active_latest_value < 0, 0))
+ {
+ if (__gthrw_(pthread_once))
+ {
+ /* If this really is a threaded program, then we must ensure that
+ __gthread_active has been set to 1 before exiting this block. */
+ __gthrw_(pthread_mutex_lock) (&__gthread_active_mutex);
+ __gthrw_(pthread_once) (&__gthread_active_once, __gthread_trigger);
+ __gthrw_(pthread_mutex_unlock) (&__gthread_active_mutex);
+ }
+
+ /* Make sure we'll never enter this block again. */
+ if (__gthread_active < 0)
+ __gthread_active = 0;
+
+ __gthread_active_latest_value = __gthread_active;
+ }
+
+ return __gthread_active_latest_value != 0;
+}
+
+#else /* neither FreeBSD nor Solaris */
+