RFR(xxs): 8209495: NMethodSweeper::sweep_code_cache cause severe delays

[Robbin Ehn]

Hi please review,

Issue:
https://bugs.openjdk.java.net/browse/JDK-8209495

Code:
diff -r 875999ffe38d src/hotspot/share/runtime/sweeper.cpp
--- a/src/hotspot/share/runtime/sweeper.cpp	Wed Oct 31 14:07:15 2018 +0100
+++ b/src/hotspot/share/runtime/sweeper.cpp	Wed Oct 31 15:28:39 2018 +0100
@@ -390,1 +390,2 @@
-  if (SafepointSynchronize::is_synchronizing()) {
+  JavaThread* thread = JavaThread::current();
+  if (SafepointMechanism::poll(thread)) {
@@ -396,1 +396,0 @@
-    JavaThread* thread = JavaThread::current();


Since we only do the ThreadBlockInVM if there is a safepoint,
this have a bad effect on handshakes.

RunThese30M works with much lower timeout, tenths of millis.

Thanks, Robbin