ZMQContext locks around sockets array mutations.

README.mkd

@@ -10,3 +10,53 @@ laid out by the official
 
 [zmq-docs]: http://api.zeromq.org/zmq.html (zmq(7) Manual Page)
 [binding-zmq]: http://www.zeromq.org/guidelines:bindings (Guidelines for ZeroMQ Bindings)
+
+Documentation
+-------------
+Refer to the [ZeroMQ manual pages][zmq-docs].
+The Objective-C binding
+maintains a bit more state
+than the C API exposes,
+in that you can query
+a `ZMQContext`
+for its sockets
+and query a `ZMQSocket`
+for its context.
+
+Thread Safety
+-------------
+ZeroMQ has some restrictive thread safety and coupling issues:
+
+* Sockets can only be used from the thread that created them.
+* All ZMQ sockets provided in a single call to `zmq_poll()` must have been created using the same context.
+
+Because sockets
+are coupled to contexts
+for polling,
+you have to track
+each socket's context
+and make sure not to mix them.
+(The `ZMQSocket` class tracks this for you.)
+
+Because each socket
+is bound to the thread that created it,
+you must be very careful when using
+ZeroMQ sockets
+with Grand Central Dispatch
+or `NSOperationQueue`.
+The only persistent thread
+that these two expose
+is the thread
+you're least likely
+to want to perform socket operations on:
+the main thread.
+
+To Do
+-----
+* Add functional tests in the form of sample code.
+* Provide a more (Core)Foundation-like API
+(CFSocket, CFFileDescriptor)
+that takes advantage of the runloop.
+This is complicated by
+the threading constraints
+present in libzmq-2.0.7.

src/ZMQContext.h

@@ -1,9 +1,11 @@
 #import <Foundation/Foundation.h>
 #import "ZMQSocket.h"  // ZMQSocketType
+#import <libkern/OSAtomic.h>
 
 @interface ZMQContext : NSObject {
 	void *context;
 	NSMutableArray *sockets;
+	OSSpinLock socketsLock;
 	BOOL terminated;
 }
 + (void)getZMQVersionMajor:(int *)major minor:(int *)minor patch:(int *)patch;

src/ZMQContext.m

@@ -27,6 +27,7 @@ - (id)initWithIOThreads:(NSUInteger)threadCount {
 		return nil;
 	}
 
+	socketsLock = OS_SPINLOCK_INIT;
 	sockets = [[NSMutableArray alloc] init];
 	return self;
 }
@@ -44,7 +45,9 @@ - (ZMQSocket *)socketWithType:(ZMQSocketType)type {
 	ZMQSocket *
 	socket = [[[ZMQSocket alloc] initWithContext:self type:type] autorelease];
 	if (socket) {
-		[(NSMutableArray *)self.sockets addObject:socket];
+		OSSpinLockLock(&socketsLock); {
+			[(NSMutableArray *)self.sockets addObject:socket];
+		} OSSpinLockUnlock(&socketsLock);
 	}
 	return socket;
 }