Great explanation. Thanks! Jason
On Wed, Jan 12, 2011 at 4:40 PM, <exar...@twistedmatrix.com> wrote: > Some reactors have a different implementation of wakeUp than the above, > but they all have the same goal. > > The reactor thread may be doing something which is going to block > indefinitely (WaitForMultipleObjects, select(), epoll_wait(), etc). The > purpose of the wakeUp call is to cause that blocking call to end. Once > it ends, calls in the threadCallQueue can be processed. > > The reactor is written such that if you are running code in the same > thread it is running in (ie, you are "in the reactor thread") then any > event source you create (be it network or time or whatever), the reactor > will be sure to service it in a timely manner. For network event > sources, this means it will include a descriptor in the select() (etc) > call. For timing event sources (ie callLater), it means the reactor > will set a timeout on the select() (etc) call so that it returns before > it is time for that delayed call to execute. > > However, if you are not in the reactor thread, then really the only > thing you're allowed to do to Twisted is use reactor.callFromThread. > Since this might happen at any time with respect to what the reactor > thread is doing, there's no way to be sure a (let's call it a) thread > call event will get handled in a timely fashion. So this is the problem > that wakeUp solves. After the thread call event is added to > threadCallQueue, wakeUp makes some event source the reactor is > monitoring signal readiness (on POSIX, it writes a byte to a pipe the > reactor is select()ing (etc) on; on Windows, it posts an event like you > pasted above). This ensures that if the reactor is asleep waiting for > an event it will wake up soon, and then it will notice there are thread > call events to process. > > Jean-Paul > > _______________________________________________ > Twisted-Python mailing list > Twisted-Python@twistedmatrix.com > http://twistedmatrix.com/cgi-bin/mailman/listinfo/twisted-python > -- Jason Rennie Research Scientist, ITA Software 617-714-2645 http://www.itasoftware.com/
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