[heap] Fix waiting for parallel tasks

src/heap/mark-compact.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/heap/mark-compact.h"
 
 #include "src/base/atomicops.h"
 #include "src/base/bits.h"
 #include "src/code-stubs.h"
 #include "src/compilation-cache.h"
@@ skipping 3446 matching lines @@
             abandoned_pages, num_pages);
       } else {
         PrintF("  Compacted %d pages\n", num_pages);
       }
     }
   }
 }
 
 
 void MarkCompactCollector::WaitUntilCompactionCompleted() {
-  while (concurrent_compaction_tasks_active_-- > 0) {
+  while (concurrent_compaction_tasks_active_ > 0) {
     pending_compaction_tasks_semaphore_.Wait();
+    concurrent_compaction_tasks_active_--;
   }
   parallel_compaction_in_progress_ = false;
 }
 
 
 void MarkCompactCollector::EvacuatePages(
     CompactionSpaceCollection* compaction_spaces) {
   for (int i = 0; i < evacuation_candidates_.length(); i++) {
     Page* p = evacuation_candidates_[i];
     DCHECK(p->IsEvacuationCandidate() ||
@@ skipping 1090 matching lines @@
     MarkBit mark_bit = Marking::MarkBitFrom(host);
     if (Marking::IsBlack(mark_bit)) {
       RelocInfo rinfo(pc, RelocInfo::CODE_TARGET, 0, host);
       RecordRelocSlot(&rinfo, target);
     }
   }
 }
 
 }  // namespace internal
 }  // namespace v8