[SyncFS] Introduce CallbackTracker to handle callback abortion

chrome/browser/sync_file_system/drive_backend/callback_tracker.h

+// Copyright 2014 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 CHROME_BROWSER_SYNC_FILE_SYSTEM_DRIVE_BACKEND_CALLBACK_TRACKER_H_
+#define CHROME_BROWSER_SYNC_FILE_SYSTEM_DRIVE_BACKEND_CALLBACK_TRACKER_H_
+
+#include <map>
+
+#include "base/bind.h"
+#include "base/callback_forward.h"
+#include "base/memory/weak_ptr.h"
+#include "chrome/browser/sync_file_system/drive_backend/callback_tracker_internal.h"
+
+namespace sync_file_system {
+namespace drive_backend {
+
+// A helper class to ensure one-shot callback to be called exactly once.
+//
+// Usage:
+//   class Foo {
+//    private:
+//     CallbackTracker callback_tracker_;
+//   };
+//
+//   void DoSomethingAsync(const SomeCallbackType& callback) {
+//     base::Closure abort_case_handler = base::Bind(callback, ABORT_ERROR);
+//
+//     SomeCallbackType wrapped_callback =
+//         callback_tracker_.Register(
+//             abort_case_handler, callback);
+//
+//     // The body of the operation goes here.
+//   }
+class CallbackTracker {
+ public:
+  typedef std::map<internal::AbortHelper*, base::Closure> AbortClosureByHelper;
+
+  CallbackTracker();
+  ~CallbackTracker();
+
+  // Returns a wrapped callback.
+  // Upon AbortAll() call, CallbackTracker invokes |abort_closure| and voids all
+  // wrapped callbacks returned by Register().
+  // Invocation of the wrapped callback unregisters |callback| from
+  // CallbackTracker.
+  template <typename T>
+  base::Callback<T> Register(const base::Closure& abort_closure,
+                             const base::Callback<T>& callback) {
+    internal::AbortHelper* helper = new internal::AbortHelper(this);
+    helpers_[helper] = abort_closure;
+    return base::Bind(&internal::InvokeAndInvalidateHelper<T>::Run,
+                      helper->AsWeakPtr(), callback);
+  }
+
+  void AbortAll();
+
+ private:
+  friend class internal::AbortHelper;
+
+  scoped_ptr<internal::AbortHelper> PassAbortHelper(
+      internal::AbortHelper* helper);
+
+  AbortClosureByHelper helpers_;  // Owns AbortHelpers.
+
+  DISALLOW_COPY_AND_ASSIGN(CallbackTracker);
+};
+
+}  // namespace drive_backend
+}  // namespace sync_file_system
+
+#endif  // CHROME_BROWSER_SYNC_FILE_SYSTEM_DRIVE_BACKEND_CALLBACK_TRACKER_H_