id,summary,reporter,owner,description,type,status,milestone,component,version,severity,resolution,keywords,cc
8967,Spurious zero bytes written and eof notifications highlight ASIO IOCP issues,simoncperkins@…,chris_kohlhoff,"I have been working on a multi-threaded boost asio based HTTP client. My tests perform hundreds of HTTP calls against a variety of web servers.

The tests run reliably on OS X and on Windows with the BOOST_ASIO_DISABLE_IOCP flag set. I use multiple threads calling io_service:run().

However, on Windows using IOCP I was seeing occasional notifications that zero bytes had been written with async_write even though data had successfully been written to the socket and was received by the web server.

I also saw random boost::asio::error::eof notications from async_read_some even though there was more data to read and the tcp socket's available() method returned a non-zero value.

In trying to track down the problem I reviewed the implementation of the ASIO IOCP implementation and found several issues:

 1) WSARecv and WSASend were supplying non-NULL for the lpNumberOfBytesRecvd parameter with an overlapped socket. The MSDN docs say ""Use NULL for this parameter if the lpOverlapped parameter is not NULL to avoid potentially erroneous results. This parameter can be NULL only if the lpOverlapped parameter is not NULL.

 2) PostQueuedCompletionStatus is only needed to deliver errors where WSARecv and WSASend synchronously fail. Instead it was always being used for successful synchronous and pending I/O through win_iocp_io_service::on_pending. This is not required because an overlapped socket's results are automatically delivered to thread(s) calling GetQueuedCompletionStatus. I believe this could lead to incorrect behaviour due to the explicit and implicit posting of each I/O request. Also, this would increase the number of notifications that the IOCP would have to handle.

 3) The ready_ flag seems to be unnecessary for a correct implementation and could cause notifications from QueuedCompletionStatus to be ignored  

I have attached a patch file of my changes with comments prefixed with SP: indicating the reason for each of the changes.

After applying these changes to Boost ASIO in 1.54 I can now reliably run the IOCP version of the tests on Windows 7.

I believe the modified implementation is closer to that expected when using sockets and I/O completion ports.",Bugs,closed,To Be Determined,asio,Boost 1.54.0,Problem,invalid,eof GetQueuedCompletionStatus WSARecv WSASend overlapped,