[8] RFR: Cherry-pick JDK-8231201: hs_err should print coalesced safepoint operations in Events section

[Aleksey Shipilev]

Looking at hs_errs from Alexander, I suspect there are more VM operations happening than meets the
eye. See for example:

Event: 749.332 Executing VM operation: FindDeadlocks
Event: 749.333 Pause Init Update Refs
Event: 751.083 Pause Init Update Refs done
Event: 751.083 Executing VM operation: FindDeadlocks done

Where's the "Executing VM operation: ShenandoahInitUpdateRefs"? The answer is here:
  https://bugs.openjdk.java.net/browse/JDK-8231201

I requested the jdk8u backport here:
  https://mail.openjdk.java.net/pipermail/jdk8u-dev/2019-November/010552.html

...but it would be a while before it lands in sh/jdk8. So, let's cherry-pick it:

diff -r e8582ad276a2 src/share/vm/runtime/vmThread.cpp
--- a/src/share/vm/runtime/vmThread.cpp Mon Nov 04 12:25:21 2019 +0100
+++ b/src/share/vm/runtime/vmThread.cpp Mon Nov 04 19:23:12 2019 +0100
@@ -505,10 +505,11 @@
         // the queue until there are none left
         do {
           _cur_vm_operation = safepoint_ops;
           if (_cur_vm_operation != NULL) {
             do {
+              EventMark em("Executing coalesced VM operation: %s", _cur_vm_operation->name());
               // evaluate_operation deletes the op object so we have
               // to grab the next op now
               VM_Operation* next = _cur_vm_operation->next();
               _vm_queue->set_drain_list(next);
               evaluate_operation(_cur_vm_operation);

Testing: hotspot_gc_shenandoah

-- 
Thanks,
-Aleksey