base/files/file_path_watcher.h

   1 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 // This module provides a way to monitor a file or directory for changes.
   6
   7 #ifndef BASE_FILES_FILE_PATH_WATCHER_H_
   8 #define BASE_FILES_FILE_PATH_WATCHER_H_
   9 #pragma once
  10
  11 #include "base/base_export.h"
  12 #include "base/basictypes.h"
  13 #include "base/file_path.h"
  14 #include "base/memory/ref_counted.h"
  15 #include "base/message_loop_proxy.h"
  16
  17 namespace base {
  18 namespace files {
  19
  20 // This class lets you register interest in changes on a FilePath.
  21 // The delegate will get called whenever the file or directory referenced by the
  22 // FilePath is changed, including created or deleted. Due to limitations in the
  23 // underlying OS APIs, FilePathWatcher has slightly different semantics on OS X
  24 // than on Windows or Linux. FilePathWatcher on Linux and Windows will detect
  25 // modifications to files in a watched directory. FilePathWatcher on Mac will
  26 // detect the creation and deletion of files in a watched directory, but will
  27 // not detect modifications to those files. See file_path_watcher_mac.cc for
  28 // details.
  29 class BASE_EXPORT FilePathWatcher {
  30  public:
  31   // Declares the callback client code implements to receive notifications. Note
  32   // that implementations of this interface should not keep a reference to the
  33   // corresponding FileWatcher object to prevent a reference cycle.
  34   class Delegate : public base::RefCountedThreadSafe<Delegate> {
  35    public:
  36     virtual ~Delegate() {}
  37     virtual void OnFilePathChanged(const FilePath& path) = 0;
  38     // Called when platform specific code detected an error. The watcher will
  39     // not call OnFilePathChanged for future changes.
  40     virtual void OnFilePathError(const FilePath& path) {}
  41   };
  42
  43   // Used internally to encapsulate different members on different platforms.
  44   // TODO(jhawkins): Move this into its own file. Also fix the confusing naming
  45   // wrt Delegate vs PlatformDelegate.
  46   class PlatformDelegate : public base::RefCountedThreadSafe<PlatformDelegate> {
  47    public:
  48     PlatformDelegate();
  49
  50     // Start watching for the given |path| and notify |delegate| about changes.
  51     virtual bool Watch(const FilePath& path,
  52                        Delegate* delegate) WARN_UNUSED_RESULT = 0;
  53
  54     // Stop watching. This is called from FilePathWatcher's dtor in order to
  55     // allow to shut down properly while the object is still alive.
  56     // It can be called from any thread.
  57     virtual void Cancel() = 0;
  58
  59    protected:
  60     friend class FilePathWatcher;
  61
  62     virtual ~PlatformDelegate();
  63
  64     // Stop watching. This is only called on the thread of the appropriate
  65     // message loop. Since it can also be called more than once, it should
  66     // check |is_cancelled()| to avoid duplicate work.
  67     virtual void CancelOnMessageLoopThread() = 0;
  68
  69     scoped_refptr<base::MessageLoopProxy> message_loop() const {
  70       return message_loop_;
  71     }
  72
  73     void set_message_loop(base::MessageLoopProxy* loop) {
  74       message_loop_ = loop;
  75     }
  76
  77     // Must be called before the PlatformDelegate is deleted.
  78     void set_cancelled() {
  79       cancelled_ = true;
  80     }
  81
  82     bool is_cancelled() const {
  83       return cancelled_;
  84     }
  85
  86    private:
  87     friend class base::RefCountedThreadSafe<PlatformDelegate>;
  88
  89     scoped_refptr<base::MessageLoopProxy> message_loop_;
  90     bool cancelled_;
  91   };
  92
  93   FilePathWatcher();
  94   ~FilePathWatcher();
  95
  96   // A callback that always cleans up the PlatformDelegate, either when executed
  97   // or when deleted without having been executed at all, as can happen during
  98   // shutdown.
  99   static void CancelWatch(const scoped_refptr<PlatformDelegate>& delegate);
 100
 101   // Register interest in any changes on |path|. OnPathChanged will be called
 102   // back for each change. Returns true on success.
 103   // OnFilePathChanged() will be called on the same thread as Watch() is called,
 104   // which should have a MessageLoop of TYPE_IO.
 105   bool Watch(const FilePath& path, Delegate* delegate) WARN_UNUSED_RESULT;
 106
 107  private:
 108   scoped_refptr<PlatformDelegate> impl_;
 109
 110   DISALLOW_COPY_AND_ASSIGN(FilePathWatcher);
 111 };
 112
 113 }  // namespace files
 114 }  // namespace base
 115
 116 #endif  // BASE_FILES_FILE_PATH_WATCHER_H_