NSStream and Sockets, NSStreamDelegate methods not being called

Question

I've followed the guide Setting Up Socket Streams and have effectively duplicated that code in my class. No matter what I try the delegate methods just don't seem to get called.

In the header file I have (basically):

@interface myClass : NSObject <NSStreamDelegate> {
    NSInputStream *inputStream;
    NSOutputStream *outputStream;
}
- (void)connect;
@end;

The connect method:

- (void)connect {
    CFReadStreamRef readStream;
    CFWriteStreamRef writeStream;

    CFStreamCreatePairWithSocketToHost(kCFAllocatorDefault, (CFStringRef)@"host.example.com", 1234, &readStream, &writeStream);

    inputStream = (NSInputStream *)readStream;
    outputStream = (NSOutputStream *)writeStream;
    [inputStream setDelegate:self];
    [outputStream setDelegate:self];
    [inputStream scheduleInRunLoop:[NSRunLoop currentRunLoop] forMode:NSDefaultRunLoopMode];
    [outputStream scheduleInRunLoop:[NSRunLoop currentRunLoop] forMode:NSDefaultRunLoopMode];
    [inputStream open];
    [outputStream open];
}

Also tried using CFStreamCreatePairWithSocketToCFHost() and [NSStream getStreamsToHost:port:inputStream:outputStream: - all with exactly the same result.

I've set a breakpoint at the beginning of the connect method, stepped through every line and every pointer is valid and seems to point to the correct object.

In GDB, after the setDelegate calls, po [inputStream delegate] prints <myClass: 0x136380> as expected, so it has set the delegate correctly.

For the life of me I can't work out why it refuses to call the stream:handleEvent: method on my class:

- (void)stream:(NSStream *)aStream handleEvent:(NSStreamEvent)eventCode {
    NSLog(@"got an event");
}

Hopefully I've missed something really simple and obvious and a second pair of eyes can spot my mistake.

Thanks in advance to anyone who has the patience and taken the time to read this far!

Answer 1

In the lines like this:

[inputStream scheduleInRunLoop:[NSRunLoop currentRunLoop] forMode:NSDefaultRunLoopMode];

Instead of using [NSRunLoop currentRunLoop] I changed it to [NSRunLoop mainRunLoop].

EDIT 2011-05-30:

The reason this did not work is because I was setting up the sockets in a background thread via +[NSThread detachNewThreadSelector:toTarget:withObject:].

Doing it that way created a new run loop, which after reading the run loop developer documentation I discovered that you need to tell the NSRunLoop to run manually.

Running it in the same run loop as the main thread was fine on performance, though I was able to squeeze a bit more performance out by writing a wrapper class and running all network I/O on a background thread.

Answer 2

That solution will work if & only if you don't have blocking work on thread 0. This is often OK, but a better solution is to create a new thread (i.e. using a class method to create the thread on demand) and then enqueue on that thread. i.e.

+ (NSThread *)networkThread {
    static NSThread *networkThread = nil;
    static dispatch_once_t oncePredicate;

    dispatch_once(&oncePredicate, ^{
        networkThread =
             [[NSThread alloc] initWithTarget:self
                                     selector:@selector(networkThreadMain:)
                                       object:nil];
        [networkThread start];
    });

    return networkThread;
}

+ (void)networkThreadMain:(id)unused {
    do {
        @autoreleasepool {
            [[NSRunLoop currentRunLoop] run];
        }
    } while (YES);
}

- (void)scheduleInCurrentThread
{
    [inputstream scheduleInRunLoop:[NSRunLoop currentRunLoop]
                           forMode:NSRunLoopCommonModes];
}

With this, you can schedule the input stream using:

[self performSelector:@selector(scheduleInCurrentThread)
             onThread:[[self class] networkThread]
           withObject:nil
        waitUntilDone:YES];

This will allow you to run your network operations without worrying about deadlocks anymore.