Prevent monitor thread creation when KMP_BLOCKTIME="infinite"

[jlpeyton]

Summary

When users sets envirable KMP_BLOCKTIME to "infinite" (the time one busy-waits at barrieres, etc.), the monitor thread is not useful and can be ignored. This change prevents the creation of the monitor thread when the users sets KMP_BLOCKTIME to "infinite".

[tlwilmar]

LGTM

runtime/src/z_Linux_util.c

 __kmp_create_monitor( kmp_info_t *th )
 {
     pthread_t           handle;
     pthread_attr_t      thread_attr;
     size_t              size;
     int                 status;
     int                 auto_adj_size = FALSE;
 
+    if( __kmp_dflt_blocktime == KMP_MAX_BLOCKTIME ) {
+        // We don't need monitor thread in case of MAX_BLOCKTIME
+        KA_TRACE( 10, ("__kmp_create_monitor: skipping monitor thread because of MAX blocktime\n" ) );
+        th->th.th_info.ds.ds_tid  = 0; // this makes reap_monitor no-op
+        th->th.th_info.ds.ds_gtid = 0;
+        return;
+    }
     KA_TRACE( 10, ("__kmp_create_monitor: try to create monitor\n" ) );
 
     KMP_MB();       /* Flush all pending memory write invalidates.  */
 
     th->th.th_info.ds.ds_tid  = KMP_GTID_MONITOR;
     th->th.th_info.ds.ds_gtid = KMP_GTID_MONITOR;
     #if KMP_REAL_TIME_FIX
         TCW_4( __kmp_global.g.g_time.dt.t_value, -1 ); // Will use it for synchronization a bit later.
__kmp_reap_monitor( kmp_info_t *th )
     KA_TRACE( 10, ("__kmp_reap_monitor: try to reap monitor thread with handle %#.8lx\n",
                    th->th.th_info.ds.ds_thread ) );
 
     // If monitor has been created, its tid and gtid should be KMP_GTID_MONITOR.
     // If both tid and gtid are 0, it means the monitor did not ever start.
     // If both tid and gtid are KMP_GTID_DNE, the monitor has been shut down.
     KMP_DEBUG_ASSERT( th->th.th_info.ds.ds_tid == th->th.th_info.ds.ds_gtid );
     if ( th->th.th_info.ds.ds_gtid != KMP_GTID_MONITOR ) {
+        KA_TRACE( 10, ("__kmp_reap_monitor: monitor did not start, returning\n") );
         return;
     }; // if
 
     KMP_MB();       /* Flush all pending memory write invalidates.  */
 
 
     /* First, check to see whether the monitor thread exists.  This could prevent a hang,
        but if the monitor dies after the pthread_kill call and before the pthread_join

runtime/src/z_Windows_NT_util.c

 
 void
 __kmp_create_monitor( kmp_info_t *th )
 {
     kmp_thread_t        handle;
     DWORD               idThread;
     int                 ideal, new_ideal;
 
+    if( __kmp_dflt_blocktime == KMP_MAX_BLOCKTIME ) {
+        // We don't need monitor thread in case of MAX_BLOCKTIME
+        KA_TRACE( 10, ("__kmp_create_monitor: skipping monitor thread because of MAX blocktime\n" ) );
+        th->th.th_info.ds.ds_tid  = 0; // this makes reap_monitor no-op
+        th->th.th_info.ds.ds_gtid = 0;
+        TCW_4( __kmp_init_monitor, 2 ); // Signal to stop waiting for monitor creation
+        return;
+    }
     KA_TRACE( 10, ("__kmp_create_monitor: try to create monitor\n" ) );
 
     KMP_MB();       /* Flush all pending memory write invalidates.  */
 
     __kmp_monitor_ev = CreateEvent( NULL, TRUE, FALSE, NULL );
     if ( __kmp_monitor_ev == NULL ) {
         DWORD error = GetLastError();
         __kmp_msg(
__kmp_reap_monitor( kmp_info_t *th )
     KA_TRACE( 10, ("__kmp_reap_monitor: try to reap %p\n",
                    (void *) th->th.th_info.ds.ds_thread ) );
 
     // If monitor has been created, its tid and gtid should be KMP_GTID_MONITOR.
     // If both tid and gtid are 0, it means the monitor did not ever start.
     // If both tid and gtid are KMP_GTID_DNE, the monitor has been shut down.
     KMP_DEBUG_ASSERT( th->th.th_info.ds.ds_tid == th->th.th_info.ds.ds_gtid );
     if ( th->th.th_info.ds.ds_gtid != KMP_GTID_MONITOR ) {
+        KA_TRACE( 10, ("__kmp_reap_monitor: monitor did not start, returning\n") );
         return;
     }; // if
 
     KMP_MB();       /* Flush all pending memory write invalidates.  */
 
     status = SetEvent( __kmp_monitor_ev );
     if ( status == FALSE ) {
         DWORD error = GetLastError();