text: // Copyright 2016 The Chromium Authors. All rights reserved.
  // Use of this source code is governed by a BSD-style license that can be
  // found in the LICENSE file.
  
  #ifndef BASE_TASK_THREAD_POOL_THREAD_POOL_IMPL_H_
  #define BASE_TASK_THREAD_POOL_THREAD_POOL_IMPL_H_
  
  #include <memory>
  #include <vector>
  
  #include "base/base_export.h"
  #include "base/callback.h"
  #include "base/check_op.h"
  #include "base/macros.h"
  #include "base/memory/ptr_util.h"
  #include "base/memory/ref_counted.h"
  #include "base/optional.h"
  #include "base/sequence_checker.h"
  #include "base/strings/string_piece.h"
  #include "base/synchronization/atomic_flag.h"
  #include "base/task/single_thread_task_runner_thread_mode.h"
  #include "base/task/task_executor.h"
  #include "base/task/task_traits.h"
  #include "base/task/thread_pool/delayed_task_manager.h"
  #include "base/task/thread_pool/environment_config.h"
  #include "base/task/thread_pool/pooled_single_thread_task_runner_manager.h"
  #include "base/task/thread_pool/pooled_task_runner_delegate.h"
  #include "base/task/thread_pool/task_source.h"
  #include "base/task/thread_pool/task_tracker.h"
  #include "base/task/thread_pool/thread_group.h"
  #include "base/task/thread_pool/thread_group_impl.h"
  #include "base/task/thread_pool/thread_pool_instance.h"
  #include "base/updateable_sequenced_task_runner.h"
  #include "build/build_config.h"
  
  #if defined(OS_POSIX) && !defined(OS_NACL_SFI)
  #include "base/task/thread_pool/task_tracker_posix.h"
  #endif
  
  #if defined(OS_WIN)
  #include "base/win/com_init_check_hook.h"
  #endif
  
  namespace base {
  
  class Thread;
  
  namespace internal {
  
  // Default ThreadPoolInstance implementation. This class is thread-safe.
  class BASE_EXPORT ThreadPoolImpl : public ThreadPoolInstance,
                                     public TaskExecutor,
                                     public ThreadGroup::Delegate,
                                     public PooledTaskRunnerDelegate {
   public:
    using TaskTrackerImpl =
  #if defined(OS_POSIX) && !defined(OS_NACL_SFI)
        TaskTrackerPosix;
  #else
        TaskTracker;
  #endif
  
    // Creates a ThreadPoolImpl with a production TaskTracker. |histogram_label|
    // is used to label histograms. No histograms are recorded if it is empty.
    explicit ThreadPoolImpl(StringPiece histogram_label);
  
    // For testing only. Creates a ThreadPoolImpl with a custom TaskTracker.
    ThreadPoolImpl(StringPiece histogram_label,
                   std::unique_ptr<TaskTrackerImpl> task_tracker);
  
    ~ThreadPoolImpl() override;
  
    // ThreadPoolInstance:
    void Start(const ThreadPoolInstance::InitParams& init_params,
               WorkerThreadObserver* worker_thread_observer) override;
    int GetMaxConcurrentNonBlockedTasksWithTraitsDeprecated(
        const TaskTraits& traits) const override;
    void Shutdown() override;
    void FlushForTesting() override;
    void FlushAsyncForTesting(OnceClosure flush_callback) override;
    void JoinForTesting() override;
    void BeginFence() override;
    void EndFence() override;
    void BeginBestEffortFence() override;
    void EndBestEffortFence() override;
  
    // TaskExecutor:
    bool PostDelayedTask(const Location& from_here,
                         const TaskTraits& traits,
                         OnceClosure task,
                         TimeDelta delay) override;
    scoped_refptr<TaskRunner> CreateTaskRunner(const TaskTraits& traits) override;
    scoped_refptr<SequencedTaskRunner> CreateSequencedTaskRunner(
        const TaskTraits& traits) override;
    scoped_refptr<SingleThreadTaskRunner> CreateSingleThreadTaskRunner(
        const TaskTraits& traits,
        SingleThreadTaskRunnerThreadMode thread_mode) override;
  #if defined(OS_WIN)
    scoped_refptr<SingleThreadTaskRunner> CreateCOMSTATaskRunner(
        const TaskTraits& traits,
        SingleThreadTaskRunnerThreadMode thread_mode) override;
  #endif  // defined(OS_WIN)
    scoped_refptr<UpdateableSequencedTaskRunner>
    CreateUpdateableSequencedTaskRunner(const TaskTraits& traits);
  
    // PooledTaskRunnerDelegate:
    bool EnqueueJobTaskSource(scoped_refptr<JobTaskSource> task_source) override;
    void RemoveJobTaskSource(scoped_refptr<JobTaskSource> task_source) override;
    void UpdatePriority(scoped_refptr<TaskSource> task_source,
                        TaskPriority priority) override;
  
    // Returns the TimeTicks of the next task scheduled on ThreadPool (Now() if
    // immediate, nullopt if none). This is thread-safe, i.e., it's safe if tasks
    // are being posted in parallel with this call but such a situation obviously
    // results in a race as to whether this call will see the new tasks in time.
    Optional<TimeTicks> NextScheduledRunTimeForTesting() const;
  
    // Forces ripe delayed tasks to be posted (e.g. when time is mocked and
    // advances faster than the real-time delay on ServiceThread).
    void ProcessRipeDelayedTasksForTesting();
  
    // Requests that all threads started by future ThreadPoolImpls in this process
    // have a synchronous start (if |enabled|; cancels this behavior otherwise).
    // Must be called while no ThreadPoolImpls are alive in this process. This is
    // exposed here on this internal API rather than as a ThreadPoolInstance
    // configuration param because only one internal test truly needs this.
    static void SetSynchronousThreadStartForTesting(bool enabled);
  
   private:
    // Invoked after |num_fences_| or |num_best_effort_fences_| is updated. Sets
    // the CanRunPolicy in TaskTracker and wakes up workers as appropriate.
    void UpdateCanRunPolicy();
  
    // Verifies that |traits| do not have properties that are banned in ThreadPool
    // and returns |traits|, with priority set to TaskPriority::USER_BLOCKING if
    // |all_tasks_user_blocking_| is set.
    TaskTraits VerifyAndAjustIncomingTraits(TaskTraits traits) const;
  
    void ReportHeartbeatMetrics() const;
  
    const ThreadGroup* GetThreadGroupForTraits(const TaskTraits& traits) const;
  
    // ThreadGroup::Delegate:
    ThreadGroup* GetThreadGroupForTraits(const TaskTraits& traits) override;
  
    // Posts |task| to be executed by the appropriate thread group as part of
    // |sequence|. This must only be called after |task| has gone through
    // TaskTracker::WillPostTask() and after |task|'s delayed run time.
    bool PostTaskWithSequenceNow(Task task, scoped_refptr<Sequence> sequence);
  
    // PooledTaskRunnerDelegate:
    bool PostTaskWithSequence(Task task,
                              scoped_refptr<Sequence> sequence) override;
    bool ShouldYield(const TaskSource* task_source) const override;
  
    const std::unique_ptr<TaskTrackerImpl> task_tracker_;
    std::unique_ptr<Thread> service_thread_;
    DelayedTaskManager delayed_task_manager_;
    PooledSingleThreadTaskRunnerManager single_thread_task_runner_manager_;
  
    // Indicates that all tasks are handled as if they had been posted with
    // TaskPriority::USER_BLOCKING. Since this is set in Start(), it doesn't apply
    // to tasks posted before Start() or to tasks posted to TaskRunners created
    // before Start().
    //
    // TODO(fdoray): Remove after experiment. https://crbug.com/757022
    AtomicFlag all_tasks_user_blocking_;
  
    std::unique_ptr<ThreadGroup> foreground_thread_group_;
    std::unique_ptr<ThreadGroupImpl> background_thread_group_;
  
    // Whether this TaskScheduler was started. Access controlled by
    // |sequence_checker_|.
    bool started_ = false;
  
    // Whether the --disable-best-effort-tasks switch is preventing execution of
    // BEST_EFFORT tasks until shutdown.
    const bool has_disable_best_effort_switch_;
  
    // Number of fences preventing execution of tasks of any/BEST_EFFORT priority.
    // Access controlled by |sequence_checker_|.
    int num_fences_ = 0;
    int num_best_effort_fences_ = 0;
  
  #if DCHECK_IS_ON()
    // Set once JoinForTesting() has returned.
    AtomicFlag join_for_testing_returned_;
  #endif
  
  #if defined(OS_WIN) && defined(COM_INIT_CHECK_HOOK_ENABLED)
    // Provides COM initialization verification for supported builds.
    base::win::ComInitCheckHook com_init_check_hook_;
  #endif
  
    // Asserts that operations occur in sequence with Start().
    SEQUENCE_CHECKER(sequence_checker_);
  
    TrackedRefFactory<ThreadGroup::Delegate> tracked_ref_factory_;
  
    DISALLOW_COPY_AND_ASSIGN(ThreadPoolImpl);
  };
  
  }  // namespace internal
  }  // namespace base
  
  #endif  // BASE_TASK_THREAD_POOL_THREAD_POOL_IMPL_H_
  