Revert 51312 - Disk cache: Switch the disk cache to use the cache_thread....

net/disk_cache/in_flight_io.h

-// Copyright (c) 2006-2010 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 NET_DISK_CACHE_IN_FLIGHT_IO_H_
-#define NET_DISK_CACHE_IN_FLIGHT_IO_H_
-
-#include <set>
-
-#include "base/message_loop.h"
-#include "base/waitable_event.h"
-
-namespace disk_cache {
-
-class InFlightIO;
-
-// This class represents a single asynchronous IO operation while it is being
-// bounced between threads.
-class BackgroundIO : public base::RefCountedThreadSafe<BackgroundIO> {
- public:
-  // Other than the actual parameters for the IO operation (including the
-  // |callback| that must be notified at the end), we need the controller that
-  // is keeping track of all operations. When done, we notify the controller
-  // (we do NOT invoke the callback), in the worker thead that completed the
-  // operation.
-  explicit BackgroundIO(InFlightIO* controller)
-      : controller_(controller), result_(-1), io_completed_(true, false) {}
-
-  // This method signals the controller that this operation is finished, in the
-  // original thread (presumably the IO-Thread). In practice, this is a
-  // RunableMethod that allows cancellation.
-  void OnIOSignalled();
-
-  // Allows the cancellation of the task to notify the controller (step number 8
-  // in the diagram below). In practice, if the controller waits for the
-  // operation to finish it doesn't have to wait for the final task to be
-  // processed by the message loop so calling this method prevents its delivery.
-  // Note that this method is not intended to cancel the actual IO operation or
-  // to prevent the first notification to take place (OnIOComplete).
-  void Cancel();
-
-  int result() { return result_; }
-
-  base::WaitableEvent* io_completed() {
-    return &io_completed_;
-  }
-
- protected:
-  virtual ~BackgroundIO() {}
-
-  InFlightIO* controller_;  // The controller that tracks all operations.
-  int result_;  // Final operation result.
-
- private:
-  friend class base::RefCountedThreadSafe<BackgroundIO>;
-
-  // Notifies the controller about the end of the operation, from the background
-  // thread.
-  void NotifyController();
-
-  // An event to signal when the operation completes.
-  base::WaitableEvent io_completed_;
-
-  DISALLOW_COPY_AND_ASSIGN(BackgroundIO);
-};
-
-// This class keeps track of asynchronous IO operations. A single instance
-// of this class is meant to be used to start an asynchronous operation (using
-// PostXX, exposed by a derived class). This class will post the operation to a
-// worker thread, hanlde the notification when the operation finishes and
-// perform the callback on the same thread that was used to start the operation.
-//
-// The regular sequence of calls is:
-//                 Thread_1                          Worker_thread
-//    1.     DerivedInFlightIO::PostXX()
-//    2.                         -> PostTask ->
-//    3.    InFlightIO::OnOperationPosted()
-//    4.                                        DerivedBackgroundIO::XX()
-//    5.                                         IO operation completes
-//    6.                                       InFlightIO::OnIOComplete()
-//    7.                         <- PostTask <-
-//    8.  BackgroundIO::OnIOSignalled()
-//    9.  InFlightIO::InvokeCallback()
-//   10. DerivedInFlightIO::OnOperationComplete()
-//   11.       invoke callback
-//
-// Shutdown is a special case that is handled though WaitForPendingIO() instead
-// of just waiting for step 7.
-class InFlightIO {
- public:
-  InFlightIO() : callback_thread_(MessageLoop::current()) {}
-  virtual ~InFlightIO() {}
-
-  // Blocks the current thread until all IO operations tracked by this object
-  // complete.
-  void WaitForPendingIO();
-
-  // Called on a background thread when |operation| completes.
-  void OnIOComplete(BackgroundIO* operation);
-
-  // Invokes the users' completion callback at the end of the IO operation.
-  // |cancel_task| is true if the actual task posted to the thread is still
-  // queued (because we are inside WaitForPendingIO), and false if said task is
-  // the one performing the call.
-  void InvokeCallback(BackgroundIO* operation, bool cancel_task);
-
- protected:
-  // This method is called to signal the completion of the |operation|. |cancel|
-  // is true if the operation is being cancelled. This method is called on the
-  // thread that created this object.
-  virtual void OnOperationComplete(BackgroundIO* operation, bool cancel) = 0;
-
-  // Signals this object that the derived class just posted the |operation| to
-  // be executed on a background thread. This method must be called on the same
-  // thread used to create this object.
-  void OnOperationPosted(BackgroundIO* operation);
-
- private:
-  typedef std::set<scoped_refptr<BackgroundIO> > IOList;
-
-  IOList io_list_;  // List of pending, in-flight io operations.
-  MessageLoop* callback_thread_;
-  DISALLOW_COPY_AND_ASSIGN(InFlightIO);
-};
-
-}  // namespace disk_cache
-
-#endif  // NET_DISK_CACHE_IN_FLIGHT_IO_H_