8040245: G1: VM hangs during shutdown

Summary: temporarily disable the shutdown of the concurrent GC threads introduced in JDK-8037112
Reviewed-by: brutisso, tschatzl, jmasa

src/share/vm/gc_implementation/g1/g1CollectedHeap.cpp

@@ -2186,6 +2186,12 @@ jint G1CollectedHeap::initialize() {
 }
 
 void G1CollectedHeap::stop() {
+#if 0
+  // Stopping concurrent worker threads is currently disabled until
+  // some bugs in concurrent mark has been resolve. Without fixing
+  // those bugs first we risk haning during VM exit when trying to
+  // stop these threads.
+
   // Abort any ongoing concurrent root region scanning and stop all
   // concurrent threads. We do this to make sure these threads do
   // not continue to execute and access resources (e.g. gclog_or_tty)
@@ -2193,6 +2199,7 @@ void G1CollectedHeap::stop() {
   _cm->root_regions()->abort();
   _cm->root_regions()->wait_until_scan_finished();
   stop_conc_gc_threads();
+#endif
 }
 
 size_t G1CollectedHeap::conservative_max_heap_alignment() {