iOS 移动开发网络 part5.2:CocoaAsyncSoc

_socket = [[GCDAsyncSocket alloc] initWithDelegate:self delegateQueue:dispatch_get_main_queue()];

- (id)initWithDelegate:(id<GCDAsyncSocketDelegate>)aDelegate delegateQueue:(dispatch_queue_t)dq socketQueue:(dispatch_queue_t)sq
{
    if((self = [super init]))
    {
        delegate = aDelegate;
        delegateQueue = dq;
        
        socket4FD = SOCKET_NULL;
        
        socketUrl = nil;
        stateIndex = 0;
        
        if (sq)
        {
            NSAssert(sq != dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_LOW, 0),
                     @"The given socketQueue parameter must not be a concurrent queue.");
            NSAssert(sq != dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0),
                     @"The given socketQueue parameter must not be a concurrent queue.");
            NSAssert(sq != dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0),
                     @"The given socketQueue parameter must not be a concurrent queue.");
            
            socketQueue = sq;
        }
        else
        {
            socketQueue = dispatch_queue_create([GCDAsyncSocketQueueName UTF8String], NULL);
        }
        
        IsOnSocketQueueOrTargetQueueKey = &IsOnSocketQueueOrTargetQueueKey;
        
        void *nonNullUnusedPointer = (__bridge void *)self;
        dispatch_queue_set_specific(socketQueue, IsOnSocketQueueOrTargetQueueKey, nonNullUnusedPointer, NULL);
        
        readQueue = [[NSMutableArray alloc] initWithCapacity:5];
        currentRead = nil;
        
        writeQueue = [[NSMutableArray alloc] initWithCapacity:5];
        currentWrite = nil;
        
        preBuffer = [[GCDAsyncSocketPreBuffer alloc] initWithCapacity:(1024 * 4)];
        alternateAddressDelay = 0.3;
    }
    return self;
}

GCDAsyncSocket创建完成,可以看出,初始化方法内_socket获取到了:

delegate
delegateQueue//调用delegate方法的队列
socketQueue//必须是串行队列,否则抛出异常;所有GCDAsyncSocket的读写全要在socketQueue内进行
readQueue
writeQueue
preBuffer//预备缓存块
alternateAddressDelay//DNS会返回连接的备选地址,首选地址连接失败后,延后连接备选地址,alternateAddressDelay就规定了延后多长时间发起第二次连接(连接备选地址的情况本文不会细作解析)
IsOnSocketQueueOrTargetQueueKey//所有GCDAsyncSocket的读写全要在socketQueue内进行,IsOnSocketQueueOrTargetQueueKey就是用于防止socketQueue重入的