GCD详情

#import "ViewController.h"

@interface ViewController ()

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.
    //1.多次执行相同的代码块
    [self testApply];
    //2.代码块只执行一次
    //[self testOnce];
    //[self testOnce];
    //[self testOnce];
    //[self testOnce];
    //3.代码块在一段时间后执行
    //[self testAfter];
    //4.将线程放到一个组里面
    //[self testGroup];
    //5.在两个线程序列之间执行一段代码
    //[self testBarrier];
}

//在两个线程序列之间执行一段代码
-(void)testBarrier
{
    //队列不能是系统的全局并行队列
    //使用自己创建的并行队列
    dispatch_queue_t conQueue = dispatch_queue_create("conQueue", DISPATCH_QUEUE_CONCURRENT);
    //线程一
    dispatch_async(conQueue, ^{
        for (int i=0; i<100; i++) {
            NSLog(@"线程一:%d",i);
        }
    });
    
    //线程二
    dispatch_async(conQueue, ^{
        for (int i=0; i<100; i++) {
            NSLog(@"线程二:%d",i);
        }
    });
    
    //在线程一,线程二执行完成之后,在线程三执行之前执行一段代码
    dispatch_barrier_async(conQueue, ^{
        NSLog(@"barrier");
    });
    
    //线程三
    dispatch_async(conQueue, ^{
        for (int i=0; i<100; i++) {
            NSLog(@"线程三:%d",i);
        }
    });
}

//将线程放到一个组里面
-(void)testGroup
{
    dispatch_group_t group = dispatch_group_create();
    //获取全局队列
    dispatch_queue_t globalQueue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
    //参数一:线程所在的组
    //参数二:线程所在的队列
    //参数三:线程的执行体
    //线程一
    dispatch_group_async(group, globalQueue, ^{
        for (int i=0; i<100; i++) {
            NSLog(@"线程一:%d",i);
        }
    });
    //线程二
    dispatch_group_async(group, globalQueue, ^{
        for (int i=0; i<100; i++) {
            NSLog(@"线程二:%d",i);
        }
    });
    
    
    dispatch_group_notify(group, globalQueue, ^{
        //在线程组里的所有线程执行完成后调用的代码
        NSLog(@"线程组执行完成");
    });
}

//代码块在一段时间后执行
-(void)testAfter
{
    NSLog(@"执行之前");
    //时间
    //当前时间十秒之后
    dispatch_time_t time = dispatch_time(DISPATCH_TIME_NOW, NSEC_PER_SEC*10);
    //参数一:时间
    //参数二:线程所在的队列
    //参数三:线程的执行体
    dispatch_after(time, dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
        NSLog(@"执行了after");
    });
}

//代码块只执行一次
-(void)testOnce
{
    static dispatch_once_t onceToken;
    
    dispatch_once(&onceToken,^{
        NSLog(@"执行一次");
    });
}

//多次执行相同的代码块
-(void)testApply
{
    //参数一:代码块执行的次数
    //参数二:代码块所在的队列
    //参数三:代码块的内容
    size_t t = 10;
    //队列
    dispatch_queue_t globalQueue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
    dispatch_apply(t, globalQueue, ^(size_t time) {
        NSLog(@"第%ld次",time);
    });
}

- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}

@end