dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
NSString *urlString = @"http://img0.pconline.com.cn/pconline/1111/28/2601303_p2.jpg";
NSURL *url = [NSURL URLWithString:urlString];
NSData *sData = [NSData dataWithContentsOfURL:url];
if(sData && sData.length > 0)
{
dispatch_async(dispatch_get_main_queue(), ^(void){
NSLog(@">>>>>>>>>>main queue");
});
}
});
1。GCD之dispatch queue
http://www.cnblogs.com/scorpiozj/archive/2011/07/25/2116459.html
2。iOS中GCD的魔力
http://blog.csdn.net/favormm/article/details/6453260
3。官方 ，内容真的很多
http://developer.apple.com/library/ios/#documentation/Performance/Reference/GCD_libdispatch_Ref/Reference/reference.html
http://developer.apple.com/library/ios/#documentation/General/Conceptual/ConcurrencyProgrammingGuide/OperationQueues/OperationQueues.html#//apple_ref/doc/uid/TP40008091-CH102-SW1
4.详解IOS开发应用之并发Dispatch Queues
http://mobile.51cto.com/iphone-283323.htm
5。斯坦福大学关于gcd的讲义
http://www.stanford.edu/class/cs193p/cgi-bin/drupal/system/files/lectures/Lecture 13_0.pdf
gcd其实就是牛逼简化版的多线程。gcd和block是亲兄弟，所以学习gcd前需要了解block，不知道也没事，看看代码就明白了。