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

chrome/browser/media_gallery/mac/mtp_device_delegate_impl_mac.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 CHROME_BROWSER_MEDIA_GALLERY_MTP_DEVICE_DELEGATE_IMPL_MAC_H_
+#define CHROME_BROWSER_MEDIA_GALLERY_MTP_DEVICE_DELEGATE_IMPL_MAC_H_
+
+#include <vector>
+
+#include "base/file_path.h"
+#include "base/hash_tables.h"
+#include "base/memory/weak_ptr.h"
+#include "base/platform_file.h"
+#include "base/sequenced_task_runner_helpers.h"
+#include "base/synchronization/lock.h"
+#include "base/synchronization/waitable_event.h"
+#include "webkit/fileapi/file_system_file_util.h"
+#include "webkit/fileapi/media/mtp_device_delegate.h"
+
+namespace base {
+class SequencedTaskRunner;
+}
+
+namespace chrome {
+
+// Delegate for presenting an Image Capture device through the filesystem
+// API. The synthetic filesystem will be rooted at the constructed location,
+// and names of all files notified through the ItemAdded call will be
+// all appear as children of that directory. (ItemAdded calls with directories
+// will be ignored.)
+class MTPDeviceDelegateImplMac : public fileapi::MTPDeviceDelegate {
+ public:
+  MTPDeviceDelegateImplMac(const std::string& device_id,
+                           const FilePath::StringType& synthetic_path,
+                           base::SequencedTaskRunner* media_task_runner);
+
+  // MTPDeviceDelegate:
+  virtual base::PlatformFileError GetFileInfo(
+      const FilePath& file_path,
+      base::PlatformFileInfo* file_info) OVERRIDE;
+  virtual scoped_ptr<fileapi::FileSystemFileUtil::AbstractFileEnumerator>
+      CreateFileEnumerator(const FilePath& root, bool recursive) OVERRIDE;
+  virtual base::PlatformFileError CreateSnapshotFile(
+      const FilePath& device_file_path,
+      const FilePath& local_path,
+      base::PlatformFileInfo* file_info) OVERRIDE;
+  virtual void CancelPendingTasksAndDeleteDelegate() OVERRIDE;
+
+  // Forward delegates for ImageCaptureDeviceListener
+  virtual void ItemAdded(const std::string& name,
+                         const base::PlatformFileInfo& info);
+  virtual void NoMoreItems();
+  virtual void DownloadedFile(const std::string& name,
+                              base::PlatformFileError error);
+
+  // Implementation returned by |CreateFileEnumerator()|. Must be deleted
+  // before CancelPendingTasksAndDeleteDelegate is called.

[Lei Zhang, 2013/01/17 07:56:23]

What you really want is for the Enumerator to stop working and stop accessing
|delegate_| after CancelPendingTasksAndDeleteDelegate() gets called, right? 

How about when the Enumerator reaches the end, whether artificially or not, it
can set |delegate_| to NULL and be done with it?

[Greg Billock, 2013/01/25 18:41:40]

I could put another interlock between them to relax this, but I think this
contract is cheaper (since it is honored right now). I'd have to add guards in
the iterator methods, as well as the additional setters, and make sure those are
all synchronized correctly.

But in general, the interlock is complicated since the threading model is that a
caller can be blocked in the enumerator, the delegate needs to be able to know
when it can (and must) wake up the enumerator.

The async API ought to be serializable and much easier to deal with.

+  class Enumerator :
+      public fileapi::FileSystemFileUtil::AbstractFileEnumerator {
+   public:
+    explicit Enumerator(MTPDeviceDelegateImplMac* delegate);
+    virtual ~Enumerator();
+
+    virtual FilePath Next() OVERRIDE;
+    virtual int64 Size() OVERRIDE;
+    virtual base::Time LastModifiedTime() OVERRIDE;
+    virtual bool IsDirectory() OVERRIDE;
+
+    // Called by the delegate to signal any waiters that the received items
+    // list has changed state.
+    void ItemsChanged();
+
+   private:
+    MTPDeviceDelegateImplMac* delegate_;
+    size_t position_;
+    base::WaitableEvent wait_for_items_;
+  };
+
+  // GetFile and HasAllFiles called by enumerators.
+  FilePath GetFile(size_t index);
+  bool ReceivedAllFiles();
+  void RemoveEnumerator(Enumerator* enumerator);
+
+ private:
+  friend class base::DeleteHelper<MTPDeviceDelegateImplMac>;
+
+  class DeviceListener;
+
+  virtual ~MTPDeviceDelegateImplMac();
+
+  std::string device_id_;
+  FilePath root_path_;
+
+  // Stores a reference to worker pool thread. All requests and response of file
+  // operations are posted on |media_task_runner_|. All callbacks from the
+  // camera will come through this task runner as well.
+  scoped_refptr<base::SequencedTaskRunner> media_task_runner_;
+
+  // Interface object for the camera underlying this MTP session.
+  scoped_ptr<DeviceListener> camera_interface_;
+
+  // This lock protects all subsequent state. While calling into the delegate
+  // from the FileSystem API happens in sequence, these calls may be
+  // interleaved with calls on other threads in the sequenced task runner
+  // forwarded from the device.
+  base::Lock mutex_;
+
+  // Weak pointer to the enumerator which may be listening for files to come in.
+  Enumerator* enumerator_;
+
+  // Stores a map from filename to file metadata received from the camera.
+  base::hash_map<FilePath::StringType, base::PlatformFileInfo> file_info_;
+
+  // Notification for pending download.
+  base::WaitableEvent* file_download_event_;
+
+  // Resulting error code for pending download.
+  base::PlatformFileError file_download_error_;
+
+  // List of files received from the camera.
+  std::vector<FilePath> file_paths_;
+
+  // Set to true when all file metadata has been received from the camera.
+  bool received_all_files_;
+
+  DISALLOW_COPY_AND_ASSIGN(MTPDeviceDelegateImplMac);
+};
+
+}  // namespace chrome
+
+#endif  // CHROME_BROWSER_MEDIA_GALLERY_MTP_DEVICE_DELEGATE_IMPL_MAC_H_