Implement Worker-MainThread bridge for FileWriter in Chrome

content/child/fileapi/webfilewriter_impl.cc

 // Copyright 2013 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.
 
 #include "content/child/fileapi/webfilewriter_impl.h"
 
 #include "base/bind.h"
+#include "base/platform_file.h"
 #include "content/child/child_thread.h"
 #include "content/child/fileapi/file_system_dispatcher.h"
+#include "webkit/child/worker_task_runner.h"
+
+using webkit_glue::WorkerTaskRunner;
 
 namespace content {
 
 namespace {
 
-inline FileSystemDispatcher* GetFileSystemDispatcher() {
-  return ChildThread::current()->file_system_dispatcher();
+FileSystemDispatcher* GetFileSystemDispatcher() {
+  return ChildThread::current() ?
+      ChildThread::current()->file_system_dispatcher() : NULL;
 }
 
 }  // namespace
 
+typedef FileSystemDispatcher::StatusCallback StatusCallback;
+typedef FileSystemDispatcher::WriteCallback WriteCallback;
+
+// This instance may be created outside main thread but runs mainly
+// on main thread.
+class WebFileWriterImpl::WriterBridge
+    : public base::RefCountedThreadSafe<WriterBridge> {
+ public:
+  WriterBridge()
+      : request_id_(0),
+        thread_id_(WorkerTaskRunner::Instance()->CurrentWorkerId()) {}
+
+  void Truncate(const GURL& path, int64 offset,
+                const StatusCallback& status_callback) {
+    status_callback_ = status_callback;
+    if (!GetFileSystemDispatcher())
+      return;
+    ChildThread::current()->file_system_dispatcher()->Truncate(
+        path, offset, &request_id_,
+        base::Bind(&WriterBridge::DidFinish, this));
+  }
+
+  void Write(const GURL& path, const GURL& blob_url, int64 offset,
+             const WriteCallback& write_callback,
+             const StatusCallback& error_callback) {
+    write_callback_ = write_callback;
+    status_callback_ = error_callback;
+    if (!GetFileSystemDispatcher())
+      return;
+    ChildThread::current()->file_system_dispatcher()->Write(
+        path, blob_url, offset, &request_id_,
+        base::Bind(&WriterBridge::DidWrite, this),
+        base::Bind(&WriterBridge::DidFinish, this));
+  }
+
+  void Cancel(const StatusCallback& status_callback) {
+    status_callback_ = status_callback;
+    if (!GetFileSystemDispatcher())
+      return;
+    ChildThread::current()->file_system_dispatcher()->Cancel(
+        request_id_,
+        base::Bind(&WriterBridge::DidFinish, this));
+  }
+
+ private:
+  friend class base::RefCountedThreadSafe<WriterBridge>;
+  virtual ~WriterBridge() {}
+
+  void DidWrite(int64 bytes, bool complete) {
+    PostTaskToWorker(base::Bind(write_callback_, bytes, complete));
+  }
+
+  void DidFinish(base::PlatformFileError status) {
+    PostTaskToWorker(base::Bind(status_callback_, status));
+  }
+
+  void PostTaskToWorker(const base::Closure& closure) {
+    if (!thread_id_)
+      closure.Run();
+    else
+      WorkerTaskRunner::Instance()->PostTask(thread_id_, closure);
+  }
+
+  StatusCallback status_callback_;
+  WriteCallback write_callback_;
+  int request_id_;
+  int thread_id_;
+};
+
 WebFileWriterImpl::WebFileWriterImpl(
-     const GURL& path, WebKit::WebFileWriterClient* client)
+     const GURL& path, WebKit::WebFileWriterClient* client,
+     base::MessageLoopProxy* main_thread_loop)
   : WebFileWriterBase(path, client),
-    request_id_(0) {
+    main_thread_loop_(main_thread_loop),
+    bridge_(new WriterBridge) {
 }
 
 WebFileWriterImpl::~WebFileWriterImpl() {
 }
 
 void WebFileWriterImpl::DoTruncate(const GURL& path, int64 offset) {
-  // The FileSystemDispatcher takes ownership of the CallbackDispatcher.
-  GetFileSystemDispatcher()->Truncate(
-      path, offset, &request_id_,
-      base::Bind(&WebFileWriterImpl::DidFinish, AsWeakPtr()));
+  RunOnMainThread(base::Bind(&WriterBridge::Truncate, bridge_,
+      path, offset,
+      base::Bind(&WebFileWriterImpl::DidFinish, AsWeakPtr())));
 }
 
 void WebFileWriterImpl::DoWrite(
     const GURL& path, const GURL& blob_url, int64 offset) {
-  GetFileSystemDispatcher()->Write(
-      path, blob_url, offset, &request_id_,
+  RunOnMainThread(base::Bind(&WriterBridge::Write, bridge_,
+      path, blob_url, offset,
       base::Bind(&WebFileWriterImpl::DidWrite, AsWeakPtr()),
-      base::Bind(&WebFileWriterImpl::DidFinish, AsWeakPtr()));
+      base::Bind(&WebFileWriterImpl::DidFinish, AsWeakPtr())));
 }
 
 void WebFileWriterImpl::DoCancel() {
-  GetFileSystemDispatcher()->Cancel(
-      request_id_,
-      base::Bind(&WebFileWriterImpl::DidFinish, AsWeakPtr()));
+  RunOnMainThread(base::Bind(&WriterBridge::Cancel, bridge_,
+      base::Bind(&WebFileWriterImpl::DidFinish, AsWeakPtr())));
+}
+
+void WebFileWriterImpl::RunOnMainThread(const base::Closure& closure) {
+  if (main_thread_loop_->RunsTasksOnCurrentThread())
+    closure.Run();
+  else
+    main_thread_loop_->PostTask(FROM_HERE, closure);
 }
 
 }  // namespace content