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// Copyright (c) 2012 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.
// This module provides a way to monitor a file or directory for changes.
#include <memory>
#include "base/base_export.h"
#include "base/callback.h"
#include "base/files/file_path.h"
#include "base/macros.h"
#include "base/memory/ref_counted.h"
#include "base/sequence_checker.h"
#include "base/sequenced_task_runner.h"
#if !defined(STARBOARD)
namespace base {
// This class lets you register interest in changes on a FilePath.
// The callback will get called whenever the file or directory referenced by the
// FilePath is changed, including created or deleted. Due to limitations in the
// underlying OS APIs, FilePathWatcher has slightly different semantics on OS X
// than on Windows or Linux. FilePathWatcher on Linux and Windows will detect
// modifications to files in a watched directory. FilePathWatcher on Mac will
// detect the creation and deletion of files in a watched directory, but will
// not detect modifications to those files. See for
// details.
// Must be destroyed on the sequence that invokes Watch().
class BASE_EXPORT FilePathWatcher {
// Callback type for Watch(). |path| points to the file that was updated,
// and |error| is true if the platform specific code detected an error. In
// that case, the callback won't be invoked again.
typedef base::Callback<void(const FilePath& path, bool error)> Callback;
// Used internally to encapsulate different members on different platforms.
class PlatformDelegate {
virtual ~PlatformDelegate();
// Start watching for the given |path| and notify |delegate| about changes.
virtual bool Watch(const FilePath& path,
bool recursive,
const Callback& callback) WARN_UNUSED_RESULT = 0;
// Stop watching. This is called from FilePathWatcher's dtor in order to
// allow to shut down properly while the object is still alive.
virtual void Cancel() = 0;
friend class FilePathWatcher;
scoped_refptr<SequencedTaskRunner> task_runner() const {
return task_runner_;
void set_task_runner(scoped_refptr<SequencedTaskRunner> runner) {
task_runner_ = std::move(runner);
// Must be called before the PlatformDelegate is deleted.
void set_cancelled() {
cancelled_ = true;
bool is_cancelled() const {
return cancelled_;
scoped_refptr<SequencedTaskRunner> task_runner_;
bool cancelled_;
// Returns true if the platform and OS version support recursive watches.
static bool RecursiveWatchAvailable();
// Invokes |callback| whenever updates to |path| are detected. This should be
// called at most once. Set |recursive| to true to watch |path| and its
// children. The callback will be invoked on the same sequence. Returns true
// on success.
// On POSIX, this must be called from a thread that supports
// FileDescriptorWatcher.
// Recursive watch is not supported on all platforms and file systems.
// Watch() will return false in the case of failure.
bool Watch(const FilePath& path, bool recursive, const Callback& callback);
std::unique_ptr<PlatformDelegate> impl_;
SequenceChecker sequence_checker_;
} // namespace base
#endif // !defined(STARBOARD)