[Media Galleries] Filesystem interface for Mac PTP/MTP devices using ImageCaptureCore (part 3)

webkit/fileapi/media/mtp_device_delegate.h

 // 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.
 
 #ifndef WEBKIT_FILEAPI_MEDIA_MTP_DEVICE_DELEGATE_H_
 #define WEBKIT_FILEAPI_MEDIA_MTP_DEVICE_DELEGATE_H_
 
 #include "base/memory/scoped_ptr.h"
 #include "base/platform_file.h"
 #include "webkit/fileapi/file_system_file_util.h"
@@ skipping 13 matching lines @@
 class MTPDeviceDelegate {
  public:
   // Returns information about the given file path.
   virtual base::PlatformFileError GetFileInfo(
       const base::FilePath& file_path,
       base::PlatformFileInfo* file_info) = 0;
 
   // Returns a pointer to a new instance of AbstractFileEnumerator to enumerate
   // the file entries of |root| path. The instance needs to be freed by the
   // caller, and its lifetime should not extend past when the current call
-  // returns to the main media task runner thread.
+  // returns to the main media task runner thread. Callers must ensure the
+  // lifetime of the enumerator is shorter than the MTPDeviceDelegate
+  // implementation itself. Calls to the enumerator are made in the context of
+  // a SeuqencedWorkerPool, and the enumerator may block while it is being
+  // called.
   virtual scoped_ptr<FileSystemFileUtil::AbstractFileEnumerator>
       CreateFileEnumerator(const base::FilePath& root,
                            bool recursive) = 0;
 
   // Updates the temporary snapshot file contents given by |local_path| with
   // media file contents given by |device_file_path| and also returns the
-  // metadata of the temporary file.
+  // metadata of the temporary file. All calls to this interface method are
+  // made in the context of a SequencedWorkerPool, and so only one call will be
+  // active at once. Implementations may block this pool.
   virtual base::PlatformFileError CreateSnapshotFile(
       const base::FilePath& device_file_path,
       const base::FilePath& local_path,
       base::PlatformFileInfo* file_info) = 0;
 
   // Called when the
   // (1) Browser application is in shutdown mode (or)
   // (2) Last extension using this MTP device is destroyed (or)
   // (3) Attached MTP device is removed (or)
   // (4) User revoked the MTP device gallery permission.
   // Ownership of |MTPDeviceDelegate| is handed off to the delegate
   // implementation class by this call. This function should take care of
   // deleting itself on the right thread. This function should cancel all the
   // pending requests before posting any message to delete itself.
   // Called on the UI thread.
   virtual void CancelPendingTasksAndDeleteDelegate() = 0;
 
  protected:
   // Always destruct this object via CancelPendingTasksAndDeleteDelegate().
   virtual ~MTPDeviceDelegate() {}
 };
 
 }  // namespace fileapi
 
 #endif  // WEBKIT_FILEAPI_MEDIA_MTP_DEVICE_DELEGATE_H_