Instrument callers of Semaphore::Signal to help with investigation of

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/base/sys-info.h"
 #include "src/code-stubs.h"
@@ skipping 462 matching lines @@
     DCHECK_GE(space_to_start_, FIRST_PAGED_SPACE);
     DCHECK_LE(space_to_start_, LAST_PAGED_SPACE);
     const int offset = space_to_start_ - FIRST_PAGED_SPACE;
     const int num_spaces = LAST_PAGED_SPACE - FIRST_PAGED_SPACE + 1;
     for (int i = 0; i < num_spaces; i++) {
       const int space_id = FIRST_PAGED_SPACE + ((i + offset) % num_spaces);
       DCHECK_GE(space_id, FIRST_PAGED_SPACE);
       DCHECK_LE(space_id, LAST_PAGED_SPACE);
       sweeper_->ParallelSweepSpace(static_cast<AllocationSpace>(space_id), 0);
     }
-    pending_sweeper_tasks_->Signal();
+    pending_sweeper_tasks_->Signal("SweeperTask::Run");
   }
 
   Sweeper* sweeper_;
   base::Semaphore* pending_sweeper_tasks_;
   AllocationSpace space_to_start_;
 
   DISALLOW_COPY_AND_ASSIGN(SweeperTask);
 };
 
 void MarkCompactCollector::Sweeper::StartSweeping() {
@@ skipping 84 matching lines @@
     VerifyEvacuation(heap_);
   }
 #endif
 }
 
 bool MarkCompactCollector::Sweeper::IsSweepingCompleted() {
   if (!pending_sweeper_tasks_semaphore_.WaitFor(
           base::TimeDelta::FromSeconds(0))) {
     return false;
   }
-  pending_sweeper_tasks_semaphore_.Signal();
+  pending_sweeper_tasks_semaphore_.Signal("Sweeper::IsSweepingCompleted");
   return true;
 }
 
 void Marking::TransferMark(Heap* heap, Address old_start, Address new_start) {
   // This is only used when resizing an object.
   DCHECK(MemoryChunk::FromAddress(old_start) ==
          MemoryChunk::FromAddress(new_start));
 
   if (!heap->incremental_marking()->IsMarking() ||
       Page::FromAddress(old_start)->IsFlagSet(Page::BLACK_PAGE))
@@ skipping 3348 matching lines @@
     MarkBit mark_bit = Marking::MarkBitFrom(host);
     if (Marking::IsBlack(mark_bit)) {
       RelocInfo rinfo(isolate(), pc, RelocInfo::CODE_TARGET, 0, host);
       RecordRelocSlot(host, &rinfo, target);
     }
   }
 }
 
 }  // namespace internal
 }  // namespace v8