Safepointing in GC

runtime/vm/scavenger.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/scavenger.h"
 
 #include <algorithm>
 #include <map>
 #include <utility>
 
 #include "vm/dart.h"
 #include "vm/dart_api_state.h"
 #include "vm/isolate.h"
 #include "vm/lockers.h"
 #include "vm/object.h"
 #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"
 #include "vm/weak_table.h"
 
 namespace dart {
 
 DEFINE_FLAG(int, early_tenuring_threshold, 66,
             "When more than this percentage of promotion candidates survive, "
             "promote all survivors of next scavenge.");
@@ skipping 767 matching lines @@
   // the API callbacks should be invoked.
   Scavenge(false);
 }
 
 
 void Scavenger::Scavenge(bool invoke_api_callbacks) {
   // Scavenging is not reentrant. Make sure that is the case.
   ASSERT(!scavenging_);
   scavenging_ = true;
   Isolate* isolate = heap_->isolate();
+
+  isolate->thread_registry()->SafepointThreads();

[Ivan Posva, 2015/08/25 23:27:15]

ditto about the comment.

Also please explain what will happen if two different threads decide to race for
triggering a GC at the same time.

[koda, 2015/08/26 01:09:14]

Done.

Added TODO about avoiding the possibility of redundant collections by moving
safepointing into allocation failure/retry logic.

+
   PageSpace* page_space = heap_->old_space();
   NoSafepointScope no_safepoints;
 
   // TODO(koda): Make verification more compatible with concurrent sweep.
   if (FLAG_verify_before_gc && !FLAG_concurrent_sweep) {
     OS::PrintErr("Verifying before Scavenge...");
     heap_->Verify(kForbidMarked);
     OS::PrintErr(" done.\n");
   }
 
@@ skipping 35 matching lines @@
   }
   Epilogue(isolate, from, invoke_api_callbacks);
 
   // TODO(koda): Make verification more compatible with concurrent sweep.
   if (FLAG_verify_after_gc && !FLAG_concurrent_sweep) {
     OS::PrintErr("Verifying after Scavenge...");
     heap_->Verify(kForbidMarked);
     OS::PrintErr(" done.\n");
   }
 
+  isolate->thread_registry()->ResumeAllThreads();
+
   // Done scavenging. Reset the marker.
   ASSERT(scavenging_);
   scavenging_ = false;
 }
 
 
 void Scavenger::WriteProtect(bool read_only) {
   ASSERT(!scavenging_);
   to_->WriteProtect(read_only);
 }
@@ skipping 31 matching lines @@
 }
 
 
 void Scavenger::FreeExternal(intptr_t size) {
   ASSERT(size >= 0);
   external_size_ -= size;
   ASSERT(external_size_ >= 0);
 }
 
 }  // namespace dart