Multithreaded actors and futures for Objective-C
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About ActorKit is a framework for multithreaded actors with transparent futures in Objective-C. ActorProxy Sending an "asActor" message to any object returns an actor proxy for the object. Sending messages to the actor will queue them to be processed in first-in-first-out order by the actor's thread and immediately returns a "future" object. If its message queue exceeds a given limit (set with setActorQueueLimit:), the calling threads that exceeded the limit will be paused until the more of the queue is processed. FutureProxy A future is a transparent proxy for the result which, when accessed before the result is ready, pauses any threads attempting to access it until it is ready. Futures auto detect and raise an exception in deadlock situations. Example // the fetch return a future immediately NSData *aFuture = [(NSURL *)[[@"http://yahoo.com" asURL] asActor] fetch]; // ... do stuff ... // now when we try to access the values, // the thread waits if the values aren't ready NSLog(@"request returned %i bytes", (int)[aFuture length]); ThreadSafeProxy Calling asThreadSafe on any object returns a proxy that ensures only one thread can access it at a time. Example: NSMutableDictionary *dict = [[NSMutableDictionary dictionary] asThreadSafe]; BatchProxy Calling asBatch on an NSArray returns a BatchProxy which can be used to do a parallel "map" using GCD (BSD workerqueues). Example: NSArray *results = [[urls asBatch] fetch]; Sends concurrent fetch messages to each element of the urls array and returns an array containing the results. Notes Exceptions that occur while an actor processes a message will be passed to the future and raised in all the threads that attempt to access the future. It's ok for multiple threads to look at the same future. ActorKit does no busy waits. Objects store their proxies as an associated objects so the same proxy is returned for a given instance. To Do - handle BatchProxy exceptions - make sure all locks deal with exceptions - future notifications of some kind - more tests - auto deadlock detection for actor queue limit and batches - add a total queue and/or total actor limits - better respondsToSelector implementation - (maybe) chainable persistent batch groups with in, out, and error queues - (maybe) integrate with distibuted objects to allow bundles and data to be distributed... - (maybe) explore synchronization via ownership Credits Thanks to Mark Papadakis for tips on mutex conditions. IIRC I saw the BatchProxy pattern first used in Io by quag.