Debugging the renderer process

#1

Hi all,

I’m working on an Atom-Shell-based WebRTC video chat application. It’s running nicely on Mac OS, but on Windows it occasionally fails such that the render process (i.e. “atom.exe --type=renderer …”) exits suddenly, leaving a blank white window behind which is unresponsive to mouse or keyboard input. The other atom.exe processes continue running, and the user must close the app via the task bar icon. This seems to follow immediately upon receiving a WebRTC SDP offer or answer from a remote peer, but so far I haven’t been able to narrow it down further than that. Running it from the Visual Studio debugger shows that it’s not crashing (i.e. no access violations); just exiting for no apparent reason.

Any ideas what would explain this behavior? Is it something that could plausibly be caused by a bug in the application’s JavaScript, or should I focus on the C++ code? What are my best options for debugging it?

Thanks for reading.

#2

The first thing I would do is something like:

ipc = require('ipc')
window.onerror = function(e) {
  ipc.send('unhandled-exception', e.message)
}

Then catch those in your browser and write them out to a file somewhere

#3

Thanks, Paul. I tried what you suggested, but didn’t get any output.

I’m going to study the libchromiumcontent code a bit and see if I can add logging there. I’ll post again if I learn anything useful.

#4

Update: it turns out the renderer process is crashing after all. I found http://www.chromium.org/developers/how-tos/debugging#TOC-Attaching-to-the-renderer, which taught me how to attach to the process before it got the access violation, and then got a stack trace in Visual Studio:

chromiumcontent.dll!base::Thread::message_loop_proxy() Line 150	C++
chromiumcontent.dll!content::ChildProcess::io_message_loop_proxy() Line 47	C++
chromiumcontent.dll!content::VideoCaptureImplManager::UnrefDevice(int id) Line 170	C++
chromiumcontent.dll!base::internal::Invoker<2,base::internal::BindState<base::internal::RunnableAdapter<void (__thiscall content::AppCacheResponseIO::*)(int)>,void __cdecl(content::AppCacheResponseIO *,int),void __cdecl(base::WeakPtr<content::AppCacheResponseIO>,int)>,void __cdecl(content::AppCacheResponseIO *,int)>::Run(base::internal::BindStateBase * base) Line 1253	C++
chromiumcontent.dll!content::VideoCapturerDelegate::~VideoCapturerDelegate() Line 59	C++
[External Code]	
chromiumcontent.dll!scoped_refptr<net::IOBuffer>::~scoped_refptr<net::IOBuffer>() Line 295	C++
chromiumcontent.dll!base::internal::BindState<base::internal::RunnableAdapter<void (__cdecl*)(base::TaskRunner *,base::Callback<void __cdecl(void)> const &)>,void __cdecl(base::TaskRunner *,base::Callback<void __cdecl(void)> const &),void __cdecl(scoped_refptr<base::MessageLoopProxy>,base::Callback<void __cdecl(void)>)>::~BindState<base::internal::RunnableAdapter<void (__cdecl*)(base::TaskRunner *,base::Callback<void __cdecl(void)> const &)>,void __cdecl(base::TaskRunner *,base::Callback<void __cdecl(void)> const &),void __cdecl(scoped_refptr<base::MessageLoopProxy>,base::Callback<void __cdecl(void)>)>() Line 2591	C++
[External Code]	
chromiumcontent.dll!scoped_refptr<net::IOBuffer>::~scoped_refptr<net::IOBuffer>() Line 295	C++
chromiumcontent.dll!content::VideoCaptureImpl::OnDeviceSupportedFormatsEnumerated(const std::vector<media::VideoCaptureFormat,std::allocator<media::VideoCaptureFormat> > & supported_formats) Line 358	C++
chromiumcontent.dll!content::VideoCaptureMessageFilter::OnDeviceSupportedFormatsEnumerated(int device_id, const std::vector<media::VideoCaptureFormat,std::allocator<media::VideoCaptureFormat> > & supported_formats) Line 200	C++
chromiumcontent.dll!VideoCaptureMsg_DeviceFormatsInUseReceived::Dispatch<content::VideoCaptureMessageFilter,content::VideoCaptureMessageFilter,void,void (__thiscall content::VideoCaptureMessageFilter::*)(int,std::vector<media::VideoCaptureFormat,std::allocator<media::VideoCaptureFormat> > const &)>(const IPC::Message * msg, content::VideoCaptureMessageFilter * obj, content::VideoCaptureMessageFilter * sender, void * parameter, void (int, const std::vector<media::VideoCaptureFormat,std::allocator<media::VideoCaptureFormat> > &) * func) Line 77	C++
chromiumcontent.dll!content::VideoCaptureMessageFilter::OnMessageReceived(const IPC::Message & message) Line 68	C++
chromiumcontent.dll!IPC::`anonymous namespace'::TryFiltersImpl(std::vector<IPC::MessageFilter *,std::allocator<IPC::MessageFilter *> > & filters, const IPC::Message & message) Line 18	C++
chromiumcontent.dll!IPC::MessageFilterRouter::TryFilters(const IPC::Message & message) Line 76	C++
chromiumcontent.dll!IPC::ChannelProxy::Context::TryFilters(const IPC::Message & message) Line 67	C++
chromiumcontent.dll!IPC::SyncChannel::SyncContext::OnMessageReceived(const IPC::Message & msg) Line 331	C++
chromiumcontent.dll!IPC::internal::ChannelReader::DispatchInputData(const char * input_data, int input_data_len) Line 98	C++
chromiumcontent.dll!IPC::internal::ChannelReader::AsyncReadComplete(int bytes_read) Line 39	C++
chromiumcontent.dll!IPC::ChannelWin::OnIOCompleted(base::MessagePumpForIO::IOContext * context, unsigned long bytes_transfered, unsigned long error) Line 513	C++
chromiumcontent.dll!base::MessagePumpForIO::DoRunLoop() Line 483	C++
chromiumcontent.dll!base::MessagePumpWin::RunWithDispatcher(base::MessagePump::Delegate * delegate, base::MessagePumpDispatcher * dispatcher) Line 51	C++
chromiumcontent.dll!base::MessagePumpWin::Run(base::MessagePump::Delegate * delegate) Line 34	C++
chromiumcontent.dll!base::MessageLoop::RunHandler() Line 415	C++
chromiumcontent.dll!base::RunLoop::Run() Line 55	C++
chromiumcontent.dll!base::MessageLoop::Run() Line 309	C++
chromiumcontent.dll!base::Thread::Run(base::MessageLoop * message_loop) Line 175	C++
chromiumcontent.dll!base::Thread::ThreadMain() Line 232	C++
chromiumcontent.dll!base::`anonymous namespace'::ThreadFunc(void * params) Line 80	C++
[External Code]	
[Frames below may be incorrect and/or missing, no symbols loaded for kernel32.dll]

Looks like a bug in Chromium. I’ll post a bug there.

#5

For the record, I’ve opened a bug with the Chromium project and attached a workaround patch for the issue I was seeing: https://code.google.com/p/chromium/issues/detail?id=444177

See also: https://github.com/atom/atom-shell/issues/951