Yesterday I checked in a new feature to stackless.
Tasklets now have a new function, "throw", which enhances the already present
tasklet.raise_exception().
The docstrings:
"tasklet.throw(exc, val, tb, immediate=True) -- raise an exception for the
tasklet.\n\
'exc', 'val' and 'tb' have the same semantics as Python's 'raise'
statement.\n\
If 'immediate' is True, the tasklet is immediately activated,
otherwise, it is\n\
merely made runnable");
This brings two new features:
a) unifies the argument semantics. It now takes the same three arguments
as a python "raise" expression, just like channel.send_throw() already does.
b) It allows the target to be scheduled, rather than invoked immediately.
This is useful in frameworks, for example to send a timeout error to a tasklet
without interrupting regular scheduling.
c) if the exception cannot be sent because the target is dead/not yet
running, then a RuntimeError is raised.
item c) is the reason we can't let the existing kill and raise_exception
methods use this. They have the confusing property that if the target is dead
or not running yet, the error will be raised on the main tasklet instead. I
actually think that this is a pretty bad idea. I wonder if anyone is depending
on this? If not, I can make kill and raise_exception a special case of the new
one.
(channel.send_throw() is also a fairly recent addition. An improvement on
channel.send_exception() it allows the user to send an existing excetption
instance, and a traceback, over the channel. It is particularly the sending of
tracebacks which is useful when handling errors.)
K
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