[heap] Adjust condition for AdjustLiveBytes to avoid concurrent access w/ sweeper

src/heap/mark-compact.cc

Index: src/heap/mark-compact.cc
diff --git a/src/heap/mark-compact.cc b/src/heap/mark-compact.cc
index 6025e298ea560eec70f0782fbe18fb2bb4f01a46..9ba2d5a3406526dc3d11faf40d68ef694c89a241 100644
--- a/src/heap/mark-compact.cc
+++ b/src/heap/mark-compact.cc
@@ -3982,6 +3982,7 @@ void MarkCompactCollector::SweepSpaces() {
   MoveEvacuationCandidatesToEndOfPagesList();
 
   {
+    sweeping_in_progress_ = true;

[Michael Lippautz, 2016/01/11 09:49:56]

This is not really needed as we sweep on the main thread (thus cannot have any
concurrent access with the markbits).

However, for correctness (of sweeping_in_progress()) we should indicate that we
are already sweeping?

[Hannes Payer (out of office), 2016/01/11 12:28:40]

Acknowledged.

     {
       GCTracer::Scope sweep_scope(heap()->tracer(),
                                   GCTracer::Scope::MC_SWEEP_OLD);
@@ -3997,7 +3998,6 @@ void MarkCompactCollector::SweepSpaces() {
                                   GCTracer::Scope::MC_SWEEP_MAP);
       StartSweepSpace(heap()->map_space());
     }
-    sweeping_in_progress_ = true;
     if (FLAG_concurrent_sweeping) {
       StartSweeperThreads();
     }