I just committed a change in mod_http2 that will return idle connections back to the mpm, expecting to be invoked again when new data arrives. I learned quite something about event (have not looked much at motorz yet) and am thinking about improvements. If knowledgeable people could give me a hand here, I'd highly appreciate it.
Observation 1: mapping conn_states As I understand it, the connection state model, as defined in conn_state_e, enables asynchronous processing in two states: a. CONN_STATE_CHECK_REQUEST_LINE_READABLE, check read, invoke ap_run_process_connection() on data b. CONN_STATE_WRITE_COMPLETION, check write, if data is still in out filters An invocation of ap_run_process_connection() is expected to return, usually in WRITE_COMPLETION state. Then any data is attempted to be written. When this succeeds, the next state depends on secondary flags such as c->aborted, c->keepalive and c->data_in_input_filters. HTTP/2 processing has one state where it fits into this model: when no more streams are open. This is what is currently implemented in trunk. However, there is another state in HTTP/2 processing, where a BLOCK_READ is performed: flow control on streaming out responses. Basically, the client has a window of n bytes, the server sends n response bytes and then needs to wait for the client to increase the window again. This would be a good time to resume processing back to the mpm, and initially I did so. But that breaks under load. Under load, the event mpm feels free to close connections in certain states - I think CONN_STATE_CHECK_REQUEST_LINE_READABLE. That is fine for a HTTP/1 connection as it always is between requests here. But HTTP/2 would also like to use read events, but unloading a child by closing such connections is not the right thing to do. Is there a way mod_http2 can achieve this or do we need another flag in conn_rec/cs? Observation 2: controlled close HTTP/2 would like to send out a last frame when closing a connection in a controlled/timeout way. Do we need another hook for that? Something like "pre_close_connection"? Observation 3: timeouts a. If admins would like to have another Timeout for HTTP/2 connections, they are currently stuck with configuring one Timeout which goes to server_rec->timeout, right? For idle connections, clients already try to keep it open longer. It would be nice to give admins a choice here for different values based on the selected protocol. How to best do this? b. Handling own timeouts: if I want, during processing the connection, a different socket timeout, I can just set it using apr_socket_timeout_set()? Shall I restore it back to server->timeout before returning? c. What would be the best way to wait for a file description *and* conditional event simultaneously? mod_http2 has now a sort of pool loop with double backup timer for situations where it needs to watch both client and backend processes. Cheers, Stefan
