- Do not repeatedly allocate and release Monitor objects.

runtime/vm/gc_marker.cc

 // Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/gc_marker.h"
 
 #include <map>
 #include <utility>
 #include <vector>
 
@@ skipping 695 matching lines @@
           collect_code ? new(zone) SkippedCodeFunctions() : NULL;
       UnsyncMarkingVisitor mark(isolate, heap_, page_space, &marking_stack,
                                 &delay_set, skipped_code_functions);
       IterateRoots(isolate, &mark, 0, 1);
       mark.DrainMarkingStack();
       MarkingWeakVisitor mark_weak;
       IterateWeakRoots(isolate, &mark_weak);
       // All marking done; detach code, etc.
       FinalizeResultsFrom(&mark);
     } else {
-      ThreadBarrier barrier(num_tasks + 1);
+      ThreadBarrier barrier(num_tasks + 1,
+                            heap_->barrier(),
+                            heap_->barrier_done());
       // Used to coordinate draining among tasks; all start out as 'busy'.
       uintptr_t num_busy = num_tasks;
       // Phase 1: Iterate over roots and drain marking stack in tasks.
       for (intptr_t i = 0; i < num_tasks; ++i) {
         MarkTask* mark_task =
             new MarkTask(this, isolate, heap_, page_space, &marking_stack,
                          &delay_set, &barrier, collect_code,
                          i, num_tasks, &num_busy);
         ThreadPool* pool = Dart::thread_pool();
         pool->Run(mark_task);
@@ skipping 18 matching lines @@
       barrier.Exit();
     }
     delay_set.ClearReferences();
     ProcessWeakTables(page_space);
     ProcessObjectIdTable(isolate);
   }
   Epilogue(isolate, invoke_api_callbacks);
 }
 
 }  // namespace dart