DomStorage commit task sequencing.

webkit/dom_storage/dom_storage_task_runner.h

 // Copyright (c) 2012 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.
 
 #ifndef WEBKIT_DOM_STORAGE_DOM_STORAGE_TASK_RUNNER_
 #define WEBKIT_DOM_STORAGE_DOM_STORAGE_TASK_RUNNER_
 #pragma once
 
 #include "base/memory/ref_counted.h"
 #include "base/sequenced_task_runner.h"
 #include "base/threading/sequenced_worker_pool.h"
 #include "base/time.h"
 
 namespace base {
 class MessageLoopProxy;
 }
 
 namespace dom_storage {
 
-// Tasks must run serially with respect to one another, but may
-// execute on different OS threads. The base class is implemented
-// in terms of a MessageLoopProxy.
-class DomStorageTaskRunner : public base::SequencedTaskRunner {
+// Interface for posting dom storage related tasks. There
+// are two logical task sequences, the primary sequence is
+// the read where most tasks are performed, the commit sequence
+// is used internally for committing data to disk. The base TaskRunner
+// interfaces maps to the primary sequence and allow callers to post
+// non shutdown blocking tasks on it. An additional method allows callers
+// to post shutdown blocking tasks to either sequence.
+class DomStorageTaskRunner : public base::TaskRunner {
  public:
-  explicit DomStorageTaskRunner(base::MessageLoopProxy* message_loop);
+  enum SequenceID {
+    PRIMARY_SEQUENCE,
+    COMMIT_SEQUENCE
+  };
+
   virtual ~DomStorageTaskRunner();
 
-  // The PostTask() method, defined by TaskRunner, schedules a task
-  // to run immediately.
+  // The PostTask() method, defined by TaskRunner, schedules
+  // a non shutdown blocking READ_SEQUENCE task to run immediately.

[benm (inactive), 2012/03/20 13:39:16]

s/READ_/PRIMARY_/ and below

 
-  // Schedules a task to be run after a delay.
+  // Schedules a non shutdown blocking READ_SEQUENCE task to be run
+  // after a delay.
   virtual bool PostDelayedTask(
       const tracked_objects::Location& from_here,
       const base::Closure& task,
       base::TimeDelta delay) OVERRIDE;
 
   // DEPRECATED: Only here because base::TaskRunner requires it, implemented
   // by calling the virtual PostDelayedTask(..., TimeDelta) variant.
   virtual bool PostDelayedTask(
       const tracked_objects::Location& from_here,
       const base::Closure& task,
       int64 delay_ms) OVERRIDE;
 
   // Only here because base::TaskRunner requires it, the return
   // value is hard coded to true.
   virtual bool RunsTasksOnCurrentThread() const OVERRIDE;
 
-  // SequencedTaskRunner overrides, these are implemented in
-  // terms of PostDelayedTask and the latter is similarly deprecated.
-  virtual bool PostNonNestableDelayedTask(
+  virtual bool PostShutdownBlockingTask(
       const tracked_objects::Location& from_here,
-      const base::Closure& task,
-      base::TimeDelta delay) OVERRIDE;
-  virtual bool PostNonNestableDelayedTask(
-      const tracked_objects::Location& from_here,
-      const base::Closure& task,
-      int64 delay_ms) OVERRIDE;
+      SequenceID sequence_id,
+      const base::Closure& task) = 0;
 
  protected:
+  explicit DomStorageTaskRunner(base::MessageLoopProxy* message_loop);
+
   const scoped_refptr<base::MessageLoopProxy> message_loop_;
 };
 
 // A derived class that utlizes the SequenceWorkerPool under a

[benm (inactive), 2012/03/20 13:39:16]

remove "a"

-// dom_storage specific SequenceToken. The MessageLoopProxy
+// dom_storage specific SequenceTokens. The MessageLoopProxy
 // is used to delay scheduling on the worker pool.
 class DomStorageWorkerPoolTaskRunner : public DomStorageTaskRunner {
  public:
   DomStorageWorkerPoolTaskRunner(
       base::SequencedWorkerPool* sequenced_worker_pool,
-      base::SequencedWorkerPool::SequenceToken sequence_token,
+      base::SequencedWorkerPool::SequenceToken primary_sequence_token,
+      base::SequencedWorkerPool::SequenceToken commit_sequence_token,
       base::MessageLoopProxy* delayed_task_loop);
   virtual ~DomStorageWorkerPoolTaskRunner();
 
-  // Schedules a sequenced worker task to be run after a delay.
   virtual bool PostDelayedTask(
       const tracked_objects::Location& from_here,
       const base::Closure& task,
       base::TimeDelta delay) OVERRIDE;
 
-  base::SequencedWorkerPool::SequenceToken sequence_token() const;
+  virtual bool PostShutdownBlockingTask(
+      const tracked_objects::Location& from_here,
+      SequenceID sequence_id,
+      const base::Closure& task) OVERRIDE;
 
  private:
   const scoped_refptr<base::SequencedWorkerPool> sequenced_worker_pool_;
-  base::SequencedWorkerPool::SequenceToken sequence_token_;
+  base::SequencedWorkerPool::SequenceToken primary_sequence_token_;
+  base::SequencedWorkerPool::SequenceToken commit_sequence_token_;
 };
 
 // A derived class used in unit tests that causes us to ignore the
 // delay in PostDelayedTask so we don't need to block in unit tests
 // for the timeout to expire.
 class MockDomStorageTaskRunner : public DomStorageTaskRunner {
  public:
   explicit MockDomStorageTaskRunner(base::MessageLoopProxy* message_loop);
   virtual ~MockDomStorageTaskRunner() {}
 
   virtual bool PostDelayedTask(
       const tracked_objects::Location& from_here,
       const base::Closure& task,
       base::TimeDelta delay) OVERRIDE;
+
+  virtual bool PostShutdownBlockingTask(
+      const tracked_objects::Location& from_here,
+      SequenceID sequence_id,
+      const base::Closure& task) OVERRIDE;
 };
 
 }  // namespace dom_storage
 
 #endif  // WEBKIT_DOM_STORAGE_DOM_STORAGE_TASK_RUNNER_