8153224: Monitor deflation prolong safepoints

Add support for AsyncDeflateIdleMonitors (default true); the async deflation work is performed by the ServiceThread.

Co-authored-by: Carsten Varming <varming@gmail.com>
Reviewed-by: dcubed, rehn, rkennke, cvarming, coleenp, acorn, dholmes, eosterlund

src/hotspot/share/runtime/init.cpp

@@ -172,8 +172,12 @@ void exit_globals() {
     if (log_is_enabled(Info, monitorinflation)) {
       // The ObjectMonitor subsystem uses perf counters so
       // do this before perfMemory_exit().
-      // ObjectSynchronizer::finish_deflate_idle_monitors()'s call
-      // to audit_and_print_stats() is done at the Debug level.
+      // These other two audit_and_print_stats() calls are done at the
+      // Debug level at a safepoint:
+      // - for safepoint based deflation auditing:
+      //   ObjectSynchronizer::finish_deflate_idle_monitors()
+      // - for async deflation auditing:
+      //   ObjectSynchronizer::do_safepoint_work()
       ObjectSynchronizer::audit_and_print_stats(true /* on_exit */);
     }
     perfMemory_exit();