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() {
  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();
  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);
  }
}


void ThreadRegistry::ResumeAllThreads() {
  MonitorLocker ml(monitor_);
  ASSERT(in_rendezvous_);
  in_rendezvous_ = false;
  ml.NotifyAll();
}


void ThreadRegistry::CheckSafepointLocked() {
  int64_t last_round = -1;
  while (in_rendezvous_) {
    ASSERT(round_ >= last_round);
    if (round_ != last_round) {
      ASSERT((last_round == -1) || (round_ == (last_round + 1)));
      last_round = round_;
      // Participate in this round.
      // TODO(koda): Rename Thread::PrepareForGC and call it here?
      if (--remaining_ == 0) {
        // Ensure the organizing thread is notified.
        // TODO(koda): Use separate condition variables and plain 'Notify'.
        monitor_->NotifyAll();
      }
    }
    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