With the batch of commits I did this weekend, the Event MPM in the async-dev Subversion branch now does write completion in a nonblocking manner. Once an entire response has been generated and passed to the output filter chain, the MPM's poller/listener thread watches the connection for writability events. When the connection becomes writable, the poller thread sends it to one of the worker threads, which writes some more output.
At this point, the event-handling code is ready for testing and review by other developers. The main changes on the async-dev branch (compared to the 2.3-dev trunk) are: 1. ap_core_output_filter: rewrite to do nonblocking writes whenever possible. 2. core, http module, and mod_logio: removed the generation of flush buckets where possible. 3. request cleanup and logging: the logger phase and subsequent destruction of the request's pool are now triggered by the destruction of an End-Of-Request bucket in the core output filter. 4. event MPM: asynchronous handling of CONN_STATE_WRITE_COMPLETION. There are several more things that need to be fixed in order to make the asynchronous write completion useful in a production release of httpd-2.x: - The main pollset in the Event MPM currently is sized to hold up to one socket descriptor per worker thread. With asynchronous keepalives and write completion, the pollset should accommodate many descriptors per thread. - The logic for starting more child processes, which Event inherited from Worker, is based on assumptions about the number of concurrent connections being equal to the number of threads. These assumptions aren't valid for a multiple-connections-per-thread MPM. - Similarly, there may be some changes needed in the flow control logic that the listener thread uses to decide whether it can do an accept. - The scoreboard probably needs a redesign. - It may be valuable to have a separate thread pool to run handlers that do arbitrarily lengthy processing, such as mod_perl and mod_php. Brian
