[Openmp-commits] [openmp] r320150 - Add missing memory barrier for queuing locks

[Jonas Hahnfeld via Openmp-commits]

Author: hahnfeld
Date: Fri Dec  8 07:07:02 2017
New Revision: 320150

URL: http://llvm.org/viewvc/llvm-project?rev=320150&view=rev
Log:
Add missing memory barrier for queuing locks

Otherwise I see hangs in the omp_single_copyprivate test when
compiling in release mode. With the debug assertions, I get a
failure `head > 0 && tail > 0`.

Differential Revision: https://reviews.llvm.org/D40722

Modified:
    openmp/trunk/runtime/src/kmp_lock.cpp
    openmp/trunk/runtime/test/worksharing/single/omp_single_copyprivate.c

Modified: openmp/trunk/runtime/src/kmp_lock.cpp
URL: http://llvm.org/viewvc/llvm-project/openmp/trunk/runtime/src/kmp_lock.cpp?rev=320150&r1=320149&r2=320150&view=diff
==============================================================================
--- openmp/trunk/runtime/src/kmp_lock.cpp (original)
+++ openmp/trunk/runtime/src/kmp_lock.cpp Fri Dec  8 07:07:02 2017
@@ -1456,6 +1456,7 @@ int __kmp_release_queuing_lock(kmp_queui
       }
       dequeued = FALSE;
     } else {
+      KMP_MB();
       tail = *tail_id_p;
       if (head == tail) { /* only one thread on the queue */
 #ifdef DEBUG_QUEUING_LOCKS

Modified: openmp/trunk/runtime/test/worksharing/single/omp_single_copyprivate.c
URL: http://llvm.org/viewvc/llvm-project/openmp/trunk/runtime/test/worksharing/single/omp_single_copyprivate.c?rev=320150&r1=320149&r2=320150&view=diff
==============================================================================
--- openmp/trunk/runtime/test/worksharing/single/omp_single_copyprivate.c (original)
+++ openmp/trunk/runtime/test/worksharing/single/omp_single_copyprivate.c Fri Dec  8 07:07:02 2017
@@ -13,7 +13,7 @@ int test_omp_single_copyprivate()
 
   result = 0;
   nr_iterations = 0;
-  #pragma omp parallel
+  #pragma omp parallel num_threads(4)
   {
     int i;
     for (i = 0; i < LOOPCOUNT; i++)