7051430: CMS: ongoing CMS cycle should terminate abruptly to allow prompt JVM termination at exit

Summary: It turns out that there is no need to explicitly stop CMS since the JVM is taken down at a terminal safepoint during which CMS threads are (terminally) inactive. This  will need to be revised if and when we evolve in the future to a point where we allow JVM reincarnation in the same process, but those changes will be much more sweeping than just terminating CMS threads. The unused ::stop() methods will be removed in a separate CR. Also include in this CR is the fix for a small typo in the spelling of UseGCLogFileRotation in a message in arguments.cpp, brought to our attention by Rainer Jung and reviewed by minqi.
Reviewed-by: johnc, jwilhelm

src/share/vm/runtime/arguments.cpp

@@ -1690,7 +1690,7 @@ void check_gclog_consistency() {
         (NumberOfGCLogFiles == 0)  ||
         (GCLogFileSize == 0)) {
       jio_fprintf(defaultStream::output_stream(),
-                  "To enable GC log rotation, use -Xloggc:<filename> -XX:+UseGCLogRotaion -XX:NumberOfGCLogFiles=<num_of_files> -XX:GCLogFileSize=<num_of_size>\n"
+                  "To enable GC log rotation, use -Xloggc:<filename> -XX:+UseGCLogFileRotation -XX:NumberOfGCLogFiles=<num_of_files> -XX:GCLogFileSize=<num_of_size>\n"
                   "where num_of_file > 0 and num_of_size > 0\n"
                   "GC log rotation is turned off\n");
       UseGCLogFileRotation = false;

src/share/vm/runtime/java.cpp

@@ -468,12 +468,10 @@ void before_exit(JavaThread * thread) {
   StatSampler::disengage();
   StatSampler::destroy();
 
-#ifndef SERIALGC
-  // stop CMS threads
-  if (UseConcMarkSweepGC) {
-    ConcurrentMarkSweepThread::stop();
-  }
-#endif // SERIALGC
+  // We do not need to explicitly stop concurrent GC threads because the
+  // JVM will be taken down at a safepoint when such threads are inactive --
+  // except for some concurrent G1 threads, see (comment in)
+  // Threads::destroy_vm().
 
   // Print GC/heap related information.
   if (PrintGCDetails) {

src/share/vm/runtime/thread.cpp

@@ -3698,6 +3698,14 @@ bool Threads::destroy_vm() {
     // heap is unparseable if they are caught. Grab the Heap_lock
     // to prevent this. The GC vm_operations will not be able to
     // queue until after the vm thread is dead.
+    // After this point, we'll never emerge out of the safepoint before
+    // the VM exits, so concurrent GC threads do not need to be explicitly
+    // stopped; they remain inactive until the process exits.
+    // Note: some concurrent G1 threads may be running during a safepoint,
+    // but these will not be accessing the heap, just some G1-specific side
+    // data structures that are not accessed by any other threads but them
+    // after this point in a terminal safepoint.
+
     MutexLocker ml(Heap_lock);
 
     VMThread::wait_for_vm_thread_exit();