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Re: [PATCH] Fix PR target/24071
> The alternative would be, inside the mutex:
>
> if (__gthread_active < 0) {
> __gthread_active = 0;
> __gthrw_(pthread_once) (...);
> }
>
> and then, instead of "__gthread_active++":
>
> else
> __gthread_active = 0;
On second thoughts, I don't think this is safe. The first test in my patch
if (__gthread_active < 0)
is not protected to avoid taking a lock on the main code path so
__gthread_active must never be 0 when the program is threaded.
However I agree that the increment is potentially confusing so we'd probably
better eliminate it. I've also decided to make __gthread_active volatile
for the sake of extra-safety (I think your modification would also have been
problematic wrt that aspect). Revised version attached, same testing.
--
Eric Botcazou
Index: gthr-posix95.h
===================================================================
--- gthr-posix95.h (revision 118142)
+++ gthr-posix95.h (working copy)
@@ -109,6 +109,59 @@ __gthrw(pthread_setschedparam)
#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. */
+
+#if 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 /* not Solaris */
+
static inline int
__gthread_active_p (void)
{
@@ -117,6 +170,8 @@ __gthread_active_p (void)
return __gthread_active_ptr != 0;
}
+#endif /* Solaris */
+
#else /* not SUPPORTS_WEAK */
static inline int
Index: gthr-posix.h
===================================================================
--- gthr-posix.h (revision 118142)
+++ gthr-posix.h (working copy)
@@ -142,6 +142,59 @@ __gthrw(pthread_setschedparam)
#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. */
+
+#if 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 /* not Solaris */
+
static inline int
__gthread_active_p (void)
{
@@ -150,6 +203,8 @@ __gthread_active_p (void)
return __gthread_active_ptr != 0;
}
+#endif /* Solaris */
+
#else /* not SUPPORTS_WEAK */
static inline int