uasyncio.core: wait_for: Add support for cancelling I/O-bound coros.

Coros which removed from normal scheduling queue (and possibly put into another queue, like I/O queue here) are marked with .pend_throw(False). If wait_for() cancels such a coro, it is explicitly scheduled for execution, so they actually could process pending exception (coro's exception handler should take care of removing it from another queue and related clean up).

Author: pfalcon

uasyncio.core/uasyncio/core.py

@@ -104,9 +104,11 @@ def run_forever(self):
  if isinstance(ret, SleepMs):
  delay = arg
  elif isinstance(ret, IORead):
+ cb.pend_throw(False)
  self.add_reader(arg, cb)
  continue
  elif isinstance(ret, IOWrite):
+ cb.pend_throw(False)
  self.add_writer(arg, cb)
  continue
  elif isinstance(ret, IOReadDone):
@@ -242,7 +244,10 @@ def timeout_func(timeout_obj):
  if timeout_obj.coro:
  if __debug__ and DEBUG:
  log.debug("timeout_func: cancelling %s", timeout_obj.coro)
- timeout_obj.coro.pend_throw(TimeoutError())
+ prev = timeout_obj.coro.pend_throw(TimeoutError())
+ #print("prev pend", prev)
+ if prev is False:
+ _event_loop.call_soon(timeout_obj.coro)
 
  timeout_obj = TimeoutObj(_event_loop.cur_task)
  _event_loop.call_later_ms(timeout, timeout_func, timeout_obj)