[Openmp-commits] [PATCH] D29597: Fixed intermittent hang on tests with "target teams if(0)" construct with no parallel inside

Andrey Churbanov via Phabricator via Openmp-commits openmp-commits at lists.llvm.org
Mon Feb 6 11:28:35 PST 2017

AndreyChurbanov created this revision.

Our testing found that the change r294214 has one issue with offload corner-case tests those have the code fragment:

#pragma omp target teams if(target:0)

where intermittent hang observed. Investigation showed that when master thread executes spin loop waiting for SAFE reap state of the worker thread this worker may be sleeping on a fork barrier.  The solution for the problem is to check the flag the worker thread sleeps on, and resume the worker if needed so that it can mark itself as SAFE to reap.




Index: runtime/src/kmp_runtime.cpp
--- runtime/src/kmp_runtime.cpp
+++ runtime/src/kmp_runtime.cpp
@@ -5265,18 +5265,22 @@
             // Wait for threads to reach reapable state
             for (f = 1; f < team->t.t_nproc; ++f) {
-                volatile kmp_uint32 *state = &team->t.t_threads[f]->th.th_reap_state;
+                kmp_info_t *th = team->t.t_threads[f];
+                volatile kmp_uint32 *state = &th->th.th_reap_state;
                 while (*state != KMP_SAFE_TO_REAP) {
                     // On Windows a thread can be killed at any time, check this
                     DWORD ecode;
-                    if (__kmp_is_thread_alive(team->t.t_threads[f], &ecode))
-                        KMP_CPU_PAUSE();
-                    else
+                    if (!__kmp_is_thread_alive(th, &ecode)) {
                         *state = KMP_SAFE_TO_REAP; // reset the flag for dead thread
-                    KMP_CPU_PAUSE();
+                        break;
+                    }
+                    // first check if thread is sleeping
+                    kmp_flag_64 fl(&th->th.th_bar[bs_forkjoin_barrier].bb.b_go, th);
+                    if (fl.is_sleeping())
+                      fl.resume(__kmp_gtid_from_thread(th));
+                    KMP_CPU_PAUSE();

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