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// 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 "base/files/file_descriptor_watcher_posix.h"
#include "base/bind.h"
#include "base/lazy_instance.h"
#include "base/logging.h"
#include "base/memory/ptr_util.h"
#include "base/sequenced_task_runner.h"
#include "base/single_thread_task_runner.h"
#include "base/threading/sequenced_task_runner_handle.h"
#include "base/threading/thread_checker.h"
#include "base/threading/thread_local.h"
namespace base {
namespace {
// MessageLoopForIO used to watch file descriptors for which callbacks are
// registered from a given thread.
LazyInstance<ThreadLocalPointer<MessageLoopForIO>>::Leaky
tls_message_loop_for_io = LAZY_INSTANCE_INITIALIZER;
} // namespace
FileDescriptorWatcher::Controller::~Controller() {
DCHECK(sequence_checker_.CalledOnValidSequence());
// Delete |watcher_| on the MessageLoopForIO.
//
// If the MessageLoopForIO is deleted before Watcher::StartWatching() runs,
// |watcher_| is leaked. If the MessageLoopForIO is deleted after
// Watcher::StartWatching() runs but before the DeleteSoon task runs,
// |watcher_| is deleted from Watcher::WillDestroyCurrentMessageLoop().
message_loop_for_io_task_runner_->DeleteSoon(FROM_HERE, watcher_.release());
// Since WeakPtrs are invalidated by the destructor, RunCallback() won't be
// invoked after this returns.
}
class FileDescriptorWatcher::Controller::Watcher
: public MessageLoopForIO::Watcher,
public MessageLoop::DestructionObserver {
public:
Watcher(WeakPtr<Controller> controller, MessageLoopForIO::Mode mode, int fd);
~Watcher() override;
void StartWatching();
private:
friend class FileDescriptorWatcher;
// MessageLoopForIO::Watcher:
void OnFileCanReadWithoutBlocking(int fd) override;
void OnFileCanWriteWithoutBlocking(int fd) override;
// MessageLoop::DestructionObserver:
void WillDestroyCurrentMessageLoop() override;
// Used to instruct the MessageLoopForIO to stop watching the file descriptor.
MessageLoopForIO::FileDescriptorWatcher file_descriptor_watcher_;
// Runs tasks on the sequence on which this was instantiated (i.e. the
// sequence on which the callback must run).
const scoped_refptr<SequencedTaskRunner> callback_task_runner_ =
SequencedTaskRunnerHandle::Get();
// The Controller that created this Watcher.
WeakPtr<Controller> controller_;
// Whether this Watcher is notified when |fd_| becomes readable or writable
// without blocking.
const MessageLoopForIO::Mode mode_;
// The watched file descriptor.
const int fd_;
// Except for the constructor, every method of this class must run on the same
// MessageLoopForIO thread.
ThreadChecker thread_checker_;
// Whether this Watcher was registered as a DestructionObserver on the
// MessageLoopForIO thread.
bool registered_as_destruction_observer_ = false;
DISALLOW_COPY_AND_ASSIGN(Watcher);
};
FileDescriptorWatcher::Controller::Watcher::Watcher(
WeakPtr<Controller> controller,
MessageLoopForIO::Mode mode,
int fd)
: file_descriptor_watcher_(FROM_HERE),
controller_(controller),
mode_(mode),
fd_(fd) {
DCHECK(callback_task_runner_);
thread_checker_.DetachFromThread();
}
FileDescriptorWatcher::Controller::Watcher::~Watcher() {
DCHECK(thread_checker_.CalledOnValidThread());
MessageLoopForIO::current()->RemoveDestructionObserver(this);
}
void FileDescriptorWatcher::Controller::Watcher::StartWatching() {
DCHECK(thread_checker_.CalledOnValidThread());
MessageLoopForIO::current()->WatchFileDescriptor(
fd_, false, mode_, &file_descriptor_watcher_, this);
if (!registered_as_destruction_observer_) {
MessageLoopForIO::current()->AddDestructionObserver(this);
registered_as_destruction_observer_ = true;
}
}
void FileDescriptorWatcher::Controller::Watcher::OnFileCanReadWithoutBlocking(
int fd) {
DCHECK_EQ(fd_, fd);
DCHECK_EQ(MessageLoopForIO::WATCH_READ, mode_);
DCHECK(thread_checker_.CalledOnValidThread());
// Run the callback on the sequence on which the watch was initiated.
callback_task_runner_->PostTask(FROM_HERE,
Bind(&Controller::RunCallback, controller_));
}
void FileDescriptorWatcher::Controller::Watcher::OnFileCanWriteWithoutBlocking(
int fd) {
DCHECK_EQ(fd_, fd);
DCHECK_EQ(MessageLoopForIO::WATCH_WRITE, mode_);
DCHECK(thread_checker_.CalledOnValidThread());
// Run the callback on the sequence on which the watch was initiated.
callback_task_runner_->PostTask(FROM_HERE,
Bind(&Controller::RunCallback, controller_));
}
void FileDescriptorWatcher::Controller::Watcher::
WillDestroyCurrentMessageLoop() {
DCHECK(thread_checker_.CalledOnValidThread());
// A Watcher is owned by a Controller. When the Controller is deleted, it
// transfers ownership of the Watcher to a delete task posted to the
// MessageLoopForIO. If the MessageLoopForIO is deleted before the delete task
// runs, the following line takes care of deleting the Watcher.
delete this;
}
FileDescriptorWatcher::Controller::Controller(MessageLoopForIO::Mode mode,
int fd,
const Closure& callback)
: callback_(callback),
message_loop_for_io_task_runner_(
tls_message_loop_for_io.Get().Get()->task_runner()),
weak_factory_(this) {
DCHECK(!callback_.is_null());
DCHECK(message_loop_for_io_task_runner_);
watcher_ = MakeUnique<Watcher>(weak_factory_.GetWeakPtr(), mode, fd);
StartWatching();
}
void FileDescriptorWatcher::Controller::StartWatching() {
DCHECK(sequence_checker_.CalledOnValidSequence());
// It is safe to use Unretained() below because |watcher_| can only be deleted
// by a delete task posted to |message_loop_for_io_task_runner_| by this
// Controller's destructor. Since this delete task hasn't been posted yet, it
// can't run before the task posted below.
message_loop_for_io_task_runner_->PostTask(
FROM_HERE, Bind(&Watcher::StartWatching, Unretained(watcher_.get())));
}
void FileDescriptorWatcher::Controller::RunCallback() {
DCHECK(sequence_checker_.CalledOnValidSequence());
WeakPtr<Controller> weak_this = weak_factory_.GetWeakPtr();
callback_.Run();
// If |this| wasn't deleted, re-enable the watch.
if (weak_this)
StartWatching();
}
FileDescriptorWatcher::FileDescriptorWatcher(
MessageLoopForIO* message_loop_for_io) {
DCHECK(message_loop_for_io);
DCHECK(!tls_message_loop_for_io.Get().Get());
tls_message_loop_for_io.Get().Set(message_loop_for_io);
}
FileDescriptorWatcher::~FileDescriptorWatcher() {
tls_message_loop_for_io.Get().Set(nullptr);
}
std::unique_ptr<FileDescriptorWatcher::Controller>
FileDescriptorWatcher::WatchReadable(int fd, const Closure& callback) {
return WrapUnique(new Controller(MessageLoopForIO::WATCH_READ, fd, callback));
}
std::unique_ptr<FileDescriptorWatcher::Controller>
FileDescriptorWatcher::WatchWritable(int fd, const Closure& callback) {
return WrapUnique(
new Controller(MessageLoopForIO::WATCH_WRITE, fd, callback));
}
} // namespace base
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