Make number of available threads isolate-dependent and expose it to ResourceConstraints.

src/mark-compact.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 546 matching lines @@
     mark_bit.Clear();
     mark_bit.Next().Clear();
     Page::FromAddress(obj->address())->ResetProgressBar();
     Page::FromAddress(obj->address())->ResetLiveBytes();
   }
 }
 
 
 void MarkCompactCollector::StartSweeperThreads() {
   sweeping_pending_ = true;
-  for (int i = 0; i < FLAG_sweeper_threads; i++) {
+  for (int i = 0; i < isolate()->num_sweeper_threads(); i++) {
     isolate()->sweeper_threads()[i]->StartSweeping();
   }
 }
 
 
 void MarkCompactCollector::WaitUntilSweepingCompleted() {
   ASSERT(sweeping_pending_ == true);
-  for (int i = 0; i < FLAG_sweeper_threads; i++) {
+  for (int i = 0; i < isolate()->num_sweeper_threads(); i++) {
     isolate()->sweeper_threads()[i]->WaitForSweeperThread();
   }
   sweeping_pending_ = false;
   StealMemoryFromSweeperThreads(heap()->paged_space(OLD_DATA_SPACE));
   StealMemoryFromSweeperThreads(heap()->paged_space(OLD_POINTER_SPACE));
   heap()->paged_space(OLD_DATA_SPACE)->ResetUnsweptFreeBytes();
   heap()->paged_space(OLD_POINTER_SPACE)->ResetUnsweptFreeBytes();
 }
 
 
 intptr_t MarkCompactCollector::
              StealMemoryFromSweeperThreads(PagedSpace* space) {
   intptr_t freed_bytes = 0;
-  for (int i = 0; i < FLAG_sweeper_threads; i++) {
+  for (int i = 0; i < isolate()->num_sweeper_threads(); i++) {
     freed_bytes += isolate()->sweeper_threads()[i]->StealMemory(space);
   }
   space->AddToAccountingStats(freed_bytes);
   space->DecrementUnsweptFreeBytes(freed_bytes);
   return freed_bytes;
 }
 
 
 bool MarkCompactCollector::AreSweeperThreadsActivated() {
   return isolate()->sweeper_threads() != NULL;
@@ skipping 3494 matching lines @@
 }
 
 
 void MarkCompactCollector::SweepSpaces() {
   GCTracer::Scope gc_scope(tracer_, GCTracer::Scope::MC_SWEEP);
 #ifdef DEBUG
   state_ = SWEEP_SPACES;
 #endif
   SweeperType how_to_sweep =
       FLAG_lazy_sweeping ? LAZY_CONSERVATIVE : CONSERVATIVE;
-  if (FLAG_parallel_sweeping) how_to_sweep = PARALLEL_CONSERVATIVE;
-  if (FLAG_concurrent_sweeping) how_to_sweep = CONCURRENT_CONSERVATIVE;
+  if (isolate()->num_sweeper_threads() > 0) {
+    if (FLAG_parallel_sweeping) how_to_sweep = PARALLEL_CONSERVATIVE;
+    if (FLAG_concurrent_sweeping) how_to_sweep = CONCURRENT_CONSERVATIVE;
+  }
   if (FLAG_expose_gc) how_to_sweep = CONSERVATIVE;
   if (sweep_precisely_) how_to_sweep = PRECISE;
 
   // Unlink evacuation candidates before sweeper threads access the list of
   // pages to avoid race condition.
   UnlinkEvacuationCandidates();
 
   // Noncompacting collections simply sweep the spaces to clear the mark
   // bits and free the nonlive blocks (for old and map spaces).  We sweep
   // the map space last because freeing non-live maps overwrites them and
@@ skipping 235 matching lines @@
   while (buffer != NULL) {
     SlotsBuffer* next_buffer = buffer->next();
     DeallocateBuffer(buffer);
     buffer = next_buffer;
   }
   *buffer_address = NULL;
 }
 
 
 } }  // namespace v8::internal