Remove custom Task implementations in base.

base/synchronization/waitable_event_watcher_posix.cc

 // Copyright (c) 2011 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 "base/synchronization/waitable_event_watcher.h"
 
+#include "base/bind.h"
 #include "base/location.h"
 #include "base/message_loop.h"
 #include "base/synchronization/lock.h"
 #include "base/synchronization/waitable_event.h"
 
 namespace base {
 
 // -----------------------------------------------------------------------------
 // WaitableEventWatcher (async waits).
 //
@@ skipping 28 matching lines @@
   mutable Lock lock_;
   bool flag_;
 };
 
 // -----------------------------------------------------------------------------
 // This is an asynchronous waiter which posts a task to a MessageLoop when
 // fired. An AsyncWaiter may only be in a single wait-list.
 // -----------------------------------------------------------------------------
 class AsyncWaiter : public WaitableEvent::Waiter {
  public:
-  AsyncWaiter(MessageLoop* message_loop, Task* task, Flag* flag)
+  AsyncWaiter(MessageLoop* message_loop,
+              const base::Closure& callback,
+              Flag* flag)
       : message_loop_(message_loop),
-        cb_task_(task),
+        callback_(callback),
         flag_(flag) { }
 
   bool Fire(WaitableEvent* event) {
-    if (flag_->value()) {
-      // If the callback has been canceled, we don't enqueue the task, we just
-      // delete it instead.
-      delete cb_task_;
-    } else {
-      message_loop_->PostTask(FROM_HERE, cb_task_);
+    // Post the callback if we haven't been cancelled.
+    if (!flag_->value()) {
+      message_loop_->PostTask(FROM_HERE, callback_);
     }
 
     // We are removed from the wait-list by the WaitableEvent itself. It only
     // remains to delete ourselves.
     delete this;
 
     // We can always return true because an AsyncWaiter is never in two
     // different wait-lists at the same time.
     return true;
   }
 
   // See StopWatching for discussion
   bool Compare(void* tag) {
     return tag == flag_.get();
   }
 
  private:
   MessageLoop *const message_loop_;
-  Task *const cb_task_;
+  base::Closure callback_;
   scoped_refptr<Flag> flag_;
 };
 
 // -----------------------------------------------------------------------------
 // For async waits we need to make a callback in a MessageLoop thread. We do
-// this by posting this task, which calls the delegate and keeps track of when
+// this by posting a callback, which calls the delegate and keeps track of when
 // the event is canceled.
 // -----------------------------------------------------------------------------
-class AsyncCallbackTask : public Task {
- public:
-  AsyncCallbackTask(Flag* flag, WaitableEventWatcher::Delegate* delegate,
-                    WaitableEvent* event)
-      : flag_(flag),
-        delegate_(delegate),
-        event_(event) {
+void AsyncCallbackHelper(scoped_refptr<Flag> flag,

[willchan no longer on Chromium, 2011/11/23 18:15:46]

Do Flag* instead of scoped_refptr<Flag>.

The type matters more at the base::Bind() callsite, not the function prototype.
This is because base::Bind() will be copying the argument into a storage
container for when Run() gets called. This storage must be a scoped_refptr.
However, when Run() is actually called, we'll do a scoped_refptr<T> to T*
implicit conversion, due to the operator* operator in scoped_refptr. Therefore,
there's no need to make the function prototype be scoped_refptr<T>, because
that'll just result in an extra unnecessary AddRef()/Release() pair.

[dcheng, 2011/11/23 18:47:49]

Done, I wasn't sure if base::Bind() would automatically do the right thing if
the underlying type is refcounted.

+                         WaitableEventWatcher::Delegate* delegate,
+                         WaitableEvent* event) {
+  // Runs in MessageLoop thread.
+  if (!flag->value()) {
+    // This is to let the WaitableEventWatcher know that the event has occured
+    // because it needs to be able to return NULL from GetWatchedObject
+    flag->Set();
+    delegate->OnWaitableEventSignaled(event);
   }
-
-  void Run() {
-    // Runs in MessageLoop thread.
-    if (!flag_->value()) {
-      // This is to let the WaitableEventWatcher know that the event has occured
-      // because it needs to be able to return NULL from GetWatchedObject
-      flag_->Set();
-      delegate_->OnWaitableEventSignaled(event_);
-    }
-
-    // We are deleted by the MessageLoop
-  }
-
- private:
-  scoped_refptr<Flag> flag_;
-  WaitableEventWatcher::Delegate *const delegate_;
-  WaitableEvent *const event_;
-};
+}
 
 WaitableEventWatcher::WaitableEventWatcher()
     : message_loop_(NULL),
       cancel_flag_(NULL),
       waiter_(NULL),
-      callback_task_(NULL),
       event_(NULL),
       delegate_(NULL) {
 }
 
 WaitableEventWatcher::~WaitableEventWatcher() {
   StopWatching();
 }
 
 // -----------------------------------------------------------------------------
 // The Handle is how the user cancels a wait. After deleting the Handle we
 // insure that the delegate cannot be called.
 // -----------------------------------------------------------------------------
 bool WaitableEventWatcher::StartWatching
     (WaitableEvent* event, WaitableEventWatcher::Delegate* delegate) {
   MessageLoop *const current_ml = MessageLoop::current();
   DCHECK(current_ml) << "Cannot create WaitableEventWatcher without a "
                         "current MessageLoop";
 
   // A user may call StartWatching from within the callback function. In this
   // case, we won't know that we have finished watching, expect that the Flag
-  // will have been set in AsyncCallbackTask::Run()
+  // will have been set in AsyncCallbackHelper().
   if (cancel_flag_.get() && cancel_flag_->value()) {
     if (message_loop_) {
       message_loop_->RemoveDestructionObserver(this);
       message_loop_ = NULL;
     }
 
     cancel_flag_ = NULL;
   }
 
   DCHECK(!cancel_flag_.get()) << "StartWatching called while still watching";
 
   cancel_flag_ = new Flag;
-  callback_task_ = new AsyncCallbackTask(cancel_flag_, delegate, event);
+  callback_ = base::Bind(&AsyncCallbackHelper, cancel_flag_, delegate, event);
   WaitableEvent::WaitableEventKernel* kernel = event->kernel_.get();
 
   AutoLock locked(kernel->lock_);
 
   delegate_ = delegate;
   event_ = event;
 
   if (kernel->signaled_) {
     if (!kernel->manual_reset_)
       kernel->signaled_ = false;
 
     // No hairpinning - we can't call the delegate directly here. We have to
     // enqueue a task on the MessageLoop as normal.
-    current_ml->PostTask(FROM_HERE, callback_task_);
+    current_ml->PostTask(FROM_HERE, callback_);
     return true;
   }
 
   message_loop_ = current_ml;
   current_ml->AddDestructionObserver(this);
 
   kernel_ = kernel;
-  waiter_ = new AsyncWaiter(current_ml, callback_task_, cancel_flag_);
+  waiter_ = new AsyncWaiter(current_ml, callback_, cancel_flag_);
   event->Enqueue(waiter_);
 
   return true;
 }
 
 void WaitableEventWatcher::StopWatching() {
   delegate_ = NULL;
 
   if (message_loop_) {
     message_loop_->RemoveDestructionObserver(this);
@@ skipping 39 matching lines @@
   // a tag which is good for the lifetime of this handle: the Flag. Since we
   // have a reference to the Flag, its memory cannot be reused while this object
   // still exists. So if we find a waiter with the correct pointer value, and
   // which shares a Flag pointer, we have a real match.
   if (kernel_->Dequeue(waiter_, cancel_flag_.get())) {
     // Case 2: the waiter hasn't been signaled yet; it was still on the wait
     // list. We've removed it, thus we can delete it and the task (which cannot
     // have been enqueued with the MessageLoop because the waiter was never
     // signaled)
     delete waiter_;
-    delete callback_task_;
+    callback_.Reset();
     cancel_flag_ = NULL;
     return;
   }
 
   // Case 3: the waiter isn't on the wait-list, thus it was signaled. It may
   // not have run yet, so we set the flag to tell it not to bother enqueuing the
   // task on the MessageLoop, but to delete it instead. The Waiter deletes
   // itself once run.
   cancel_flag_->Set();
   cancel_flag_ = NULL;
@@ skipping 20 matching lines @@
 // -----------------------------------------------------------------------------
 // This is called when the MessageLoop which the callback will be run it is
 // deleted. We need to cancel the callback as if we had been deleted, but we
 // will still be deleted at some point in the future.
 // -----------------------------------------------------------------------------
 void WaitableEventWatcher::WillDestroyCurrentMessageLoop() {
   StopWatching();
 }
 
 }  // namespace base