Redesigned and refactored ScopedMTPDeviceMapEntry, MTPDeviceMapService & MTPDeviceDelegate classes.

webkit/fileapi/file_system_operation_context.h

Index: webkit/fileapi/file_system_operation_context.h
diff --git a/webkit/fileapi/file_system_operation_context.h b/webkit/fileapi/file_system_operation_context.h
index 067e0d8886b81dd64345fd19e3767233c92b8e7e..aaf2b4e5c812fb48f9745ffc2110709feedf1d87 100644
--- a/webkit/fileapi/file_system_operation_context.h
+++ b/webkit/fileapi/file_system_operation_context.h
@@ -6,6 +6,7 @@
 #define WEBKIT_FILEAPI_FILE_SYSTEM_OPERATION_CONTEXT_H_
 
 #include "base/memory/ref_counted.h"
+#include "base/memory/weak_ptr.h"
 #include "webkit/fileapi/file_system_context.h"
 #include "webkit/fileapi/media/mtp_device_file_system_config.h"
 #include "webkit/fileapi/task_runner_bound_observer_list.h"
@@ -39,11 +40,11 @@ class WEBKIT_STORAGE_EXPORT_PRIVATE FileSystemOperationContext {
 
 #if defined(SUPPORT_MTP_DEVICE_FILESYSTEM)
   void set_mtp_device_delegate(MTPDeviceDelegate* delegate) {
-    mtp_device_delegate_ = delegate;
+    mtp_device_delegate_ = delegate->GetAsWeakPtrOnIOThread();
   }
 
-  MTPDeviceDelegate* mtp_device_delegate() const {
-    return mtp_device_delegate_.get();
+  base::WeakPtr<MTPDeviceDelegate> mtp_device_delegate() const {

[kinuko, 2012/11/15 10:23:39]

I'm afraid this weakptr is created on IO thread but may be accessed on FILE
thread.

[kmadhusu, 2012/11/15 17:52:24]

Can you please provide more details on how this can be accessed on FILE thread?

When I tested the code, I didn't not hit any invalid thread access error.
WeakPtr thread checker seems to be happy. As you said, I create the WeakPtr
@line 43. "delegate->GetAsWeakPtrOnIOThread()" detaches the weak pointer from IO
thread. I thought we dereference this weak pointer only in
device_media_file_util which is called on media sequenced task runner thread. 

+    return mtp_device_delegate_;
   }
 #endif
 
@@ -92,7 +93,7 @@ class WEBKIT_STORAGE_EXPORT_PRIVATE FileSystemOperationContext {
 
 #if defined(SUPPORT_MTP_DEVICE_FILESYSTEM)
   // Store the current mtp device delegate.
-  scoped_refptr<MTPDeviceDelegate> mtp_device_delegate_;
+  base::WeakPtr<MTPDeviceDelegate> mtp_device_delegate_;
 #endif
 };