Safepointing in GC

runtime/vm/pages.cc

 // Copyright (c) 2012, 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/pages.h"
 
 #include "platform/assert.h"
 #include "vm/compiler_stats.h"
 #include "vm/gc_marker.h"
 #include "vm/gc_sweeper.h"
 #include "vm/lockers.h"
 #include "vm/object.h"
 #include "vm/os_thread.h"
+#include "vm/thread_registry.h"
 #include "vm/verified_memory.h"
 #include "vm/virtual_memory.h"
 
 namespace dart {
 
 DEFINE_FLAG(int, heap_growth_rate, 0,
             "The max number of pages the heap can grow at a time");
 DEFINE_FLAG(int, old_gen_growth_space_ratio, 20,
             "The desired maximum percentage of free space after old gen GC");
 DEFINE_FLAG(int, old_gen_growth_time_ratio, 3,
@@ skipping 736 matching lines @@
   ASSERT(isolate == Isolate::Current());
 
   // Wait for pending tasks to complete and then account for the driver task.
   {
     MonitorLocker locker(tasks_lock());
     while (tasks() > 0) {
       locker.Wait();
     }
     set_tasks(1);
   }
+  // Ensure that all threads for this isolate are at a safepoint (either stopped
+  // or in native code). If two threads are racing at this point, the loser
+  // will continue with its collection after waiting for the winner to complete.
+  // TODO(koda): Consider moving SafepointThreads into allocation failure/retry
+  // logic to avoid needless collections.
+  isolate->thread_registry()->SafepointThreads();
 
   // Perform various cleanup that relies on no tasks interfering.
   isolate->class_table()->FreeOldTables();
 
   NoSafepointScope no_safepoints;
 
   if (FLAG_print_free_list_before_gc) {
     OS::Print("Data Freelist (before GC):\n");
     freelist_[HeapPage::kData].Print();
     OS::Print("Executable Freelist (before GC):\n");
@@ skipping 120 matching lines @@
   heap_->RecordTime(kSweepPages, mid3 - mid2);
   heap_->RecordTime(kSweepLargePages, end - mid3);
 
   if (FLAG_print_free_list_after_gc) {
     OS::Print("Data Freelist (after GC):\n");
     freelist_[HeapPage::kData].Print();
     OS::Print("Executable Freelist (after GC):\n");
     freelist_[HeapPage::kExecutable].Print();
   }
 
+  isolate->thread_registry()->ResumeAllThreads();
+
   // Done, reset the task count.
   {
     MonitorLocker ml(tasks_lock());
     set_tasks(tasks() - 1);
     ml.Notify();
   }
 }
 
 
 uword PageSpace::TryAllocateDataBumpInternal(intptr_t size,
@@ skipping 218 matching lines @@
     return 0;
   } else {
     ASSERT(total_time >= gc_time);
     int result = static_cast<int>((static_cast<double>(gc_time) /
                                    static_cast<double>(total_time)) * 100);
     return result;
   }
 }
 
 }  // namespace dart