Lighttpd

https://github.com/lighttpd/lighttpd1.4/pull/50 adds the ability to tune listen backlog queue size if you have measured that your FastCGI can keep up with a given number of requests in a given amount of time and want to limit the load on the backend. See discussions in #2116 and #1825.

https://github.com/lighttpd/lighttpd1.4/pull/53 improves the control flow logic in dynamic handlers, and so they will abort the connection to the backend after configured timeouts. (Note there is more work that needs to be done to add additional timeout configuration options.)

While there is an application-level FastCGI message to send to abort a FastCGI request, lighttpd does not send it. Instead, since lighttpd sends only one request on a FastCGI socket connection (instead of using the feature of multiplexing multiple requests on a FastCGI socket connection), lighttpd closes the FastCGI socket connection when lighttpd detects that a client connection has been aborted.

For a backend application to get this information, the backend FastCGI application code must be written to asynchronously listen for FastCGI messages -- including handling the closing of the FastCGI socket connection -- and then must communicate this information to the running FastCGI request handler. Please be aware that many FastCGI applications do not do this, as they are written in a simple serialized loop that accepts a request, processes it, sends the response, and then waits for the next request.

The following is a minimal patch so that lighttpd will detect if client disconnects. It removes interest in FDEVENT_READ and FDEVENT_WRITE, but will still be able to receive FDEVENT_HUP or FDEVENT_ERR. This will avoid sending the request to backend if the request has not yet been sent to the backend, and will result in closing the connection to the backend if the response has not yet been received, or is in the process of being received.

The check for (1 == fd) in fdevent_event_set() is because the connection might have been added to the joblist and connection_state_machine() might be called after the connection has been closed and con>state has been reset to CON_STATE_CONNECT.

diff --git a/src/connections.c b/src/connections.c
index f33fcd6..b316f2a 100644
--- a/src/connections.c
+++ b/src/connections.c
@@ -143,6 +143,7 @@ int connection_close(server *srv, connection *con) {
                                "(warning) close:", con->fd, strerror(errno));
        }
 #endif
+       con->fd = -1;

        srv->cur_fds--;
 #if 0
@@ -1650,11 +1651,11 @@ int connection_state_machine(server *srv, connection *con) {
                    (con->traffic_limit_reached == 0)) {
                        fdevent_event_set(srv->ev, &(con->fde_ndx), con->fd, FDEVENT_OUT);
                } else {
-                       fdevent_event_del(srv->ev, &(con->fde_ndx), con->fd);
+                       fdevent_event_set(srv->ev, &(con->fde_ndx), con->fd, 0);
                }
                break;
        default:
-               fdevent_event_del(srv->ev, &(con->fde_ndx), con->fd);
+               fdevent_event_set(srv->ev, &(con->fde_ndx), con->fd, 0);
                break;
        }

diff --git a/src/fdevent.c b/src/fdevent.c
index e9038ab..0a9522e 100644
--- a/src/fdevent.c
+++ b/src/fdevent.c
@@ -165,6 +165,7 @@ int fdevent_event_del(fdevents *ev, int *fde_ndx, int fd) {

 int fdevent_event_set(fdevents *ev, int *fde_ndx, int fd, int events) {
        int fde = fde_ndx ? *fde_ndx : -1;
+       if (-1 == fd) return 0;

        if (ev->event_set) fde = ev->event_set(ev, fde, fd, events);
        ev->fdarray[fd]->events = events;

A slightly more efficient patch has been added to https://github.com/lighttpd/lighttpd1.4/pull/53

Applied in changeset 4b0c822ed0e00a5176d4da1827024f1751d3c508.