Implement Worker-MainThread bridge for FileSystem API in Chrome

content/child/fileapi/file_system_dispatcher.cc

Index: content/child/fileapi/file_system_dispatcher.cc
diff --git a/content/child/fileapi/file_system_dispatcher.cc b/content/child/fileapi/file_system_dispatcher.cc
index 5c7d7c94e1807b89fc0a13622e1d32e0e326816e..87dfb00d6c4e17e41de924bd2c3ed1de51e4d7bb 100644
--- a/content/child/fileapi/file_system_dispatcher.cc
+++ b/content/child/fileapi/file_system_dispatcher.cc
@@ -6,12 +6,32 @@
 
 #include "base/callback.h"
 #include "base/file_util.h"
+#include "base/message_loop/message_loop_proxy.h"
 #include "base/process.h"
 #include "content/child/child_thread.h"
 #include "content/common/fileapi/file_system_messages.h"
 
 namespace content {
 
+namespace {
+
+void DidReceiveSnapshotFile(
+    int request_id,
+    base::MessageLoopProxy* message_loop) {

[michaeln, 2013/07/24 00:54:08]

You might be able to use the ThreadSafeSender here instead of manually
loop->PostTask'ing in this function.

[kinuko, 2013/07/24 09:29:09]

Done.

+  if (!message_loop->RunsTasksOnCurrentThread()) {
+    message_loop->PostTask(FROM_HERE,
+                           base::Bind(&DidReceiveSnapshotFile, request_id,
+                                      make_scoped_refptr(message_loop)));
+    return;
+  }
+  if (ChildThread::current()) {
+    ChildThread::current()->Send(
+        new FileSystemHostMsg_DidReceiveSnapshotFile(request_id));
+  }
+}
+
+}  // namespace
+
 class FileSystemDispatcher::CallbackDispatcher {
  public:
   typedef CallbackDispatcher self;
@@ -88,8 +108,9 @@ class FileSystemDispatcher::CallbackDispatcher {
 
   void DidCreateSnapshotFile(
       const base::PlatformFileInfo& file_info,
-      const base::FilePath& platform_path) {
-    snapshot_callback_.Run(file_info, platform_path);
+      const base::FilePath& platform_path,
+      const base::Closure& did_receive_snapshot) {
+    snapshot_callback_.Run(file_info, platform_path, did_receive_snapshot);

[michaeln, 2013/07/24 01:38:58]

What method/function is snapshot_callback_ this wired to? I see,
CallbacksWrapper::DidCreateSnapshotFile.

Alternatively, instead of passing a did_receive_snapshot Closure to be invoked
by that method, maybe alter that method to directly call...
  sender->Send(new FileSystemHostMsg_DidReceiveSnapshotFile(request_id));
...i guess you'd also have to pass in the request_id to that method in place of
this closure.

The closure indirection is harder to follow fwiw.

[kinuko, 2013/07/24 09:29:09]

I thought returning a closure is clearer about what is expected, but it might be
also true that adding more indirection makes things harder to follow... ok,
done.

   }
 
   void DidReadDirectory(
@@ -363,10 +384,11 @@ void FileSystemDispatcher::OnDidCreateSnapshotFile(
     const base::FilePath& platform_path) {
   CallbackDispatcher* dispatcher = dispatchers_.Lookup(request_id);
   DCHECK(dispatcher);
-  dispatcher->DidCreateSnapshotFile(file_info, platform_path);
+  dispatcher->DidCreateSnapshotFile(
+      file_info, platform_path,
+      base::Bind(&DidReceiveSnapshotFile, request_id,
+                 base::MessageLoopProxy::current()));
   dispatchers_.Remove(request_id);
-  ChildThread::current()->Send(
-      new FileSystemHostMsg_DidReceiveSnapshotFile(request_id));
 }
 
 void FileSystemDispatcher::OnDidReadDirectory(