Fix up SequencedWorkerPool in preparation for making it a TaskRunner

base/threading/sequenced_worker_pool.h

-// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// 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 BASE_THREADING_SEQUENCED_WORKER_POOL_H_
 #define BASE_THREADING_SEQUENCED_WORKER_POOL_H_
 #pragma once
 
+#include <cstddef>
 #include <string>
 
-#include "base/callback.h"
-#include "base/memory/linked_ptr.h"
+#include "base/base_export.h"
+#include "base/basictypes.h"
+#include "base/callback_forward.h"
 #include "base/memory/ref_counted.h"
-#include "base/tracked_objects.h"
-#include "base/base_export.h"
+#include "base/memory/scoped_ptr.h"
+
+namespace tracked_objects {
+class Location;
+}  // namespace tracked_objects
 
 namespace base {
 
 // A worker thread pool that enforces ordering between sets of tasks. It also
 // allows you to specify what should happen to your tasks on shutdown.
 //
 // To enforce ordering, get a unique sequence token from the pool and post all
 // tasks you want to order with the token. All tasks with the same token are
 // guaranteed to execute serially, though not necessarily on the same thread.
 //
@@ skipping 13 matching lines @@
 //
 // This class is designed to be leaked on shutdown to allow the
 // CONTINUE_ON_SHUTDOWN behavior to be implemented. To enforce the
 // BLOCK_SHUTDOWN behavior, you must call Shutdown() which will wait until
 // the necessary tasks have completed.
 //
 // Implementation note: This does not use a base::WorkerPool since that does
 // not enforce shutdown semantics or allow us to specify how many worker
 // threads to run. For the typical use case of random background work, we don't
 // necessarily want to be super aggressive about creating threads.
-class BASE_EXPORT SequencedWorkerPool {
+class BASE_EXPORT SequencedWorkerPool
+    : public RefCountedThreadSafe<SequencedWorkerPool> {
  public:
   // Defines what should happen to a task posted to the worker pool on shutdown.
   enum WorkerShutdown {
     // Tasks posted with this mode which have not run at shutdown will be
     // deleted rather than run, and any tasks with this mode running at
     // shutdown will be ignored (the worker thread will not be joined).
     //
     // This option provides a nice way to post stuff you don't want blocking
     // shutdown. For example, you might be doing a slow DNS lookup and if it's
     // blocked on the OS, you may not want to stop shutdown, since the result
@@ skipping 20 matching lines @@
     // Generally, this should be used only for user data, for example, a task
     // writing a preference file.
     //
     // If a task is posted during shutdown, it will not get run since the
     // workers may already be stopped. In this case, the post operation will
     // fail (return false) and the task will be deleted.
     BLOCK_SHUTDOWN,
   };
 
   // Opaque identifier that defines sequencing of tasks posted to the worker
-  // pool. See NewSequenceToken().
+  // pool.
   class SequenceToken {
    public:
-    explicit SequenceToken() : id_(0) {}
+    SequenceToken() : id_(0) {}
     ~SequenceToken() {}
 
     bool Equals(const SequenceToken& other) const {
       return id_ == other.id_;
     }
 
    private:
     friend class SequencedWorkerPool;
 
-    SequenceToken(int id) : id_(id) {}
+    explicit SequenceToken(int id) : id_(id) {}
 
     int id_;
   };
 
   // Allows tests to perform certain actions.
   class TestingObserver {
    public:
     virtual ~TestingObserver() {}
     virtual void WillWaitForShutdown() = 0;
   };
 
   // Pass the maximum number of threads (they will be lazily created as needed)
   // and a prefix for the thread name to ad in debugging.
   SequencedWorkerPool(size_t max_threads,
                       const std::string& thread_name_prefix);
-  ~SequencedWorkerPool();
 
   // Returns a unique token that can be used to sequence tasks posted to
   // PostSequencedWorkerTask(). Valid tokens are alwys nonzero.
   SequenceToken GetSequenceToken();
 
   // Returns the sequence token associated with the given name. Calling this
   // function multiple times with the same string will always produce the
   // same sequence token. If the name has not been used before, a new token
   // will be created.
   SequenceToken GetNamedSequenceToken(const std::string& name);
@@ skipping 12 matching lines @@
   // cause nondeterministic crashes because the task could be keeping some
   // objects alive which do work in their destructor, which could voilate the
   // assumptions of the running task.
   //
   // The task will be guaranteed to run to completion before shutdown
   // (BLOCK_SHUTDOWN semantics).
   //
   // Returns true if the task was posted successfully. This may fail during
   // shutdown regardless of the specified ShutdownBehavior.
   bool PostWorkerTask(const tracked_objects::Location& from_here,
-                      const base::Closure& task);
+                      const Closure& task);
 
   // Same as PostWorkerTask but allows specification of the shutdown behavior.
   bool PostWorkerTaskWithShutdownBehavior(
       const tracked_objects::Location& from_here,
-      const base::Closure& task,
+      const Closure& task,
       WorkerShutdown shutdown_behavior);
 
   // Like PostWorkerTask above, but provides sequencing semantics. This means
   // that tasks posted with the same sequence token (see GetSequenceToken())
   // are guaranteed to execute in order. This is useful in cases where you're
   // doing operations that may depend on previous ones, like appending to a
   // file.
   //
   // The task will be guaranteed to run to completion before shutdown
   // (BLOCK_SHUTDOWN semantics).
   //
   // Returns true if the task was posted successfully. This may fail during
   // shutdown regardless of the specified ShutdownBehavior.
   bool PostSequencedWorkerTask(SequenceToken sequence_token,
                                const tracked_objects::Location& from_here,
-                               const base::Closure& task);
+                               const Closure& task);
 
   // Like PostSequencedWorkerTask above, but allows you to specify a named
   // token, which saves an extra call to GetNamedSequenceToken.
   bool PostNamedSequencedWorkerTask(const std::string& token_name,
                                     const tracked_objects::Location& from_here,
-                                    const base::Closure& task);
+                                    const Closure& task);
 
   // Same as PostSequencedWorkerTask but allows specification of the shutdown
   // behavior.
   bool PostSequencedWorkerTaskWithShutdownBehavior(
       SequenceToken sequence_token,
       const tracked_objects::Location& from_here,
-      const base::Closure& task,
+      const Closure& task,
       WorkerShutdown shutdown_behavior);
 
   // Blocks until all pending tasks are complete. This should only be called in
   // unit tests when you want to validate something that should have happened.
   //
   // Note that calling this will not prevent other threads from posting work to
   // the queue while the calling thread is waiting on Flush(). In this case,
   // Flush will return only when there's no more work in the queue. Normally,
   // this doesn't come up sine in a test, all the work is being posted from
   // the main thread.
   void FlushForTesting();
 
   // Implements the worker pool shutdown. This should be called during app
   // shutdown, and will discard/join with appropriate tasks before returning.
   // After this call, subsequent calls to post tasks will fail.
   void Shutdown();
 
   // Called by tests to set the testing observer. This is NULL by default
   // and ownership of the pointer is kept with the caller.
   void SetTestingObserver(TestingObserver* observer);
 
  private:
+  friend class RefCountedThreadSafe<SequencedWorkerPool>;
+
   class Inner;
   class Worker;
 
-  friend class Inner;
-  friend class Worker;
+  ~SequencedWorkerPool();
 
-  scoped_refptr<Inner> inner_;
+  // Avoid pulling in too many headers by putting everything into
+  // |inner_|.
+  const scoped_ptr<Inner> inner_;
 
   DISALLOW_COPY_AND_ASSIGN(SequencedWorkerPool);
 };
 
 }  // namespace base
 
 #endif  // BASE_THREADING_SEQUENCED_WORKER_POOL_H_