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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.
When it's message queue reaches that limit (settable with setActorQueueLimit:),
calling threads will be paused.
FutureProxy
A future is a transparent proxy for the result which, when accessed before the
result is ready, will pauses calling threads 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 an instance.
To Do
- handle BatchProxy exceptions
- make sure all locks deal with exceptions
- future notifications of some kind
- more tests
- convenience methods for returning NSNumbers instead of C types
- convenience methods for performing blocking ops via single calls to instance methods
- auto deadlock detection for actor queue limit, synchronous and batches
- add a total queue and/or total actor limits
- better respondsToSelector implementation
- chainable batch groups with in, out, and error queues
Credits
Thanks to Mark Papadakis for tips on mutex conditions.
IIRC I saw the BatchProxy pattern first used in Io by quag.
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