Safepointing in GC

runtime/vm/gc_sweeper.cc

Index: runtime/vm/gc_sweeper.cc
diff --git a/runtime/vm/gc_sweeper.cc b/runtime/vm/gc_sweeper.cc
index 4cd224377b14c6ad084004ff16f48e6a541c358c..ff53575a0e5a06ef7e3d1234763c370a9836015f 100644
--- a/runtime/vm/gc_sweeper.cc
+++ b/runtime/vm/gc_sweeper.cc
@@ -96,12 +96,18 @@ class SweeperTask : public ThreadPool::Task {
               PageSpace* old_space,
               HeapPage* first,
               HeapPage* last,
-              FreeList* freelist)
+              FreeList* freelist,
+              Monitor* started_monitor,
+              bool* started_flag,
+              SafepointId pass_safepoint)
       : task_isolate_(isolate),
         old_space_(old_space),
         first_(first),
         last_(last),
-        freelist_(freelist) {
+        freelist_(freelist),
+        started_monitor_(started_monitor),
+        started_flag_(started_flag),
+        pass_safepoint_(pass_safepoint) {
     ASSERT(task_isolate_ != NULL);
     ASSERT(first_ != NULL);
     ASSERT(old_space_ != NULL);
@@ -113,7 +119,13 @@ class SweeperTask : public ThreadPool::Task {
   }
 
   virtual void Run() {
-    Thread::EnterIsolateAsHelper(task_isolate_);
+    Thread::EnterIsolateAsHelper(task_isolate_, pass_safepoint_);
+    {
+      MonitorLocker ml(started_monitor_);
+      ASSERT(!*started_flag_);
+      *started_flag_ = true;
+      ml.Notify();
+    }
     GCSweeper sweeper;
 
     HeapPage* page = first_;
@@ -153,20 +165,35 @@ class SweeperTask : public ThreadPool::Task {
   HeapPage* first_;
   HeapPage* last_;
   FreeList* freelist_;
+  Monitor* started_monitor_;
+  bool* started_flag_;
+  SafepointId pass_safepoint_;
 };
 
 
 void GCSweeper::SweepConcurrent(Isolate* isolate,
                                 HeapPage* first,
                                 HeapPage* last,
-                                FreeList* freelist) {
+                                FreeList* freelist,
+                                SafepointId pass_safepoint) {
+  Monitor started_monitor;
+  bool started_flag = false;
   SweeperTask* task =
       new SweeperTask(isolate,
                       isolate->heap()->old_space(),
                       first, last,
-                      freelist);
+                      freelist,
+                      &started_monitor,
+                      &started_flag,
+                      pass_safepoint);
   ThreadPool* pool = Dart::thread_pool();
   pool->Run(task);
+  {
+    MonitorLocker ml(&started_monitor);

[Ivan Posva, 2015/08/19 08:00:04]

I don't expect it to be needed to wait for the sweeper threads to start running
before the marker can make further progress.

+    while (!started_flag) {
+      ml.Wait();
+    }
+  }
 }
 
 }  // namespace dart