Update.

2001-05-01  Kaz Kylheku  <kaz@ashi.footprints.net>

	Memory barrier overhaul following line by line inspection.
	* mutex.c (pthread_once): Missing memory barriers added.
	* pthread.c (__pthread_wait_for_restart_signal,
	__pthread_timedsuspend_new, __pthread_restart_new): Added
	memory barriers ``just in case'' and for documentary value.
	* spinlock.c (__pthread_release): New inline function for releasing
	spinlock, to complement __pthread_acquire.  Includes memory
	barrier prior to assignment to spinlock, and __asm __volatile
	dance to prevent reordering or optimization of the spinlock access.
	* spinlock.c (__pthread_unlock, __pthread_alt_lock,
	__pthread_alt_timedlock, __pthread_alt_unlock,
	__pthread_compare_and_swap): Updated to use new __pthread_release
	instead of updating spinlock directly.
	* spinlock.c (__pthread_lock, __pthread_unlock, wait_node_alloc,
	wait_node_free, wait_node_dequeue, __pthread_alt_lock,
	__pthread_alt_timedlock, __pthread_alt_unlock, __pthread_acquire):
	Memory barrier overhaul.  Lots of missing memory barriers added,
	a couple needless ones removed.
	* spinlock.c (__pthread_compare_and_swap): testandset optimization
	removed, just calls __pthread_acquire, which has the new read
	barrier in it before its testandset.

1 files changed, 9 insertions, 1 deletions

diff --git a/linuxthreads/pthread.c b/linuxthreads/pthread.c
index 4340a7cc65..e48753b069 100644
--- a/linuxthreads/pthread.c
+++ b/linuxthreads/pthread.c
@@ -941,6 +941,8 @@ void __pthread_wait_for_restart_signal(pthread_descr self)
   do {
     sigsuspend(&mask);                   /* Wait for signal */
   } while (THREAD_GETMEM(self, p_signal) !=__pthread_sig_restart);
+
+  READ_MEMORY_BARRIER(); /* See comment in __pthread_restart_new */
 }
 
 #if !__ASSUME_REALTIME_SIGNALS
@@ -1043,7 +1045,12 @@ __pthread_timedsuspend_old(pthread_descr self, const struct timespec *abstime)
 
 void __pthread_restart_new(pthread_descr th)
 {
-    kill(th->p_pid, __pthread_sig_restart);
+  /* The barrier is proabably not needed, in which case it still documents
+     our assumptions. The intent is to commit previous writes to shared
+     memory so the woken thread will have a consistent view.  Complementary
+     read barriers are present to the suspend functions. */
+  WRITE_MEMORY_BARRIER();
+  kill(th->p_pid, __pthread_sig_restart);
 }
 
 /* There is no __pthread_suspend_new because it would just
@@ -1101,6 +1108,7 @@ __pthread_timedsuspend_new(pthread_descr self, const struct timespec *abstime)
      the caller; the thread is still eligible for a restart wakeup
      so there is a race. */
 
+  READ_MEMORY_BARRIER(); /* See comment in __pthread_restart_new */
   return was_signalled;
 }