Sometimes poll_capacity returns Ready(Some(0)) - in which case
caller will have no way to wait for the stream capacity to become available.
The previous attempt on the fix has addressed only a part of the problem.
The root cause - in a nutshell - is the race condition between the
application tasks that performs stream I/O and the task that serves
the underlying HTTP/2 connection. The application thread that is about
to send data calls reserve_capacity/poll_capacity, is provided
with some send capacity and proceeds to send_data.
Meanwhile the service thread may send some buffered data and/or
receive some window updates - either way the stream's effective
allocated send capacity may not change, but, since the capacity still
available, send_capacity_inc flag may be set.
The sending task calls send_data and uses the entire allocated
capacity, leaving the flag set. Next time poll_capacity returns
Ready(Some(0)).
This change sets the flag and dispatches the wakeup event only in
cases when the effective capacity reported by poll_capacity actually
increases.
Fixes #628
Sometimes
poll_capacityreturnsReady(Some(0))- in which case caller will have no way to wait for the stream capacity to become available. The previous attempt on the fix has addressed only a part of the problem.The root cause - in a nutshell - is the race condition between the application tasks that performs stream I/O and the task that serves the underlying HTTP/2 connection. The application thread that is about to send data calls
reserve_capacity/poll_capacity, is provided with some send capacity and proceeds tosend_data.Meanwhile the service thread may send some buffered data and/or receive some window updates - either way the stream's effective allocated send capacity may not change, but, since the capacity still available,
send_capacity_incflag may be set.The sending task calls
send_dataand uses the entire allocated capacity, leaving the flag set. Next timepoll_capacityreturnsReady(Some(0)).This change sets the flag and dispatches the wakeup event only in cases when the effective capacity reported by
poll_capacityactually increases.