blob: 6857d370946c686e8bca81948e7b7add617ffd97 [file] [log] [blame]
// 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.
#include <set>
#include "base/logging.h"
#include "base/macros.h"
#include "base/memory/ref_counted.h"
#include "base/synchronization/lock.h"
#include "base/synchronization/waitable_event.h"
namespace base {
class SequencedTaskRunner;
} // namespace base
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> {
// 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);
// This method signals the controller that this operation is finished, in the
// original 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_;
virtual ~BackgroundIO();
// Notifies the controller about the end of the operation, from the background
// thread.
void NotifyController();
int result_; // Final operation result.
friend class base::RefCountedThreadSafe<BackgroundIO>;
// An event to signal when the operation completes.
base::WaitableEvent io_completed_;
InFlightIO* controller_; // The controller that tracks all operations.
base::Lock controller_lock_; // A lock protecting clearing of controller_.
// 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 {
virtual ~InFlightIO();
// Blocks the current thread until all IO operations tracked by this object
// complete.
void WaitForPendingIO();
// Drops current pending operations without waiting for them to complete.
void DropPendingIO();
// 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);
// 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);
typedef std::set<scoped_refptr<BackgroundIO> > IOList;
IOList io_list_; // List of pending, in-flight io operations.
scoped_refptr<base::SequencedTaskRunner> callback_task_runner_;
bool running_; // True after the first posted operation completes.
bool single_thread_ = false; // True if we only have one thread.
} // namespace disk_cache