TaskScheduler [11] Support ExecutionMode::SINGLE_THREADED.

base/task_scheduler/scheduler_worker_thread.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_worker_thread.h"
 
 #include <stddef.h>
 
 #include <utility>
 
+#include "base/lazy_instance.h"
 #include "base/logging.h"
+#include "base/memory/ptr_util.h"
 #include "base/task_scheduler/task_tracker.h"
+#include "base/task_scheduler/utils.h"
+#include "base/threading/thread_local.h"
+#include "base/time/time.h"
 
 namespace base {
 namespace internal {
 
+namespace {
+
+// SchedulerWorkerThread that owns the current thread, if any.
+LazyInstance<ThreadLocalPointer<const SchedulerTaskExecutor>>::Leaky
+    tls_current_worker_thread = LAZY_INSTANCE_INITIALIZER;
+
+// A task runner that runs tasks on a single SchedulerWorkerThread.
+class SchedulerSingleThreadTaskRunner : public SingleThreadTaskRunner {
+ public:
+  SchedulerSingleThreadTaskRunner(const TaskTraits& traits,
+                                  SchedulerTaskExecutor* executor,

[gab, 2016/04/18 18:04:02]

TODO on memory management for this one as well for the sake of keeping track of
them.

[fdoray, 2016/04/18 19:04:50]

Done.

+                                  TaskTracker* task_tracker,
+                                  DelayedTaskManager* delayed_task_manager)
+      : traits_(traits),
+        executor_(executor),
+        task_tracker_(task_tracker),
+        delayed_task_manager_(delayed_task_manager) {}
+
+  // SingleThreadTaskRunner:
+  bool PostDelayedTask(const tracked_objects::Location& from_here,
+                       const Closure& closure,
+                       TimeDelta delay) override {
+    // Post the task as part of |sequence|.
+    return PostTaskToExecutor(from_here, closure, traits_, delay, sequence_,
+                              executor_, task_tracker_, delayed_task_manager_);
+  }
+
+  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 tls_current_worker_thread.Get().Get() == executor_;
+  }
+
+ private:
+  ~SchedulerSingleThreadTaskRunner() override = default;
+
+  // Sequence for all Tasks posted through this TaskRunner.
+  const scoped_refptr<Sequence> sequence_ = new Sequence;
+
+  const TaskTraits traits_;
+  SchedulerTaskExecutor* const executor_;
+  TaskTracker* const task_tracker_;
+  DelayedTaskManager* const delayed_task_manager_;
+
+  DISALLOW_COPY_AND_ASSIGN(SchedulerSingleThreadTaskRunner);
+};
+
+}  // namespace
+
 std::unique_ptr<SchedulerWorkerThread>
 SchedulerWorkerThread::CreateSchedulerWorkerThread(
     ThreadPriority thread_priority,
     Delegate* delegate,
-    TaskTracker* task_tracker) {
+    TaskTracker* task_tracker,
+    DelayedTaskManager* delayed_task_manager,
+    const PriorityQueue* predecessor_priority_queue) {
   std::unique_ptr<SchedulerWorkerThread> worker_thread(
-      new SchedulerWorkerThread(thread_priority, delegate, task_tracker));
+      new SchedulerWorkerThread(thread_priority, delegate, task_tracker,
+                                delayed_task_manager,
+                                predecessor_priority_queue));
 
   if (worker_thread->thread_handle_.is_null())
     return nullptr;
   return worker_thread;
 }
 
 SchedulerWorkerThread::~SchedulerWorkerThread() {
   DCHECK(ShouldExitForTesting());
 }
 
+scoped_refptr<SingleThreadTaskRunner>
+SchedulerWorkerThread::CreateTaskRunnerWithTraits(const TaskTraits& traits) {
+  return make_scoped_refptr(new SchedulerSingleThreadTaskRunner(
+      traits, this, task_tracker_, delayed_task_manager_));
+}
+
 void SchedulerWorkerThread::WakeUp() {
   wake_up_event_.Signal();
 }
 
 void SchedulerWorkerThread::JoinForTesting() {
   {
     AutoSchedulerLock auto_lock(should_exit_for_testing_lock_);
     should_exit_for_testing_ = true;
   }
   WakeUp();
   PlatformThread::Join(thread_handle_);
 }
 
-SchedulerWorkerThread::SchedulerWorkerThread(ThreadPriority thread_priority,
-                                             Delegate* delegate,
-                                             TaskTracker* task_tracker)
+void SchedulerWorkerThread::PostTaskWithSequence(
+    std::unique_ptr<Task> task,
+    scoped_refptr<Sequence> sequence) {
+  DCHECK(task);
+  DCHECK(sequence);
+
+  const bool sequence_was_empty = AddTaskToSequenceAndPriorityQueue(
+      std::move(task), std::move(sequence), &single_threaded_priority_queue_);
+
+  // If |sequence| wasn't empty before |task| was inserted into it, the worker
+  // thread has already been woken up to run it.

[gab, 2016/04/18 18:04:02]

How about s/run/process/ (at first I thought "it" referred to the task instead
of the sequence and I think "process" makes this clearer, i.e. process the
sequence by running its tasks)

[fdoray, 2016/04/18 19:04:50]

Done.

+  if (sequence_was_empty)
+    WakeUp();

[gab, 2016/04/18 18:04:02]

Add a TODO to check for removal from idle stack (as you seem to be doing that in
a follow-up CL)

[fdoray, 2016/04/18 19:04:50]

Done.

+}
+
+SchedulerWorkerThread::SchedulerWorkerThread(
+    ThreadPriority thread_priority,
+    Delegate* delegate,
+    TaskTracker* task_tracker,
+    DelayedTaskManager* delayed_task_manager,
+    const PriorityQueue* predecessor_priority_queue)
     : wake_up_event_(false, false),
+      single_threaded_priority_queue_(predecessor_priority_queue),
       delegate_(delegate),
-      task_tracker_(task_tracker) {
+      task_tracker_(task_tracker),
+      delayed_task_manager_(delayed_task_manager) {
   DCHECK(delegate_);
   DCHECK(task_tracker_);
+  DCHECK(delayed_task_manager_);
+  DCHECK(predecessor_priority_queue);
 
   const size_t kDefaultStackSize = 0;
   PlatformThread::CreateWithPriority(kDefaultStackSize, this, &thread_handle_,
                                      thread_priority);
 }
 
 void SchedulerWorkerThread::ThreadMain() {
   delegate_->OnMainEntry();
+  tls_current_worker_thread.Get().Set(this);
 
   // A SchedulerWorkerThread starts out sleeping.
   wake_up_event_.Wait();
 
   while (!task_tracker_->shutdown_completed() && !ShouldExitForTesting()) {
     // Get the sequence containing the next task to execute.
-    scoped_refptr<Sequence> sequence = delegate_->GetWork(this);
+    bool is_single_threaded_sequence = false;
+    scoped_refptr<Sequence> sequence = delegate_->GetWork(
+        this, &single_threaded_priority_queue_, &is_single_threaded_sequence);
 
     if (!sequence) {
       wake_up_event_.Wait();
       continue;
     }
 
     task_tracker_->RunTask(sequence->PeekTask());
 
     const bool sequence_became_empty = sequence->PopTask();
 
     // If |sequence| isn't empty immediately after the pop, enqueue it to
     // maintain the invariant that a non-empty Sequence is always referenced by
     // either a PriorityQueue or a SchedulerWorkerThread. If it is empty and
     // there are live references to it, it will be enqueued when a Task is added
     // to it. Otherwise, it will be destroyed at the end of this scope.
-    if (!sequence_became_empty)
-      delegate_->EnqueueSequence(std::move(sequence));
+    if (!sequence_became_empty) {
+      if (is_single_threaded_sequence) {
+        const auto sort_key = sequence->GetSortKey();
+        single_threaded_priority_queue_.BeginTransaction()->Push(
+            WrapUnique(new PriorityQueue::SequenceAndSortKey(
+                std::move(sequence), sort_key)));
+      } else {
+        delegate_->EnqueueSequence(std::move(sequence));
+      }
+    }
 
     // Calling WakeUp() guarantees that this SchedulerWorkerThread will run
     // Tasks from Sequences returned by the GetWork() method of |delegate_|
     // until it returns nullptr. Resetting |wake_up_event_| here doesn't break
     // this invariant and avoids a useless loop iteration before going to sleep
     // if WakeUp() is called while this SchedulerWorkerThread is awake.
     wake_up_event_.Reset();
   }
 }
 
 bool SchedulerWorkerThread::ShouldExitForTesting() const {
   AutoSchedulerLock auto_lock(should_exit_for_testing_lock_);
   return should_exit_for_testing_;
 }
 
 }  // namespace internal
 }  // namespace base