Move CancellationFlag and WaitableEvent to the synchronization subdirectory....

base/waitable_event_watcher_posix.cc

Index: base/waitable_event_watcher_posix.cc
===================================================================
--- base/waitable_event_watcher_posix.cc	(revision 70364)
+++ base/waitable_event_watcher_posix.cc	(working copy)
@@ -1,280 +0,0 @@
-// 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/waitable_event_watcher.h"
-
-#include "base/message_loop.h"
-#include "base/synchronization/lock.h"
-#include "base/waitable_event.h"
-
-namespace base {
-
-// -----------------------------------------------------------------------------
-// WaitableEventWatcher (async waits).
-//
-// The basic design is that we add an AsyncWaiter to the wait-list of the event.
-// That AsyncWaiter has a pointer to MessageLoop, and a Task to be posted to it.
-// The MessageLoop ends up running the task, which calls the delegate.
-//
-// Since the wait can be canceled, we have a thread-safe Flag object which is
-// set when the wait has been canceled. At each stage in the above, we check the
-// flag before going onto the next stage. Since the wait may only be canceled in
-// the MessageLoop which runs the Task, we are assured that the delegate cannot
-// be called after canceling...
-
-// -----------------------------------------------------------------------------
-// A thread-safe, reference-counted, write-once flag.
-// -----------------------------------------------------------------------------
-class Flag : public RefCountedThreadSafe<Flag> {
- public:
-  Flag() { flag_ = false; }
-
-  void Set() {
-    AutoLock locked(lock_);
-    flag_ = true;
-  }
-
-  bool value() const {
-    AutoLock locked(lock_);
-    return flag_;
-  }
-
- private:
-  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)
-      : message_loop_(message_loop),
-        cb_task_(task),
-        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_);
-    }
-
-    // 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_;
-  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
-// the event is canceled.
-// -----------------------------------------------------------------------------
-class AsyncCallbackTask : public Task {
- public:
-  AsyncCallbackTask(Flag* flag, WaitableEventWatcher::Delegate* delegate,
-                    WaitableEvent* event)
-      : flag_(flag),
-        delegate_(delegate),
-        event_(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()
-    : event_(NULL),
-      message_loop_(NULL),
-      cancel_flag_(NULL),
-      waiter_(NULL),
-      callback_task_(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()
-  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);
-  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_);
-    return true;
-  }
-
-  message_loop_ = current_ml;
-  current_ml->AddDestructionObserver(this);
-
-  kernel_ = kernel;
-  waiter_ = new AsyncWaiter(current_ml, callback_task_, cancel_flag_);
-  event->Enqueue(waiter_);
-
-  return true;
-}
-
-void WaitableEventWatcher::StopWatching() {
-  delegate_ = NULL;
-
-  if (message_loop_) {
-    message_loop_->RemoveDestructionObserver(this);
-    message_loop_ = NULL;
-  }
-
-  if (!cancel_flag_.get())  // if not currently watching...
-    return;
-
-  if (cancel_flag_->value()) {
-    // In this case, the event has fired, but we haven't figured that out yet.
-    // The WaitableEvent may have been deleted too.
-    cancel_flag_ = NULL;
-    return;
-  }
-
-  if (!kernel_.get()) {
-    // We have no kernel. This means that we never enqueued a Waiter on an
-    // event because the event was already signaled when StartWatching was
-    // called.
-    //
-    // In this case, a task was enqueued on the MessageLoop and will run.
-    // We set the flag in case the task hasn't yet run. The flag will stop the
-    // delegate getting called. If the task has run then we have the last
-    // reference to the flag and it will be deleted immedately after.
-    cancel_flag_->Set();
-    cancel_flag_ = NULL;
-    return;
-  }
-
-  AutoLock locked(kernel_->lock_);
-  // We have a lock on the kernel. No one else can signal the event while we
-  // have it.
-
-  // We have a possible ABA issue here. If Dequeue was to compare only the
-  // pointer values then it's possible that the AsyncWaiter could have been
-  // fired, freed and the memory reused for a different Waiter which was
-  // enqueued in the same wait-list. We would think that that waiter was our
-  // AsyncWaiter and remove it.
-  //
-  // To stop this, Dequeue also takes a tag argument which is passed to the
-  // virtual Compare function before the two are considered a match. So we need
-  // 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_;
-    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;
-
-  // If the waiter has already run then the task has been enqueued. If the Task
-  // hasn't yet run, the flag will stop the delegate from getting called. (This
-  // is thread safe because one may only delete a Handle from the MessageLoop
-  // thread.)
-  //
-  // If the delegate has already been called then we have nothing to do. The
-  // task has been deleted by the MessageLoop.
-}
-
-WaitableEvent* WaitableEventWatcher::GetWatchedEvent() {
-  if (!cancel_flag_.get())
-    return NULL;
-
-  if (cancel_flag_->value())
-    return NULL;
-
-  return event_;
-}
-
-// -----------------------------------------------------------------------------
-// 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