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 {
+
+// Shared PriorityQueue of a thread's SchedulerThreadPool. Not set for threads
+// that don't belong to a SchedulerThreadPool.
+LazyInstance<ThreadLocalPointer<const PriorityQueue>>::Leaky
+    tls_current_shared_priority_queue = LAZY_INSTANCE_INITIALIZER;
+
+// A task runner that runs tasks with the PARALLEL ExecutionMode.
+class SchedulerParallelTaskRunner : public TaskRunner {
+ public:
+  SchedulerParallelTaskRunner(const TaskTraits& traits,
+                              PriorityQueue* priority_queue,
+                              TaskTracker* task_tracker)
+      : traits_(traits),
+        priority_queue_(priority_queue),
+        task_tracker_(task_tracker) {}
+
+  // TaskRunner:
+  bool PostDelayedTask(const tracked_objects::Location& from_here,
+                       const Closure& closure,
+                       TimeDelta delay) override {
+    // TODO(fdoray): Support delayed tasks.
+    DCHECK(delay.is_zero());
+
+    // Post the task as part of a one-off single-task Sequence.
+    return PostTaskHelper(WrapUnique(new Task(from_here, closure, traits_)),
+                          make_scoped_refptr(new Sequence), priority_queue_,
+                          task_tracker_);
+  }
+
+  bool RunsTasksOnCurrentThread() const override {
+    return tls_current_shared_priority_queue.Get().Get() == priority_queue_;
+  }
+
+ private:
+  ~SchedulerParallelTaskRunner() override = default;
+
+  const TaskTraits traits_;
+  PriorityQueue* const priority_queue_;
+  TaskTracker* const task_tracker_;
+
+  DISALLOW_COPY_AND_ASSIGN(SchedulerParallelTaskRunner);
+};
+
+}  // namespace
+
+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;
+}
+
+SchedulerThreadPool::~SchedulerThreadPool() {
+#if DCHECK_IS_ON()
+  // SchedulerThreadPool should never be deleted in production unless its
+  // initialization failed.
+  AutoSchedulerLock auto_lock(worker_threads_lock_);
+  DCHECK(join_for_testing_returned_.IsSignaled() || worker_threads_.empty());
+#endif  // DCHECK_IS_ON()
+}
+
+scoped_refptr<TaskRunner> SchedulerThreadPool::CreateTaskRunnerWithTraits(
+    const TaskTraits& traits,
+    ExecutionMode execution_mode) {
+  switch (execution_mode) {
+    case ExecutionMode::PARALLEL:
+      return make_scoped_refptr(new SchedulerParallelTaskRunner(
+          traits, &shared_priority_queue_, task_tracker_));
+
+    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) {
+  auto sequence_and_sort_key = WrapUnique(new PriorityQueue::SequenceAndSortKey(
+      std::move(sequence), sequence_sort_key));
+  auto transaction = shared_priority_queue_.BeginTransaction();
+
+  // 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_shared_priority_queue.Get().Get() == &shared_priority_queue_)
+    transaction->PushNoWakeUp(std::move(sequence_and_sort_key));
+  else
+    transaction->Push(std::move(sequence_and_sort_key));
+}
+
+void SchedulerThreadPool::WaitForAllWorkerThreadsIdleForTesting() {
+  AutoSchedulerLock auto_lock(worker_threads_lock_);
+  while (idle_worker_threads_stack_.size() < worker_threads_.size())
+    idle_worker_threads_stack_cv_for_testing_->Wait();
+}
+
+void SchedulerThreadPool::JoinForTesting() {
+  std::vector<SchedulerWorkerThread*> worker_threads_copy;
+  {
+    AutoSchedulerLock auto_lock(worker_threads_lock_);
+    for (const auto& worker_thread : worker_threads_)
+      worker_threads_copy.push_back(worker_thread.get());
+  }
+
+  // Join threads without holding |worker_threads_lock_|. Otherwise, a deadlock
+  // could occur when they call GetWork().
+  for (const auto& worker_thread : worker_threads_copy)
+    worker_thread->JoinForTesting();
+

[gab, 2016/04/08 17:56:00]

Do we need to verify that worker_threads_copy is still equal to |worker_threads|
after joining? Otherwise we risk missing a thread created in between?

[fdoray, 2016/04/08 19:00:05]

I would like to put back the comment that says that |worker_threads_| is only
modified during initialization and remove the copy here. 

I would like to implement ramp up / down without changing |worker_threads_|.
SchedulerWorkerThreads would be created with their SchedulerThreadPool and would
never be deleted. The thread that they manage internally could however exit and
be re-created on WakeUp().

[gab, 2016/04/08 21:10:50]

Okay, feel free to put it back for now and we'll see when we get to that CL.

+  DCHECK(!join_for_testing_returned_.IsSignaled());
+  join_for_testing_returned_.Signal();
+}
+
+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_shared_priority_queue.Get().Get());
+  tls_current_shared_priority_queue.Get().Set(&outer_->shared_priority_queue_);
+}
+
+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)
+    : shared_priority_queue_(
+          Bind(&SchedulerThreadPool::WakeUpOneThread, Unretained(this))),
+      worker_threads_lock_(shared_priority_queue_.container_lock()),
+      idle_worker_threads_stack_cv_for_testing_(
+          worker_threads_lock_.CreateConditionVariable()),
+      join_for_testing_returned_(true, false),
+      worker_thread_delegate_(this, enqueue_sequence_callback),
+      task_tracker_(task_tracker) {
+  DCHECK(task_tracker_);
+}
+
+bool SchedulerThreadPool::Initialize(ThreadPriority thread_priority,
+                                     size_t max_threads) {
+  AutoSchedulerLock auto_lock(worker_threads_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_, 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;
+  {
+    AutoSchedulerLock auto_lock(worker_threads_lock_);
+
+    if (idle_worker_threads_stack_.empty())
+      return;
+
+    worker_thread = idle_worker_threads_stack_.top();
+    idle_worker_threads_stack_.pop();
+  }
+  worker_thread->WakeUp();
+}
+
+void SchedulerThreadPool::AddToIdleWorkerThreadsStack(
+    SchedulerWorkerThread* worker_thread) {
+  AutoSchedulerLock auto_lock(worker_threads_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();
+}
+
+}  // namespace internal
+}  // namespace base