waitable_event_watcher_posix.cc | Explore in Territory

// Copyright 2012 The Chromium Authors
// 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 <utility>

#include "base/check.h"
#include "base/functional/bind.h"
#include "base/synchronization/lock.h"
#include "base/synchronization/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 SequencedTaskRunner, and a Task to be
// posted to it. The task ends up calling the callback when it runs on the
// sequence.
//
// 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 sequence which runs the Task, we are assured that the callback cannot be
// called after canceling...

// -----------------------------------------------------------------------------
// A thread-safe, reference-counted, write-once flag.
// -----------------------------------------------------------------------------
class Flag : public RefCountedThreadSafe<Flag> { … };

// -----------------------------------------------------------------------------
// This is an asynchronous waiter which posts a task to a SequencedTaskRunner
// when fired. An AsyncWaiter may only be in a single wait-list.
// -----------------------------------------------------------------------------
class AsyncWaiter : public WaitableEvent::Waiter { … };

// -----------------------------------------------------------------------------
// For async waits we need to run a callback on a sequence. We do this by
// posting an AsyncCallbackHelper task, which calls the callback and keeps track
// of when the event is canceled.
// -----------------------------------------------------------------------------
void AsyncCallbackHelper(Flag* flag,
                         WaitableEventWatcher::EventCallback callback,
                         WaitableEvent* event) { … }

WaitableEventWatcher::WaitableEventWatcher() { … }

WaitableEventWatcher::~WaitableEventWatcher() { … }

// -----------------------------------------------------------------------------
// 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,
    EventCallback callback,
    scoped_refptr<SequencedTaskRunner> task_runner) { … }

void WaitableEventWatcher::StopWatching() { … }

}  // namespace base
chromium/base/synchronization/waitable_event_watcher_posix.cc
