TaskScheduler: Delegate instead of callbacks for SchedulerWorkerThread.

base/task_scheduler/scheduler_worker_thread.cc

Index: base/task_scheduler/scheduler_worker_thread.cc
diff --git a/base/task_scheduler/scheduler_worker_thread.cc b/base/task_scheduler/scheduler_worker_thread.cc
index e03726a0c09b886167d863057cb56a25def51d63..3ae95bf065deb25856eb946808bb30e6624a5d8e 100644
--- a/base/task_scheduler/scheduler_worker_thread.cc
+++ b/base/task_scheduler/scheduler_worker_thread.cc
@@ -9,6 +9,7 @@
 #include <utility>
 
 #include "base/logging.h"
+#include "base/task_scheduler/scheduler_worker_thread_delegate.h"
 #include "base/task_scheduler/task_tracker.h"
 
 namespace base {
@@ -17,14 +18,10 @@ namespace internal {
 std::unique_ptr<SchedulerWorkerThread>
 SchedulerWorkerThread::CreateSchedulerWorkerThread(
     ThreadPriority thread_priority,
-    const Closure& main_entry_callback,
-    const GetWorkCallback& get_work_callback,
-    const RanTaskFromSequenceCallback& ran_task_from_sequence_callback,
+    SchedulerWorkerThreadDelegate* delegate,
     TaskTracker* task_tracker) {
   std::unique_ptr<SchedulerWorkerThread> worker_thread(
-      new SchedulerWorkerThread(thread_priority, main_entry_callback,
-                                get_work_callback,
-                                ran_task_from_sequence_callback, task_tracker));
+      new SchedulerWorkerThread(thread_priority, delegate, task_tracker));
 
   if (worker_thread->thread_handle_.is_null())
     return nullptr;
@@ -50,18 +47,12 @@ void SchedulerWorkerThread::JoinForTesting() {
 
 SchedulerWorkerThread::SchedulerWorkerThread(
     ThreadPriority thread_priority,
-    const Closure& main_entry_callback,
-    const GetWorkCallback& get_work_callback,
-    const RanTaskFromSequenceCallback& ran_task_from_sequence_callback,
+    SchedulerWorkerThreadDelegate* delegate,
     TaskTracker* task_tracker)
     : wake_up_event_(false, false),
-      main_entry_callback_(main_entry_callback),
-      get_work_callback_(get_work_callback),
-      ran_task_from_sequence_callback_(ran_task_from_sequence_callback),
+      delegate_(delegate),
       task_tracker_(task_tracker) {
-  DCHECK(!main_entry_callback_.is_null());
-  DCHECK(!get_work_callback_.is_null());
-  DCHECK(!ran_task_from_sequence_callback_.is_null());
+  DCHECK(delegate_);
   DCHECK(task_tracker_);
 
   static const size_t kDefaultStackSize = 0;
@@ -70,14 +61,14 @@ SchedulerWorkerThread::SchedulerWorkerThread(
 }
 
 void SchedulerWorkerThread::ThreadMain() {
-  main_entry_callback_.Run();
+  delegate_->OnMainEntry();
 
   // 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 = get_work_callback_.Run(this);
+    scoped_refptr<Sequence> sequence = delegate_->GetWork();

[robliao, 2016/04/06 20:50:18]

What's the plan for getting work from the single threaded priority queue?

[fdoray, 2016/04/06 21:11:38]

3 possible solutions:
1) Single-threaded PQ is owned by worker thread. Worker thread passes a pointer
to its single-threaded PQ to GetWork().
2) Single-threaded PQ is owned by worker thread. Worker thread passes |this| to
GetWork. Delegate accesses the single-threaded PQ via an accessor.
3) Thread pool has a map WorkerThread* -> single-threaded PQ. Worker thread
passes |this| to GetWork. Delegate (thread pool) finds the single-threaded PQ in
its map.

(1) is great because the single-threaded PQ lives with its WorkerThread (no need
to make sure that they are created/destroyed at the same time). I don't like
(2). (3) is great because worker thread doesn't have to know about PQs.

I planned to land this CL as-is and add the arguments we need to GetWork() in
the CL that implements the SINGLE_THREADED ExecutionMode.

[robliao, 2016/04/06 21:28:20]

Sounds good. Just wanted to me sure this wasn't omitted since we did pass the
this pointer through on the original CL.

 
     if (!sequence) {
       wake_up_event_.Wait();
@@ -85,15 +76,17 @@ void SchedulerWorkerThread::ThreadMain() {
     }
 
     task_tracker_->RunTask(sequence->PeekTask());
-    ran_task_from_sequence_callback_.Run(this, std::move(sequence));
+    delegate_->RanTaskFromSequence(std::move(sequence));
 
     // Calling WakeUp() guarantees that this SchedulerWorkerThread will run
-    // Tasks from Sequences returned by |get_work_callback_| until the callback
-    // 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.
+    // 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();
   }
+
+  delegate_->OnMainExit();
 }
 
 bool SchedulerWorkerThread::ShouldExitForTesting() const {