Add Lazy Creation and Thread Detachment Support in the Scheduler Worker Pool

base/task_scheduler/scheduler_worker_pool_impl.h

Index: base/task_scheduler/scheduler_worker_pool_impl.h
diff --git a/base/task_scheduler/scheduler_worker_pool_impl.h b/base/task_scheduler/scheduler_worker_pool_impl.h
index 935c79a80c5f000b549628399e0a51dc1180f1ce..59e239298bf171ff42a9ed424a50ecb188935e84 100644
--- a/base/task_scheduler/scheduler_worker_pool_impl.h
+++ b/base/task_scheduler/scheduler_worker_pool_impl.h
@@ -30,6 +30,9 @@
 #include "base/threading/platform_thread.h"
 
 namespace base {
+
+class TimeDelta;
+
 namespace internal {
 
 class DelayedTaskManager;
@@ -55,16 +58,19 @@ class BASE_EXPORT SchedulerWorkerPoolImpl : public SchedulerWorkerPool {
   // Creates a SchedulerWorkerPoolImpl labeled |name| with up to |max_threads|
   // threads of priority |thread_priority|. |io_restriction| indicates whether
   // Tasks on the constructed worker pool are allowed to make I/O calls.
-  // |re_enqueue_sequence_callback| will be invoked after a worker of this
-  // worker pool tries to run a Task. |task_tracker| is used to handle shutdown
-  // behavior of Tasks. |delayed_task_manager| handles Tasks posted with a
-  // delay. Returns nullptr on failure to create a worker pool with at least one
-  // thread.
+  // |suggested_reclaim_time| sets a suggestion on when to reclaim idle threads.
+  // The worker pool is free to ignore this value for performance or correctness
+  // reasons. |re_enqueue_sequence_callback| will be invoked after a worker of
+  // this worker pool tries to run a Task. |task_tracker| is used to handle
+  // shutdown behavior of Tasks. |delayed_task_manager| handles Tasks posted
+  // with a delay. Returns nullptr on failure to create a worker pool with at
+  // least one thread.
   static std::unique_ptr<SchedulerWorkerPoolImpl> Create(
       StringPiece name,
       ThreadPriority thread_priority,
       size_t max_threads,
       IORestriction io_restriction,
+      const TimeDelta& suggested_reclaim_time,
       const ReEnqueueSequenceCallback& re_enqueue_sequence_callback,
       TaskTracker* task_tracker,
       DelayedTaskManager* delayed_task_manager);
@@ -91,6 +97,7 @@ class BASE_EXPORT SchedulerWorkerPoolImpl : public SchedulerWorkerPool {
 
  private:
   class SchedulerWorkerDelegateImpl;
+  class SchedulerSingleThreadTaskRunner;
 
   SchedulerWorkerPoolImpl(StringPiece name,
                           IORestriction io_restriction,
@@ -100,6 +107,7 @@ class BASE_EXPORT SchedulerWorkerPoolImpl : public SchedulerWorkerPool {
   bool Initialize(
       ThreadPriority thread_priority,
       size_t max_threads,
+      const TimeDelta& suggested_reclaim_time,
       const ReEnqueueSequenceCallback& re_enqueue_sequence_callback);
 
   // Wakes up the last worker from this worker pool to go idle, if any.
@@ -108,9 +116,15 @@ class BASE_EXPORT SchedulerWorkerPoolImpl : public SchedulerWorkerPool {
   // Adds |worker| to |idle_workers_stack_|.
   void AddToIdleWorkersStack(SchedulerWorker* worker);
 
+  // Peeks from |idle_workers_stack_|.
+  const SchedulerWorker* PeekAtIdleWorkersStack() const;
+
   // Removes |worker| from |idle_workers_stack_|.
   void RemoveFromIdleWorkersStack(SchedulerWorker* worker);
 
+  // True if JoinForTesting() has been called.
+  bool HasJoinedForTesting();
+
   // The name of this worker pool, used to label its worker threads.
   const std::string name_;
 
@@ -136,7 +150,7 @@ class BASE_EXPORT SchedulerWorkerPoolImpl : public SchedulerWorkerPool {
   // lock as its predecessor so that a worker can be pushed to
   // |idle_workers_stack_| within the scope of a Transaction (more
   // details in GetWork()).
-  SchedulerLock idle_workers_stack_lock_;
+  mutable SchedulerLock idle_workers_stack_lock_;
 
   // Stack of idle workers.
   SchedulerWorkerStack idle_workers_stack_;
@@ -147,6 +161,12 @@ class BASE_EXPORT SchedulerWorkerPoolImpl : public SchedulerWorkerPool {
   // Signaled once JoinForTesting() has returned.
   WaitableEvent join_for_testing_returned_;
 
+  // Synchronizes access to |join_for_testing_called_|.
+  SchedulerLock join_for_testing_called_lock_;
+
+  // Indicates to the delegates that JoinForTesting() has been called.
+  bool join_for_testing_called_;
+
 #if DCHECK_IS_ON()
   // Signaled when all workers have been created.
   WaitableEvent workers_created_;