ParallelMarking.h - mozsearch

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/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*-

 * vim: set ts=8 sts=2 et sw=2 tw=80:

 * This Source Code Form is subject to the terms of the Mozilla Public

 * License, v. 2.0. If a copy of the MPL was not distributed with this

 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

#ifndef gc_ParallelMarking_h

#define gc_ParallelMarking_h

#include "mozilla/Atomics.h"

#include "mozilla/DoublyLinkedList.h"

#include "mozilla/TimeStamp.h"

#include "gc/GCMarker.h"

#include "gc/GCParallelTask.h"

#include "js/HeapAPI.h"

#include "js/SliceBudget.h"

#include "threading/ConditionVariable.h"

#include "threading/ProtectedData.h"

namespace js {

class AutoLockHelperThreadState;

namespace gc {

class ParallelMarkTask;

// Per-runtime parallel marking state.

//

// This class is used on the main thread and coordinates parallel marking using

// several helper threads running ParallelMarkTasks.

//

// This uses a work-requesting approach. Threads mark until they run out of

// work and then add themselves to a list of waiting tasks and block. Running

// tasks with enough work may donate work to a waiting task and resume it.

class MOZ_STACK_CLASS ParallelMarker {

 public:

  explicit ParallelMarker(GCRuntime* gc);

  bool mark(JS::SliceBudget& sliceBudget);

  using AtomicCount = mozilla::Atomic<uint32_t, mozilla::Relaxed>;

  AtomicCount& waitingTaskCountRef() { return waitingTaskCount; }

  bool hasWaitingTasks() { return waitingTaskCount != 0; }

  void donateWorkFrom(GCMarker* src);

 private:

  bool markOneColor(MarkColor color, JS::SliceBudget& sliceBudget);

  bool hasWork(MarkColor color) const;

  void addTask(ParallelMarkTask* task, const AutoLockHelperThreadState& lock);

  void addTaskToWaitingList(ParallelMarkTask* task,

                            const AutoLockHelperThreadState& lock);

#ifdef DEBUG

  bool isTaskInWaitingList(const ParallelMarkTask* task,

                           const AutoLockHelperThreadState& lock) const;

#endif

  bool hasActiveTasks(const AutoLockHelperThreadState& lock) const {

    return activeTasks;

  void incActiveTasks(ParallelMarkTask* task,

                      const AutoLockHelperThreadState& lock);

  void decActiveTasks(ParallelMarkTask* task,

                      const AutoLockHelperThreadState& lock);

  size_t workerCount() const;

  friend class ParallelMarkTask;

  GCRuntime* const gc;

  using ParallelMarkTaskList = mozilla::DoublyLinkedList<ParallelMarkTask>;

  HelperThreadLockData<ParallelMarkTaskList> waitingTasks;

  AtomicCount waitingTaskCount;

  HelperThreadLockData<size_t> activeTasks;

};

// A helper thread task that performs parallel marking.

class alignas(TypicalCacheLineSize) ParallelMarkTask

    : public GCParallelTask,

      public mozilla::DoublyLinkedListElement<ParallelMarkTask> {

 public:

  friend class ParallelMarker;

  ParallelMarkTask(ParallelMarker* pm, GCMarker* marker, MarkColor color,

                   const JS::SliceBudget& budget);

  ~ParallelMarkTask();

  void run(AutoLockHelperThreadState& lock) override;

  void recordDuration() override;

 private:

  bool tryMarking(AutoLockHelperThreadState& lock);

  bool requestWork(AutoLockHelperThreadState& lock);

  void waitUntilResumed(AutoLockHelperThreadState& lock);

  void resume();

  void resumeOnFinish(const AutoLockHelperThreadState& lock);

  bool hasWork() const;

  // The following fields are only accessed by the marker thread:

  ParallelMarker* const pm;

  GCMarker* const marker;

  AutoSetMarkColor color;

  JS::SliceBudget budget;

  ConditionVariable resumed;

  HelperThreadLockData<bool> isWaiting;

  // Length of time this task spent blocked waiting for work.

  MainThreadOrGCTaskData<mozilla::TimeDuration> markTime;

  MainThreadOrGCTaskData<mozilla::TimeDuration> waitTime;

};

}  // namespace gc

}  // namespace js

#endif /* gc_ParallelMarking_h */