Introduce SchedulerSingleThreadTaskRunnerManager

base/task_scheduler/scheduler_single_thread_task_runner_manager.cc

+// Copyright 2017 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.
+
+#include "base/task_scheduler/scheduler_single_thread_task_runner_manager.h"
+
+#include <algorithm>
+#include <memory>
+#include <string>
+
+#include "base/bind.h"
+#include "base/callback.h"
+#include "base/memory/ptr_util.h"
+#include "base/single_thread_task_runner.h"
+#include "base/strings/stringprintf.h"
+#include "base/synchronization/atomic_flag.h"
+#include "base/task_scheduler/delayed_task_manager.h"
+#include "base/task_scheduler/scheduler_worker.h"
+#include "base/task_scheduler/sequence.h"
+#include "base/task_scheduler/task.h"
+#include "base/task_scheduler/task_tracker.h"
+#include "base/task_scheduler/task_traits.h"
+#include "base/threading/platform_thread.h"
+#include "base/time/time.h"
+
+namespace base {
+namespace internal {
+
+namespace {
+
+// Allows for checking the PlatformThread::CurrentRef() against a set
+// PlatformThreadRef atomically without using locks.
+class AtomicThreadRefChecker {
+ public:
+  AtomicThreadRefChecker() = default;
+  ~AtomicThreadRefChecker() = default;
+
+  void Set() {
+    thread_ref_ = PlatformThread::CurrentRef();
+    is_set_.Set();
+  }
+
+  bool IsCurrentThreadSameAsSetThread() {
+    return is_set_.IsSet() && thread_ref_ == PlatformThread::CurrentRef();
+  }
+
+ private:
+  AtomicFlag is_set_;
+  PlatformThreadRef thread_ref_;
+
+  DISALLOW_COPY_AND_ASSIGN(AtomicThreadRefChecker);
+};
+
+class SchedulerWorkerDelegate : public SchedulerWorker::Delegate {
+ public:
+  SchedulerWorkerDelegate(const std::string& thread_name)
+      : thread_name_(thread_name) {}
+
+  // SchedulerWorker::Delegate:
+  void OnMainEntry(SchedulerWorker* worker) override {
+    thread_ref_checker_.Set();
+    PlatformThread::SetName(thread_name_);
+  }
+
+  scoped_refptr<Sequence> GetWork(SchedulerWorker* worker) override {
+    AutoSchedulerLock auto_lock(sequence_lock_);
+    bool has_work = has_work_;
+    has_work_ = false;
+    return has_work ? sequence_ : nullptr;
+  }
+
+  void DidRunTask() override {}
+
+  void ReEnqueueSequence(scoped_refptr<Sequence> sequence) override {
+    AutoSchedulerLock auto_lock(sequence_lock_);
+    // We've shut down, so no-op this work request. Any sequence cleanup will
+    // occur in the caller's context.
+    if (!sequence_)
+      return;
+
+    DCHECK_EQ(sequence, sequence_);
+    has_work_ = true;
+  }
+
+  TimeDelta GetSleepTimeout() override { return TimeDelta::Max(); }
+
+  bool CanDetach(SchedulerWorker* worker) override { return false; }
+
+  void OnDetach() override { NOTREACHED(); }
+
+  bool RunsTasksOnCurrentThread() {
+    // We check the thread ref instead of the sequence for the benefit of COM
+    // callbacks which may execute without a sequence context.
+    return thread_ref_checker_.IsCurrentThreadSameAsSetThread();
+  }
+
+  void OnMainExit() override {
+    // Move |sequence_| to |local_sequence| so that if we have the last
+    // reference to the sequence we don't destroy it (and its tasks) within
+    // |sequence_lock_|.
+    scoped_refptr<Sequence> local_sequence;
+    {
+      AutoSchedulerLock auto_lock(sequence_lock_);
+      // To reclaim skipped tasks on shutdown, we null out the sequence to allow
+      // the tasks to destroy themselves.
+      local_sequence = std::move(sequence_);
+    }
+  }
+
+  // SchedulerWorkerDelegate:
+
+  // Consumers should release their sequence reference as soon as possible to
+  // ensure timely cleanup for general shutdown.
+  scoped_refptr<Sequence> sequence() {
+    AutoSchedulerLock auto_lock(sequence_lock_);
+    return sequence_;
+  }
+
+ private:
+  const std::string thread_name_;
+
+  // Synchronizes access to |sequence_| and |has_work_|.
+  SchedulerLock sequence_lock_;
+  scoped_refptr<Sequence> sequence_ = new Sequence;
+  bool has_work_ = false;
+
+  AtomicThreadRefChecker thread_ref_checker_;
+
+  DISALLOW_COPY_AND_ASSIGN(SchedulerWorkerDelegate);
+};
+
+}  // namespace
+
+class SchedulerSingleThreadTaskRunnerManager::SchedulerSingleThreadTaskRunner
+    : public SingleThreadTaskRunner {
+ public:
+  // Constructs a SchedulerSingleThreadTaskRunner that indirectly controls the
+  // lifetime of a dedicated |worker| for |traits|.
+  SchedulerSingleThreadTaskRunner(
+      SchedulerSingleThreadTaskRunnerManager* const outer,
+      const TaskTraits& traits,
+      SchedulerWorker* worker)
+      : outer_(outer), traits_(traits), worker_(worker) {
+    DCHECK(outer_);
+    DCHECK(worker_);
+  }
+
+  // SingleThreadTaskRunner:
+  bool PostDelayedTask(const tracked_objects::Location& from_here,
+                       const Closure& closure,
+                       TimeDelta delay) override {
+    auto task = MakeUnique<Task>(from_here, closure, traits_, delay);
+    task->single_thread_task_runner_ref = this;
+
+    if (!outer_->task_tracker_->WillPostTask(task.get()))
+      return false;
+
+    if (task->delayed_run_time.is_null()) {
+      PostTaskNow(std::move(task));
+    } else {
+      outer_->delayed_task_manager_->AddDelayedTask(
+          std::move(task), Bind(&SchedulerSingleThreadTaskRunner::PostTaskNow,
+                                Unretained(this)));
+    }
+    return true;
+  }
+
+  bool PostNonNestableDelayedTask(const tracked_objects::Location& from_here,
+                                  const Closure& closure,
+                                  base::TimeDelta delay) override {
+    // Tasks are never nested within the task scheduler.
+    return PostDelayedTask(from_here, closure, delay);
+  }
+
+  bool RunsTasksOnCurrentThread() const override {
+    return GetDelegate()->RunsTasksOnCurrentThread();
+  }
+
+ private:
+  ~SchedulerSingleThreadTaskRunner() override {
+    outer_->UnregisterSchedulerWorker(worker_);
+  }
+
+  void PostTaskNow(std::unique_ptr<Task> task) {
+    scoped_refptr<Sequence> sequence = GetDelegate()->sequence();
+    // If |sequence| is null, then the thread is effectively gone (either
+    // shutdown or joined).
+    if (!sequence)
+      return;
+
+    const bool sequence_was_empty = sequence->PushTask(std::move(task));
+    if (sequence_was_empty) {
+      GetDelegate()->ReEnqueueSequence(std::move(sequence));
+      worker_->WakeUp();
+    }
+  }
+
+  SchedulerWorkerDelegate* GetDelegate() const {
+    return static_cast<SchedulerWorkerDelegate*>(worker_->delegate());
+  }
+
+  SchedulerSingleThreadTaskRunnerManager* const outer_;
+  const TaskTraits traits_;
+  SchedulerWorker* const worker_;
+
+  DISALLOW_COPY_AND_ASSIGN(SchedulerSingleThreadTaskRunner);
+};
+
+SchedulerSingleThreadTaskRunnerManager::SchedulerSingleThreadTaskRunnerManager(
+    const std::vector<SchedulerWorkerPoolParams>& worker_pool_params_vector,
+    const TaskScheduler::WorkerPoolIndexForTraitsCallback&
+        worker_pool_index_for_traits_callback,
+    TaskTracker* task_tracker,
+    DelayedTaskManager* delayed_task_manager)
+    : worker_pool_params_vector_(worker_pool_params_vector),
+      worker_pool_index_for_traits_callback_(
+          worker_pool_index_for_traits_callback),
+      task_tracker_(task_tracker),
+      delayed_task_manager_(delayed_task_manager) {
+  DCHECK_GT(worker_pool_params_vector_.size(), 0U);
+  DCHECK(worker_pool_index_for_traits_callback_);
+  DCHECK(task_tracker_);
+  DCHECK(delayed_task_manager_);
+}
+
+SchedulerSingleThreadTaskRunnerManager::
+    ~SchedulerSingleThreadTaskRunnerManager() {
+#if DCHECK_IS_ON()
+  size_t workers_unregistered_during_join =
+      subtle::NoBarrier_Load(&workers_unregistered_during_join_);
+  DCHECK_EQ(workers_unregistered_during_join, workers_.size())
+      << "There cannot be outstanding SingleThreadTaskRunners upon destruction"
+         "of SchedulerSingleThreadTaskRunnerManager or the Task Scheduler";
+#endif
+}
+
+scoped_refptr<SingleThreadTaskRunner>
+SchedulerSingleThreadTaskRunnerManager::CreateSingleThreadTaskRunnerWithTraits(
+    const TaskTraits& traits) {
+  size_t index = worker_pool_index_for_traits_callback_.Run(traits);
+  DCHECK_LT(index, worker_pool_params_vector_.size());
+  return new SchedulerSingleThreadTaskRunner(
+      this, traits,
+      CreateAndRegisterSchedulerWorker(worker_pool_params_vector_[index]));
+}
+
+void SchedulerSingleThreadTaskRunnerManager::JoinForTesting() {
+  decltype(workers_) local_workers;
+  {
+    AutoSchedulerLock auto_lock(workers_lock_);
+    local_workers = std::move(workers_);
+  }
+
+  for (const auto& worker : local_workers)
+    worker->JoinForTesting();
+
+  {
+    AutoSchedulerLock auto_lock(workers_lock_);
+    DCHECK(workers_.empty())
+        << "New worker(s) unexpectedly registered during join.";
+    workers_ = std::move(local_workers);
+  }
+}
+
+SchedulerWorker*
+SchedulerSingleThreadTaskRunnerManager::CreateAndRegisterSchedulerWorker(
+    const SchedulerWorkerPoolParams& params) {
+  AutoSchedulerLock auto_lock(workers_lock_);
+  int id = next_worker_id_++;
+  auto delegate = MakeUnique<SchedulerWorkerDelegate>(base::StringPrintf(
+      "TaskSchedulerSingleThreadWorker%d%s", id, params.name().c_str()));
+  workers_.emplace_back(SchedulerWorker::Create(
+      params.priority_hint(), std::move(delegate), task_tracker_,
+      SchedulerWorker::InitialState::DETACHED));
+  return workers_.back().get();
+}
+
+void SchedulerSingleThreadTaskRunnerManager::UnregisterSchedulerWorker(
+    SchedulerWorker* worker) {
+  // Cleanup uses a SchedulerLock, so call Cleanup() after releasing
+  // |workers_lock_|.
+  scoped_refptr<SchedulerWorker> worker_to_destroy;
+  {
+    AutoSchedulerLock auto_lock(workers_lock_);
+
+    // We might be joining, so record that a worker was unregistered for
+    // verification at destruction.
+    if (workers_.empty()) {
+#if DCHECK_IS_ON()
+      subtle::NoBarrier_AtomicIncrement(&workers_unregistered_during_join_, 1);
+#endif
+      return;
+    }
+
+    auto worker_iter =
+        std::find_if(workers_.begin(), workers_.end(),
+                     [worker](const scoped_refptr<SchedulerWorker>& candidate) {
+                       return candidate.get() == worker;
+                     });
+    DCHECK(worker_iter != workers_.end());
+    worker_to_destroy = std::move(*worker_iter);
+    workers_.erase(worker_iter);
+  }
+  worker_to_destroy->Cleanup();
+}
+
+}  // namespace internal
+}  // namespace base