Use associated interface on DownloadedTempFile

content/browser/loader/downloaded_temp_file_impl.cc

 // Copyright 2016 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/browser/loader/downloaded_temp_file_impl.h"
 
 #include "content/browser/loader/resource_dispatcher_host_impl.h"
+#include "mojo/public/cpp/bindings/associated_group.h"
+#include "mojo/public/cpp/bindings/strong_associated_binding.h"
 #include "mojo/public/cpp/bindings/strong_binding.h"
 
 namespace content {
 
 // static
-mojo::InterfacePtr<mojom::DownloadedTempFile> DownloadedTempFileImpl::Create(
+mojom::DownloadedTempFileAssociatedPtrInfo DownloadedTempFileImpl::Create(
+    mojo::AssociatedGroup* associated_group,
+    int child_id,
+    int request_id) {
+  mojo::AssociatedInterfacePtrInfo<mojom::DownloadedTempFile> ptr_info;
+  mojo::AssociatedInterfaceRequest<mojom::DownloadedTempFile> request;

[mmenke, 2016/12/13 20:24:06]

Are there any docs on what an associated interface is?  All mojo class-level
docs I see assume you already know that.

[dcheng, 2016/12/13 22:37:44]

I guess we should clarify the docs.

Basically, with Mojo, the default is each interface you connect to has its own
message pipe. Since there is no ordering guarantee between two message pipes,
that means it's possible for messages on different pipes to race.

With IPC:
  sender->Send(new FooMsg(...));
  sender->Send(new BarMsg(...));

is well-ordered: it's guaranteed the receiver will process FooMsg before BarMsg.

However, with Mojo:
  foo->This(...);
  bar->That(...);

Either ordering is possible: the IPCs are sent on different message pipes, and
there's no guarantee which one will be handled first by the receiver.

Associated interfaces are designed to solve this problem by allowing multiple
mojo interface instances to share a single message pipe. If |foo| and |bar| are
associated interfaces, then it's guaranteed that This(...) will be handled
before That(...).

+  associated_group->CreateAssociatedInterface(
+      mojo::AssociatedGroup::WILL_PASS_PTR, &ptr_info, &request);
+  mojo::MakeStrongAssociatedBinding(
+      base::MakeUnique<DownloadedTempFileImpl>(child_id, request_id),
+      std::move(request));
+  return ptr_info;
+}
+
+// static
+mojom::DownloadedTempFilePtr DownloadedTempFileImpl::CreateForTesting(
     int child_id,
     int request_id) {
   mojo::InterfacePtr<mojom::DownloadedTempFile> ptr;
-  auto binding = mojo::MakeStrongBinding(
+  mojo::MakeStrongBinding(
       base::MakeUnique<DownloadedTempFileImpl>(child_id, request_id),
       mojo::GetProxy(&ptr));
   return ptr;
 }
 
 DownloadedTempFileImpl::~DownloadedTempFileImpl() {
   ResourceDispatcherHostImpl::Get()->UnregisterDownloadedTempFile(child_id_,
                                                                   request_id_);
 }
 DownloadedTempFileImpl::DownloadedTempFileImpl(int child_id, int request_id)
     : child_id_(child_id), request_id_(request_id) {}
 
 }  // namespace content