单例

#import "NSObjectGCDAsyncSocket.h"@implementation NSObjectGCDAsyncSocket{    GCDAsyncSocket* socket;}/** *  单例 * *  @return */+(NSObjectGCDAsyncSocket *)defaultSocket{    //socket只会实例化一次    static NSObjectGCDAsyncSocket* socket=nil;    //保证线程安全，defaultSocket只执行一次    static dispatch_once_t once;    dispatch_once(&once, ^    {        socket=[[NSObjectGCDAsyncSocket alloc] init];    });    return socket;}/** *  初始化 * * *  @return self */-(instancetype)init{    self=[super init];    if (self)    {        socket=[[GCDAsyncSocket alloc] initWithDelegate:self                                          delegateQueue:dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0)];    }    return self;}