Added expired attribute to TaskTimeout

CHANGES

@@ -1,5 +1,34 @@
 CHANGES
 -------
+10/16/2016 Added an expired attribute to TaskTimeout exceptions
+           that more precisely indicates whether or not the
+           specified time internal has elapsed.  For example:
+
+           try:
+               await timeout_after(20, coro())
+           except TaskTimeout as e:
+               if e.expired:
+                   # 20 seconds have elapsed.
+                   ...
+               else:
+                   # Timeout has occurred early
+
+           A premature timeout can occur when timeouts are nested.
+           For example:
+
+           async with timeout_after(15):
+               statements
+               ...
+               try:
+                   await timeout_after(5, coro())
+               except TaskTimeout as e:
+                   if e.expired:
+                      # Inner timeout expired
+                   else:
+                      # Outer timeout must have expired
+               ...
+
+
 08/16/2016 Modified the Queue class so that the put() method can be used from either
            synchronous or asynchronous code.  For example:
 

curio/kernel.py

@@ -259,7 +259,7 @@ def _reschedule_task(task, value=None, exc=None):
         # and continue to run to perform cleanup actions.  However, it would
         # normally terminate shortly afterwards.   This method is also used to
         # raise timeouts.
-        def _cancel_task(task, exc=CancelledError):
+        def _cancel_task(task, exc=CancelledError, val=None):
             if task.terminated:
                 return True
 
@@ -286,7 +286,7 @@ def _cancel_task(task, exc=CancelledError):
             task.cancel_func()
 
             # Reschedule it with a pending exception
-            _reschedule_task(task, exc=exc(exc.__name__))
+            _reschedule_task(task, exc=exc(exc.__name__ if val is None else val))
             return True
 
         # Cleanup task.  This is called after the underlying coroutine has
@@ -592,7 +592,7 @@ def _trap_get_current(_):
                                     _reschedule_task(task, value=current_time)
                             else:
                                 if tm == task.timeout:
-                                    if (_cancel_task(task, exc=TaskTimeout)):
+                                    if (_cancel_task(task, exc=TaskTimeout, val=current_time)):
                                         task.timeout = None
                                     else:
                                         # Note: There is a possibility that a task will be

curio/task.py

@@ -230,6 +230,7 @@ async def __aenter__(self):
     async def __aexit__(self, ty, val, tb):
         await _unset_timeout(self._prior)
         if ty == TaskTimeout:
+            val.expired = val.args[0] >= self._clock
             self.result = self._timeout_result
             if self._ignore:
                 return True
@@ -238,7 +239,8 @@ async def _timeout_after_func(clock, coro, ignore=False, timeout_result=None):
     prior = await _set_timeout(clock)
     try:
         return await coro
-    except TaskTimeout:
+    except TaskTimeout as e:
+        e.expired = e.args[0] >= clock
         if not ignore:
             raise
         return timeout_result