blob: aa4457904b88f54a88a49a695903a61c88ce3fa6 [file] [log] [blame]
// Copyright 2016 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 <memory>
#include "base/base_export.h"
#include "base/callback.h"
#include "base/macros.h"
#include "base/memory/ref_counted.h"
#include "base/memory/weak_ptr.h"
#include "base/message_loop/message_loop.h"
#include "base/message_loop/message_pump_for_io.h"
#include "base/sequence_checker.h"
namespace base {
class SingleThreadTaskRunner;
// The FileDescriptorWatcher API allows callbacks to be invoked when file
// descriptors are readable or writable without blocking.
// To enable this API in unit tests, use a ScopedTaskEnvironment with
// MainThreadType::IO.
// Note: Prefer FileDescriptorWatcher to MessageLoopForIO::WatchFileDescriptor()
// for non-critical IO. FileDescriptorWatcher works on threads/sequences without
// MessagePumps but involves going through the task queue after being notified
// by the OS (a desirablable property for non-critical IO that shouldn't preempt
// the main queue).
class BASE_EXPORT FileDescriptorWatcher {
// Instantiated and returned by WatchReadable() or WatchWritable(). The
// constructor registers a callback to be invoked when a file descriptor is
// readable or writable without blocking and the destructor unregisters it.
class Controller {
// Unregisters the callback registered by the constructor.
friend class FileDescriptorWatcher;
class Watcher;
// Registers |callback| to be invoked when |fd| is readable or writable
// without blocking (depending on |mode|).
Controller(MessagePumpForIO::Mode mode, int fd, const Closure& callback);
// Starts watching the file descriptor.
void StartWatching();
// Runs |callback_|.
void RunCallback();
// The callback to run when the watched file descriptor is readable or
// writable without blocking.
Closure callback_;
// TaskRunner associated with the MessageLoopForIO that watches the file
// descriptor.
const scoped_refptr<SingleThreadTaskRunner>
// Notified by the MessageLoopForIO associated with
// |message_loop_for_io_task_runner_| when the watched file descriptor is
// readable or writable without blocking. Posts a task to run RunCallback()
// on the sequence on which the Controller was instantiated. When the
// Controller is deleted, ownership of |watcher_| is transfered to a delete
// task posted to the MessageLoopForIO. This ensures that |watcher_| isn't
// deleted while it is being used by the MessageLoopForIO.
std::unique_ptr<Watcher> watcher_;
// Validates that the Controller is used on the sequence on which it was
// instantiated.
SequenceChecker sequence_checker_;
WeakPtrFactory<Controller> weak_factory_;
// Registers |message_loop_for_io| to watch file descriptors for which
// callbacks are registered from the current thread via WatchReadable() or
// WatchWritable(). |message_loop_for_io| may run on another thread. The
// constructed FileDescriptorWatcher must not outlive |message_loop_for_io|.
FileDescriptorWatcher(MessageLoopForIO* message_loop_for_io);
// Registers |callback| to be posted on the current sequence when |fd| is
// readable or writable without blocking. |callback| is unregistered when the
// returned Controller is deleted (deletion must happen on the current
// sequence). To call these methods, a FileDescriptorWatcher must have been
// instantiated on the current thread and SequencedTaskRunnerHandle::IsSet()
// must return true (these conditions are met at least on all TaskScheduler
// threads as well as on threads backed by a MessageLoopForIO).
static std::unique_ptr<Controller> WatchReadable(int fd,
const Closure& callback);
static std::unique_ptr<Controller> WatchWritable(int fd,
const Closure& callback);
} // namespace base