293 lines
9.9 KiB
C++
293 lines
9.9 KiB
C++
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// Copyright (c) 2011 The Chromium Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file.
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#include "base/files/file_path_watcher.h"
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#include "base/bind.h"
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#include "base/file_util.h"
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#include "base/files/file_path.h"
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#include "base/logging.h"
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#include "base/memory/ref_counted.h"
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#include "base/message_loop/message_loop_proxy.h"
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#include "base/time/time.h"
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#include "base/win/object_watcher.h"
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namespace base {
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namespace {
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class FilePathWatcherImpl : public FilePathWatcher::PlatformDelegate,
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public base::win::ObjectWatcher::Delegate,
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public MessageLoop::DestructionObserver {
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public:
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FilePathWatcherImpl()
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: handle_(INVALID_HANDLE_VALUE),
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recursive_watch_(false) {}
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// FilePathWatcher::PlatformDelegate overrides.
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virtual bool Watch(const FilePath& path,
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bool recursive,
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const FilePathWatcher::Callback& callback) OVERRIDE;
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virtual void Cancel() OVERRIDE;
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// Deletion of the FilePathWatcher will call Cancel() to dispose of this
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// object in the right thread. This also observes destruction of the required
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// cleanup thread, in case it quits before Cancel() is called.
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virtual void WillDestroyCurrentMessageLoop() OVERRIDE;
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// Callback from MessageLoopForIO.
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virtual void OnObjectSignaled(HANDLE object);
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private:
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virtual ~FilePathWatcherImpl() {}
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// Setup a watch handle for directory |dir|. Set |recursive| to true to watch
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// the directory sub trees. Returns true if no fatal error occurs. |handle|
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// will receive the handle value if |dir| is watchable, otherwise
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// INVALID_HANDLE_VALUE.
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static bool SetupWatchHandle(const FilePath& dir,
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bool recursive,
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HANDLE* handle) WARN_UNUSED_RESULT;
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// (Re-)Initialize the watch handle.
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bool UpdateWatch() WARN_UNUSED_RESULT;
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// Destroy the watch handle.
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void DestroyWatch();
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// Cleans up and stops observing the |message_loop_| thread.
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void CancelOnMessageLoopThread() OVERRIDE;
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// Callback to notify upon changes.
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FilePathWatcher::Callback callback_;
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// Path we're supposed to watch (passed to callback).
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FilePath target_;
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// Handle for FindFirstChangeNotification.
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HANDLE handle_;
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// ObjectWatcher to watch handle_ for events.
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base::win::ObjectWatcher watcher_;
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// Set to true to watch the sub trees of the specified directory file path.
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bool recursive_watch_;
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// Keep track of the last modified time of the file. We use nulltime
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// to represent the file not existing.
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base::Time last_modified_;
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// The time at which we processed the first notification with the
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// |last_modified_| time stamp.
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base::Time first_notification_;
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DISALLOW_COPY_AND_ASSIGN(FilePathWatcherImpl);
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};
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bool FilePathWatcherImpl::Watch(const FilePath& path,
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bool recursive,
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const FilePathWatcher::Callback& callback) {
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DCHECK(target_.value().empty()); // Can only watch one path.
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set_message_loop(base::MessageLoopProxy::current());
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callback_ = callback;
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target_ = path;
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recursive_watch_ = recursive;
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MessageLoop::current()->AddDestructionObserver(this);
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if (!UpdateWatch())
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return false;
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watcher_.StartWatching(handle_, this);
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return true;
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}
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void FilePathWatcherImpl::Cancel() {
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if (callback_.is_null()) {
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// Watch was never called, or the |message_loop_| has already quit.
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set_cancelled();
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return;
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}
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// Switch to the file thread if necessary so we can stop |watcher_|.
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if (!message_loop()->BelongsToCurrentThread()) {
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message_loop()->PostTask(FROM_HERE,
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base::Bind(&FilePathWatcher::CancelWatch,
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make_scoped_refptr(this)));
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} else {
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CancelOnMessageLoopThread();
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}
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}
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void FilePathWatcherImpl::CancelOnMessageLoopThread() {
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set_cancelled();
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if (handle_ != INVALID_HANDLE_VALUE)
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DestroyWatch();
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if (!callback_.is_null()) {
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MessageLoop::current()->RemoveDestructionObserver(this);
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callback_.Reset();
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}
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}
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void FilePathWatcherImpl::WillDestroyCurrentMessageLoop() {
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CancelOnMessageLoopThread();
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}
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void FilePathWatcherImpl::OnObjectSignaled(HANDLE object) {
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DCHECK(object == handle_);
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// Make sure we stay alive through the body of this function.
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scoped_refptr<FilePathWatcherImpl> keep_alive(this);
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if (!UpdateWatch()) {
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callback_.Run(target_, true /* error */);
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return;
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}
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// Check whether the event applies to |target_| and notify the callback.
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base::PlatformFileInfo file_info;
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bool file_exists = file_util::GetFileInfo(target_, &file_info);
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if (file_exists && (last_modified_.is_null() ||
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last_modified_ != file_info.last_modified)) {
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last_modified_ = file_info.last_modified;
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first_notification_ = base::Time::Now();
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callback_.Run(target_, false);
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} else if (file_exists && !first_notification_.is_null()) {
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// The target's last modification time is equal to what's on record. This
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// means that either an unrelated event occurred, or the target changed
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// again (file modification times only have a resolution of 1s). Comparing
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// file modification times against the wall clock is not reliable to find
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// out whether the change is recent, since this code might just run too
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// late. Moreover, there's no guarantee that file modification time and wall
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// clock times come from the same source.
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//
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// Instead, the time at which the first notification carrying the current
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// |last_notified_| time stamp is recorded. Later notifications that find
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// the same file modification time only need to be forwarded until wall
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// clock has advanced one second from the initial notification. After that
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// interval, client code is guaranteed to having seen the current revision
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// of the file.
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if (base::Time::Now() - first_notification_ >
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base::TimeDelta::FromSeconds(1)) {
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// Stop further notifications for this |last_modification_| time stamp.
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first_notification_ = base::Time();
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}
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callback_.Run(target_, false);
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} else if (!file_exists && !last_modified_.is_null()) {
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last_modified_ = base::Time();
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callback_.Run(target_, false);
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}
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// The watch may have been cancelled by the callback.
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if (handle_ != INVALID_HANDLE_VALUE)
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watcher_.StartWatching(handle_, this);
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}
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// static
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bool FilePathWatcherImpl::SetupWatchHandle(const FilePath& dir,
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bool recursive,
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HANDLE* handle) {
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*handle = FindFirstChangeNotification(
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dir.value().c_str(),
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recursive,
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FILE_NOTIFY_CHANGE_FILE_NAME | FILE_NOTIFY_CHANGE_SIZE |
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FILE_NOTIFY_CHANGE_LAST_WRITE | FILE_NOTIFY_CHANGE_DIR_NAME |
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FILE_NOTIFY_CHANGE_ATTRIBUTES | FILE_NOTIFY_CHANGE_SECURITY);
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if (*handle != INVALID_HANDLE_VALUE) {
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// Make sure the handle we got points to an existing directory. It seems
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// that windows sometimes hands out watches to directories that are
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// about to go away, but doesn't sent notifications if that happens.
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if (!DirectoryExists(dir)) {
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FindCloseChangeNotification(*handle);
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*handle = INVALID_HANDLE_VALUE;
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}
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return true;
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}
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// If FindFirstChangeNotification failed because the target directory
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// doesn't exist, access is denied (happens if the file is already gone but
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// there are still handles open), or the target is not a directory, try the
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// immediate parent directory instead.
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DWORD error_code = GetLastError();
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if (error_code != ERROR_FILE_NOT_FOUND &&
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error_code != ERROR_PATH_NOT_FOUND &&
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error_code != ERROR_ACCESS_DENIED &&
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error_code != ERROR_SHARING_VIOLATION &&
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error_code != ERROR_DIRECTORY) {
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using ::operator<<; // Pick the right operator<< below.
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DPLOG(ERROR) << "FindFirstChangeNotification failed for "
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<< dir.value();
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return false;
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}
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return true;
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}
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bool FilePathWatcherImpl::UpdateWatch() {
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if (handle_ != INVALID_HANDLE_VALUE)
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DestroyWatch();
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base::PlatformFileInfo file_info;
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if (file_util::GetFileInfo(target_, &file_info)) {
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last_modified_ = file_info.last_modified;
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first_notification_ = base::Time::Now();
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}
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// Start at the target and walk up the directory chain until we succesfully
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// create a watch handle in |handle_|. |child_dirs| keeps a stack of child
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// directories stripped from target, in reverse order.
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std::vector<FilePath> child_dirs;
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FilePath watched_path(target_);
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while (true) {
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if (!SetupWatchHandle(watched_path, recursive_watch_, &handle_))
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return false;
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// Break if a valid handle is returned. Try the parent directory otherwise.
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if (handle_ != INVALID_HANDLE_VALUE)
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break;
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// Abort if we hit the root directory.
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child_dirs.push_back(watched_path.BaseName());
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FilePath parent(watched_path.DirName());
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if (parent == watched_path) {
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DLOG(ERROR) << "Reached the root directory";
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return false;
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}
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watched_path = parent;
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}
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// At this point, handle_ is valid. However, the bottom-up search that the
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// above code performs races against directory creation. So try to walk back
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// down and see whether any children appeared in the mean time.
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while (!child_dirs.empty()) {
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watched_path = watched_path.Append(child_dirs.back());
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child_dirs.pop_back();
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HANDLE temp_handle = INVALID_HANDLE_VALUE;
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if (!SetupWatchHandle(watched_path, recursive_watch_, &temp_handle))
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return false;
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if (temp_handle == INVALID_HANDLE_VALUE)
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break;
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FindCloseChangeNotification(handle_);
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handle_ = temp_handle;
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}
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return true;
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}
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void FilePathWatcherImpl::DestroyWatch() {
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watcher_.StopWatching();
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FindCloseChangeNotification(handle_);
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handle_ = INVALID_HANDLE_VALUE;
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}
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} // namespace
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FilePathWatcher::FilePathWatcher() {
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impl_ = new FilePathWatcherImpl();
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}
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} // namespace base
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