Safepointing in GC

runtime/vm/thread_registry.cc

 // Copyright (c) 2015, 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/thread_registry.h"
 
 #include "vm/isolate.h"
 #include "vm/lockers.h"
 
 namespace dart {
 
-void ThreadRegistry::SafepointThreads() {
+SafepointId ThreadRegistry::SafepointThreads() {
   MonitorLocker ml(monitor_);
   // First wait for any older rounds that are still in progress.
   while (in_rendezvous_) {
     // Assert we are not the organizer trying to nest calls to SafepointThreads.
     ASSERT(remaining_ > 0);
     CheckSafepointLocked();
   }
   // Start a new round.
   in_rendezvous_ = true;
   ++round_;  // Overflows after 240+ years @ 10^9 safepoints per second.
-  remaining_ = CountScheduledLocked();
+  // Count the number of threads that should participate in this round.
+  remaining_ = 0;
+  for (int i = 0; i < entries_.length(); ++i) {
+    const Entry& entry = entries_[i];
+    if (entry.scheduled) {
+      // All threads that are running should participate.
+      ASSERT(IsParticipant(entry.thread));
+      ++remaining_;
+    }
+  }
   Isolate* isolate = Isolate::Current();
   // We only expect this method to be called from within the isolate itself.
   ASSERT(isolate->thread_registry() == this);
   // TODO(koda): Rename Thread::PrepareForGC and call it here?
   --remaining_;  // Exclude this thread from the count.
   // Ensure the main mutator will reach a safepoint (could be running Dart).
   if (!isolate->MutatorThreadIsCurrentThread()) {
     isolate->ScheduleInterrupts(Isolate::kVMInterrupt);
   }
   while (remaining_ > 0) {
     ml.Wait(Monitor::kNoTimeout);
   }
+  return round_;
 }
 
 
 void ThreadRegistry::ResumeAllThreads() {
   MonitorLocker ml(monitor_);
   ASSERT(in_rendezvous_);
   in_rendezvous_ = false;
   ml.NotifyAll();
 }
 
@@ skipping 16 matching lines @@
     monitor_->Wait(Monitor::kNoTimeout);
     // Note: Here, round_ is needed to detect and distinguish two cases:
     // a) The old rendezvous is still in progress, so just keep waiting, or
     // b) after ResumeAllThreads, another call to SafepointThreads was
     // made before this thread got a chance to reaquire monitor_, thus this
     // thread should (again) decrease remaining_ to indicate cooperation in
     // this new round.
   }
 }
 
-
-intptr_t ThreadRegistry::CountScheduledLocked() {
-  intptr_t count = 0;
-  for (int i = 0; i < entries_.length(); ++i) {
-    const Entry& entry = entries_[i];
-    if (entry.scheduled) {
-      ++count;
-    }
-  }
-  return count;
-}
-
 }  // namespace dart