Add safepointing to the GC

BUG=
R=iposva@google.com

Review URL: https://codereview.chromium.org//1292353004 .

runtime/vm/gc_sweeper.cc

@@ -10,6 +10,7 @@
 #include "vm/lockers.h"
 #include "vm/pages.h"
 #include "vm/thread_pool.h"
+#include "vm/thread_registry.h"
 
 namespace dart {
 
@@ -120,6 +121,7 @@ class SweeperTask : public ThreadPool::Task {
     HeapPage* prev_page = NULL;
 
     while (page != NULL) {
+      task_isolate_->thread_registry()->CheckSafepoint();
       HeapPage* next_page = page->next();
       ASSERT(page->type() == HeapPage::kData);
       bool page_in_use = sweeper.SweepPage(page, freelist_, false);

runtime/vm/pages.cc

@@ -11,6 +11,7 @@
 #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"
 
@@ -767,6 +768,12 @@ void PageSpace::MarkSweep(bool invoke_api_callbacks) {
     }
     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();
@@ -907,6 +914,8 @@ void PageSpace::MarkSweep(bool invoke_api_callbacks) {
     freelist_[HeapPage::kExecutable].Print();
   }
 
+  isolate->thread_registry()->ResumeAllThreads();
+
   // Done, reset the task count.
   {
     MonitorLocker ml(tasks_lock());

runtime/vm/scavenger.cc

@@ -16,6 +16,7 @@
 #include "vm/object_id_ring.h"
 #include "vm/stack_frame.h"
 #include "vm/store_buffer.h"
+#include "vm/thread_registry.h"
 #include "vm/verified_memory.h"
 #include "vm/verifier.h"
 #include "vm/visitor.h"
@@ -799,10 +800,18 @@ void Scavenger::Scavenge() {
 
 
 void Scavenger::Scavenge(bool invoke_api_callbacks) {
+  Isolate* isolate = heap_->isolate();
+  // 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 scavenge 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();
+
   // Scavenging is not reentrant. Make sure that is the case.
   ASSERT(!scavenging_);
   scavenging_ = true;
-  Isolate* isolate = heap_->isolate();
+
   PageSpace* page_space = heap_->old_space();
   NoSafepointScope no_safepoints;
 
@@ -861,6 +870,8 @@ void Scavenger::Scavenge(bool invoke_api_callbacks) {
   // Done scavenging. Reset the marker.
   ASSERT(scavenging_);
   scavenging_ = false;
+
+  isolate->thread_registry()->ResumeAllThreads();
 }
 
 

runtime/vm/thread_test.cc

@@ -498,12 +498,12 @@ TEST_CASE(HelperAllocAndGC) {
   Thread::PrepareForGC();
   Dart::thread_pool()->Run(new AllocAndGCTask(isolate, &done_monitor, &done));
   {
-    // Manually wait.
-    // TODO(koda): Replace with execution of Dart and/or VM code when GC
-    // actually safepoints everything.
-    MonitorLocker ml(&done_monitor);
-    while (!done) {
-      ml.Wait();
+    while (true) {
+      isolate->thread_registry()->CheckSafepoint();
+      MonitorLocker ml(&done_monitor);
+      if (done) {
+        break;
+      }
     }
   }
 }