chromium ipc channel on Browser process

Let's look around how to create and use Channel.
* before going on, must read http://www.chromium.org/developers/design-documents/inter-process-communication

I demonstrate how Browser process receives "OnRequestResource" request from Render process.

1. ChannelProxy and Channel creation on ui thread

- when loading url, RenderProcessHost is created.
- at that time, ChannelProxy and Channel are craeted.
- after creating Channel in ChannelProxy::Init(), post OnChannelOpened task to io thread.

context_->ipc_task_runner()->PostTask(FROM_HERE, base::Bind(&Context::OnChannelOpened, context_.get()));

FYI, RenderProcessHostImpl::Init() installs many(~30) filters into ChannelProxy via RenderProcessHostImpl::CreateMessageFilters() after creating ChannelProxy.

IPC::Channel::Channel() at ipc_channel_posix.cc:955 0x1abe7f0 
IPC::ChannelProxy::Context::CreateChannel() at ipc_channel_proxy.cc:68 0x1abfbc3 
IPC::ChannelProxy::Init() at ipc_channel_proxy.cc:329 0x1ac0d8d 
IPC::ChannelProxy::ChannelProxy() at ipc_channel_proxy.cc:294 0x1ac0a07 
content::RenderProcessHostImpl::Init() at render_process_host_impl.cc:495 0x5bd1b3 
content::RenderViewHostImpl::CreateRenderView() at render_view_host_impl.cc:236 0x5d03fb 
content::WebContentsImpl::CreateRenderViewForRenderManager() at web_contents_impl.cc:3,494 0x666e55 
content::RenderViewHostManager::InitRenderView() at render_view_host_manager.cc:663 0x89f0cc 
content::RenderViewHostManager::CreateRenderView() at render_view_host_manager.cc:639 0x89ef95 
content::RenderViewHostManager::UpdateRendererStateForNavigate() at render_view_host_manager.cc:814 0x89fc7d 
content::RenderViewHostManager::Navigate() at render_view_host_manager.cc:122 0x89d35a 
content::WebContentsImpl::NavigateToEntry() at web_contents_impl.cc:1,713 0x65f469 
content::WebContentsImpl::NavigateToPendingEntry() at web_contents_impl.cc:1,680 0x65f126 
content::NavigationControllerImpl::NavigateToPendingEntry() at navigation_controller_impl.cc:1,537 0x898edb 
content::NavigationControllerImpl::LoadEntry() at navigation_controller_impl.cc:398 0x893c0e 
content::NavigationControllerImpl::LoadURLWithParams() at navigation_controller_impl.cc:685 0x894f73 
content::Shell::LoadURLForFrame() at shell.cc:180 0x458723 
content::Shell::LoadURL() at shell.cc:172 0x45866d 
content::Shell::OnURLEntryActivate() at shell_gtk.cc:284 0x45bc41 
content::Shell::OnURLEntryActivateThunk() at shell.h:207 0x45bf12 
g_closure_invoke() at gclosure.c:777 0x7ffff7048140 

2. Channel connection established on io thread

For example, register OnLibeventNotification callback.
 - register callback on fd

event_set(evt.get(), fd, event_mask, OnLibeventNotification, controller);

 - set Watcher (ChannelImpl extends) that is stored in Closure.

controller->set_watcher(delegate);

Back trace

base::MessagePumpLibevent::WatchFileDescriptor() at message_pump_libevent.cc:186 0x925adf 
base::MessageLoopForIO::WatchFileDescriptor() at message_loop.cc:829 0x972a2a 
IPC::Channel::ChannelImpl::AcceptConnection() at ipc_channel_posix.cc:671 0x1abd265 
IPC::Channel::ChannelImpl::Connect() at ipc_channel_posix.cc:345 0x1abb2b4 
IPC::Channel::Connect() at ipc_channel_posix.cc:963 0x1abe8ea 
IPC::ChannelProxy::Context::OnChannelOpened() at ipc_channel_proxy.cc:145 0x1ac00bb 
base::internal::RunnableAdapter{void () at bind_internal.h:134 0x1ac36a1 
base::internal::InvokeHelper{false, void, base::internal::RunnableAdapter{void () at bind_internal.h:871 0x1ac32fc 
base::internal::Invoker{1, base::internal::BindState{base::internal::RunnableAdapter{void () at bind_internal.h:1,173 0x1ac2e37 
base::Callback{void () at callback.h:396 0x44840a 
base::MessageLoop::RunTask() at message_loop.cc:484 0x971c03 

3. Receive "OnRequestResource" request on io thread.

- MessagePumpLibevent::FileDescriptorWatcher::OnFileCanReadWithoutBlocking dispatches the event to Watcher(ChannelImpl)
- ChannelImpl dispatches the event to Channel::Context
- BrowserMessageFilter intercepts the event
- BrowserMessageFilter dispatches the event to ResourceMessageFilter
It is very consistent with chromium's doc: http://dev.chromium.org/developers/design-documents/multi-process-resource-loading

content::ResourceDispatcherHostImpl::OnRequestResource() at resource_dispatcher_host_impl.cc:884 0x585dcd 
ResourceHostMsg_RequestResource::Dispatch{content::ResourceDispatcherHostImpl, content::ResourceDispatcherHostImpl, int, ResourceHostMsg_Request const&}() at resource_messages.h:269 0x58efe2 
content::ResourceDispatcherHostImpl::OnMessageReceived() at resource_dispatcher_host_impl.cc:841 0x58565f 
content::ResourceMessageFilter::OnMessageReceived() at resource_message_filter.cc:49 0x5a8029 
content::BrowserMessageFilter::DispatchMessage() at browser_message_filter.cc:136 0x4daafa 
content::BrowserMessageFilter::OnMessageReceived() at browser_message_filter.cc:52 0x4da62a 
IPC::ChannelProxy::Context::TryFilters() at ipc_channel_proxy.cc:79 0x1abfc63 
IPC::ChannelProxy::Context::OnMessageReceived() at ipc_channel_proxy.cc:93 0x1abfce7 
IPC::internal::ChannelReader::DispatchInputData() at ipc_channel_reader.cc:90 0x1ac44a8 
IPC::internal::ChannelReader::ProcessIncomingMessages() at ipc_channel_reader.cc:32 0x1ac4031 
IPC::Channel::ChannelImpl::OnFileCanReadWithoutBlocking() at ipc_channel_posix.cc:641 0x1abd047 
base::MessagePumpLibevent::FileDescriptorWatcher::OnFileCanReadWithoutBlocking() at message_pump_libevent.cc:102 0x924f10 
base::MessagePumpLibevent::OnLibeventNotification() at message_pump_libevent.cc:359 0x926966 
event_process_active() at event.c:385 0x1c53385 
event_base_loop() at event.c:525 0x1c536a8 
base::MessagePumpLibevent::Run() at message_pump_libevent.cc:262 0x925ee9 
base::MessageLoop::RunInternal() at message_loop.cc:441 0x97179e 
base::MessageLoop::RunHandler() at message_loop.cc:414 0x971648 
base::RunLoop::Run() at run_loop.cc:45 0x9a2020 
base::MessageLoop::Run() at message_loop.cc:321 0x970ee6 
base::Thread::Run() at thread.cc:159 0x9d6092