TaskScheduler [7] SchedulerThreadPool

base/task_scheduler/scheduler_thread_pool.cc

+// 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.
+
+#include "base/task_scheduler/scheduler_thread_pool.h"
+
+#include <utility>
+
+#include "base/bind.h"
+#include "base/bind_helpers.h"
+#include "base/lazy_instance.h"
+#include "base/logging.h"
+#include "base/memory/ptr_util.h"
+#include "base/task_scheduler/utils.h"
+#include "base/threading/thread_local.h"
+
+namespace base {
+namespace internal {
+
+namespace {
+
+// SchedulerThreadPool that owns the current thread, if any.
+LazyInstance<ThreadLocalPointer<const SchedulerTaskExecutor>>::Leaky
+    tls_current_thread_pool = LAZY_INSTANCE_INITIALIZER;
+
+// A task runner that runs tasks with the PARALLEL ExecutionMode.
+class SchedulerParallelTaskRunner : public TaskRunner {
+ public:
+  SchedulerParallelTaskRunner(const TaskTraits& traits,
+                              TaskTracker* task_tracker,
+                              SchedulerTaskExecutor* executor)
+      : traits_(traits), task_tracker_(task_tracker), executor_(executor) {}
+
+  // TaskRunner:
+  bool PostDelayedTask(const tracked_objects::Location& from_here,
+                       const Closure& closure,
+                       TimeDelta delay) override {
+    // Post the task as part of a one-off single-task Sequence.
+    return PostTaskHelper(from_here, closure, traits_, delay,
+                          make_scoped_refptr(new Sequence), executor_,
+                          task_tracker_);
+  }
+
+  bool RunsTasksOnCurrentThread() const override {
+    return tls_current_thread_pool.Get().Get() == executor_;
+  }
+
+ private:
+  ~SchedulerParallelTaskRunner() override = default;
+
+  const TaskTraits traits_;
+  TaskTracker* const task_tracker_;
+
+  // TODO(robliao): Use a WeakPtr instead of a raw pointer. A
+  // SchedulerTaskExecutor is never deleted in production, but it's better not
+  // to spread this assumption throughout the scheduler.

[gab, 2016/04/14 19:34:16]

A WeakPtr isn't ever possible here as PostTask is clearly called from multiple
threads and therefore it's impossible to have all lookups be on the same thread
(as it potentially was for the instance in DelayedTaskManager).

Maybe something like this on the constructor instead:

// Constructs a SchedulerParallelTaskRunner which can be used to post tasks so
long as |executor| is alive.
// TODO(robliao): Find a concrete way to manage |executor|'s memory. 
SchedulerParallelTaskRunner(...

[fdoray, 2016/04/14 23:46:58]

Done.

+  SchedulerTaskExecutor* const executor_;
+
+  DISALLOW_COPY_AND_ASSIGN(SchedulerParallelTaskRunner);
+};
+
+}  // namespace
+
+class SchedulerThreadPool::SchedulerWorkerThreadDelegateImpl
+    : public SchedulerWorkerThread::Delegate {
+ public:
+  SchedulerWorkerThreadDelegateImpl(
+      SchedulerThreadPool* outer,
+      const EnqueueSequenceCallback enqueue_sequence_callback);
+  ~SchedulerWorkerThreadDelegateImpl() override;
+
+  // SchedulerWorkerThread::Delegate:
+  void OnMainEntry() override;
+  scoped_refptr<Sequence> GetWork(
+      SchedulerWorkerThread* worker_thread) override;
+  void EnqueueSequence(scoped_refptr<Sequence> sequence) override;
+
+ private:
+  SchedulerThreadPool* outer_;
+  const EnqueueSequenceCallback enqueue_sequence_callback_;
+
+  DISALLOW_COPY_AND_ASSIGN(SchedulerWorkerThreadDelegateImpl);
+};
+
+SchedulerThreadPool::~SchedulerThreadPool() {
+  // SchedulerThreadPool should never be deleted in production unless its
+  // initialization failed.
+  DCHECK(join_for_testing_returned_.IsSignaled() || worker_threads_.empty());
+}
+
+std::unique_ptr<SchedulerThreadPool> SchedulerThreadPool::CreateThreadPool(
+    ThreadPriority thread_priority,
+    size_t max_threads,
+    const EnqueueSequenceCallback& enqueue_sequence_callback,
+    TaskTracker* task_tracker) {
+  std::unique_ptr<SchedulerThreadPool> thread_pool(
+      new SchedulerThreadPool(enqueue_sequence_callback, task_tracker));
+  if (thread_pool->Initialize(thread_priority, max_threads))
+    return thread_pool;
+  return nullptr;
+}
+
+scoped_refptr<TaskRunner> SchedulerThreadPool::CreateTaskRunnerWithTraits(
+    const TaskTraits& traits,
+    ExecutionMode execution_mode) {
+  switch (execution_mode) {
+    case ExecutionMode::PARALLEL:
+      return make_scoped_refptr(
+          new SchedulerParallelTaskRunner(traits, task_tracker_, this));
+
+    case ExecutionMode::SEQUENCED:
+    case ExecutionMode::SINGLE_THREADED:
+      // TODO(fdoray): Support SEQUENCED and SINGLE_THREADED TaskRunners.
+      NOTREACHED();
+      return nullptr;
+  }
+
+  NOTREACHED();
+  return nullptr;
+}
+
+void SchedulerThreadPool::EnqueueSequence(
+    scoped_refptr<Sequence> sequence,
+    const SequenceSortKey& sequence_sort_key) {
+  shared_priority_queue_.BeginTransaction()->Push(
+      WrapUnique(new PriorityQueue::SequenceAndSortKey(std::move(sequence),
+                                                       sequence_sort_key)));
+
+  // The thread calling this method just ran a Task from |sequence| and will
+  // soon try to get another Sequence from which to run a Task. If the thread
+  // belongs to this pool, it will get that Sequence from
+  // |shared_priority_queue_|. When that's the case, there is no need to wake up
+  // another thread after |sequence| is inserted in |shared_priority_queue_|. If
+  // we did wake up another thread, we would waste resources by having more
+  // threads trying to get a Sequence from |shared_priority_queue_| than the
+  // number of Sequences in it.
+  if (tls_current_thread_pool.Get().Get() != this)
+    WakeUpOneThread();
+}
+
+void SchedulerThreadPool::WaitForAllWorkerThreadsIdleForTesting() {
+  AutoSchedulerLock auto_lock(idle_worker_threads_stack_lock_);
+  while (idle_worker_threads_stack_.size() < worker_threads_.size())
+    idle_worker_threads_stack_cv_for_testing_->Wait();
+}
+
+void SchedulerThreadPool::JoinForTesting() {
+  for (const auto& worker_thread : worker_threads_)
+    worker_thread->JoinForTesting();
+
+  DCHECK(!join_for_testing_returned_.IsSignaled());
+  join_for_testing_returned_.Signal();
+}
+
+void SchedulerThreadPool::PostTaskWithSequence(
+    std::unique_ptr<Task> task,
+    scoped_refptr<Sequence> sequence) {
+  DCHECK(task);
+  DCHECK(sequence);
+
+  // Verify that we are passed |task|'s delayed run time (i.e. |task| is ready

[gab, 2016/04/14 19:34:16]

s/passed/past/

rm "we", e.g.:

// Confirm that |task| is ready to run (its delayed run time is either null or
in the past).

[fdoray, 2016/04/14 23:46:58]

Done (removed the DCHECK here, kept in in utils.cc).

+  // to run).
+  DCHECK_LE(task->delayed_run_time, TimeTicks::Now());
+
+  const bool sequence_was_empty = PostTaskWithSequenceHelper(
+      std::move(task), std::move(sequence), &shared_priority_queue_);
+
+  // No thread has already been woken up to run Tasks from |sequence| if it was
+  // empty before |task| was inserted into it.
+  if (sequence_was_empty)
+    WakeUpOneThread();
+}
+
+SchedulerThreadPool::SchedulerWorkerThreadDelegateImpl::
+    SchedulerWorkerThreadDelegateImpl(
+        SchedulerThreadPool* outer,
+        const EnqueueSequenceCallback enqueue_sequence_callback)
+    : outer_(outer), enqueue_sequence_callback_(enqueue_sequence_callback) {}
+
+SchedulerThreadPool::SchedulerWorkerThreadDelegateImpl::
+    ~SchedulerWorkerThreadDelegateImpl() = default;
+
+void SchedulerThreadPool::SchedulerWorkerThreadDelegateImpl::OnMainEntry() {
+  DCHECK(!tls_current_thread_pool.Get().Get());
+  tls_current_thread_pool.Get().Set(outer_);
+}
+
+scoped_refptr<Sequence>
+SchedulerThreadPool::SchedulerWorkerThreadDelegateImpl::GetWork(
+    SchedulerWorkerThread* worker_thread) {
+  std::unique_ptr<PriorityQueue::Transaction> transaction(
+      outer_->shared_priority_queue_.BeginTransaction());
+  const auto sequence_and_sort_key = transaction->Peek();
+
+  if (sequence_and_sort_key.is_null()) {
+    // |transaction| is kept alive while |worker_thread| is added to
+    // |idle_worker_threads_stack_| to avoid this race:
+    // 1. This thread creates a Transaction, finds |shared_priority_queue_|
+    //    empty and ends the Transaction.
+    // 2. Other thread creates a Transaction, inserts a Sequence into
+    //    |shared_priority_queue_| and ends the Transaction. This can't happen
+    //    if the Transaction of step 1 is still active because because there can
+    //    only be one active Transaction per PriorityQueue at a time.
+    // 3. Other thread calls WakeUpOneThread(). No thread is woken up because
+    //    |idle_worker_threads_stack_| is empty.
+    // 4. This thread adds itself to |idle_worker_threads_stack_| and goes to
+    //    sleep. No thread runs the Sequence inserted in step 2.
+    outer_->AddToIdleWorkerThreadsStack(worker_thread);
+    return nullptr;
+  }
+
+  transaction->Pop();
+  return sequence_and_sort_key.sequence;
+}
+
+void SchedulerThreadPool::SchedulerWorkerThreadDelegateImpl::EnqueueSequence(
+    scoped_refptr<Sequence> sequence) {
+  enqueue_sequence_callback_.Run(std::move(sequence));
+}
+
+SchedulerThreadPool::SchedulerThreadPool(
+    const EnqueueSequenceCallback& enqueue_sequence_callback,
+    TaskTracker* task_tracker)
+    : idle_worker_threads_stack_lock_(shared_priority_queue_.container_lock()),
+      idle_worker_threads_stack_cv_for_testing_(
+          idle_worker_threads_stack_lock_.CreateConditionVariable()),
+      join_for_testing_returned_(true, false),
+      worker_thread_delegate_(
+          new SchedulerWorkerThreadDelegateImpl(this,
+                                                enqueue_sequence_callback)),
+      task_tracker_(task_tracker) {
+  DCHECK(task_tracker_);
+}
+
+bool SchedulerThreadPool::Initialize(ThreadPriority thread_priority,
+                                     size_t max_threads) {
+  AutoSchedulerLock auto_lock(idle_worker_threads_stack_lock_);
+
+  DCHECK(worker_threads_.empty());
+
+  for (size_t i = 0; i < max_threads; ++i) {
+    std::unique_ptr<SchedulerWorkerThread> worker_thread =
+        SchedulerWorkerThread::CreateSchedulerWorkerThread(
+            thread_priority, worker_thread_delegate_.get(), task_tracker_);
+    if (!worker_thread)
+      break;
+    idle_worker_threads_stack_.push(worker_thread.get());
+    worker_threads_.push_back(std::move(worker_thread));
+  }
+
+  return !worker_threads_.empty();
+}
+
+void SchedulerThreadPool::WakeUpOneThread() {
+  SchedulerWorkerThread* worker_thread = PopOneIdleWorkerThread();
+  if (worker_thread)
+    worker_thread->WakeUp();
+}
+
+void SchedulerThreadPool::AddToIdleWorkerThreadsStack(
+    SchedulerWorkerThread* worker_thread) {
+  AutoSchedulerLock auto_lock(idle_worker_threads_stack_lock_);
+  idle_worker_threads_stack_.push(worker_thread);
+  DCHECK_LE(idle_worker_threads_stack_.size(), worker_threads_.size());
+
+  if (idle_worker_threads_stack_.size() == worker_threads_.size())
+    idle_worker_threads_stack_cv_for_testing_->Broadcast();
+}
+
+SchedulerWorkerThread* SchedulerThreadPool::PopOneIdleWorkerThread() {
+  AutoSchedulerLock auto_lock(idle_worker_threads_stack_lock_);
+
+  if (idle_worker_threads_stack_.empty())
+    return nullptr;
+
+  auto worker_thread = idle_worker_threads_stack_.top();
+  idle_worker_threads_stack_.pop();
+  return worker_thread;
+}
+
+}  // namespace internal
+}  // namespace base