Re: Waiting on multiple blocking events

Yang Zhang wrote:
> Mike Abbott wrote:
>>> Is there a way to "compose" together multiple blocking operations? 
>>
>> Sounds interesting, kinda like what kqueue()/kevent() do:  one-stop
>> event processing.  "Block this thread until one of this laundry list of
>> disparate events fires."  Do you have a prototype implementation you'd
>> like to contribute to the project, or wrappers you'd contribute to its
>> "extensions" library?
> 
> I have a poor man's implementation of "cleanly interruptible points." 
> This involves primitives called "hubs" (sets of threads) that threads 
> may join and other threads may signal.  It's similar to a condition 
> variable, but signaling results in interrupting the thread from its 
> current blocking operation.
> 
>   {
>     st_intr intr(hub);
>     int ret = st_read_fully(...);
>     if (ret == EINT) ...
>     ...
>   }
> 
> This turned out to be suitable enough for my purposes.  The code is all 
> available in my little header of ST tools:
> 
> http://assorted.svn.sf.net/viewvc/assorted/cpp-commons/trunk/src/commons/st/st.h?revision=1077&view=markup 
> 
> 
> I thought about my more general suggestion some more.  You can implement 
> any() atop ST by starting a thread for each blocking operation involved 
> in the any(), wrapping them in functions that - on finishing - interrupt 
> the other threads (using something similar to the above mechanism, on a 
> hub created locally by the any() call), informing them that they're the 
> losers (so that they may properly react/clean up), and also notifying 
> the parent thread of its own success and return value.

Forgot to add: such an implementation would be much more expensive than 
it needs to be, since it's actually creating a separate thread per 
blocking operation, when in fact you shouldn't really need to do this if 
you're willing to modify ST to explicitly support such operation.

> 
>>
>>
>>
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> 


-- 
Yang Zhang
http://www.mit.edu/~y_z/

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