多线程GCD笔记

• 同步函数 + 主队列
• 异步函数 + 主队列
• 同步函数 + 串行队列
• 异步函数 + 串行队列
• 同步函数 + 并发队列
• 异步函数 + 并发队列
• 线程间通信
• dispatch_barrier_async(栅栏)
• dispatch_after 延迟执行
• dispatch_apply 多线程遍历
• dispatch_once
• dispatch_async_f
• dispatch_group
• dispatch_source定时器
• dispatch_group_enter/dispatch_group_leave/dispatch_group_notify

• 同步函数 + 主队列：
  执行dispatch_sync时主线程堵塞
  执行结果:Thread ----- begin
  -(void)thread {

NSLog(@"Thread ----- begin");
// 1.获得主队列
dispatch_queue_t queue = dispatch_get_main_queue();
// 2.将任务加入队列
dispatch_sync(queue, ^{
    NSLog(@"%@", [NSThread currentThread]);
});
NSLog(@"Thread ----- end");

}

• 异步函数 + 主队列：只在主线程中执行任务

因为是在主线程中,所以1-7任务按顺序执行
执行结果:
Thread ----- begin
Thread ----- end
1-----{number = 1, name = main}
2-----{number = 1, name = main}
3-----{number = 1, name = main}
4-----{number = 1, name = main}
5-----{number = 1, name = main}
6-----{number = 1, name = main}
7-----{number = 1, name = main}
-(void)thread {

NSLog(@"Thread ----- begin");
// 1.获得主队列
dispatch_queue_t queue = dispatch_get_main_queue();

// 2.将任务加入队列
dispatch_async(queue, ^{
    NSLog(@"1-----%@", [NSThread currentThread]);
});
dispatch_async(queue, ^{
    NSLog(@"2-----%@", [NSThread currentThread]);
});
dispatch_async(queue, ^{
    NSLog(@"3-----%@", [NSThread currentThread]);
});
dispatch_async(queue, ^{
    sleep(1.0);
    NSLog(@"4-----%@", [NSThread currentThread]);
});
dispatch_async(queue, ^{
    NSLog(@"5-----%@", [NSThread currentThread]);
});
dispatch_async(queue, ^{
    NSLog(@"6-----%@", [NSThread currentThread]);
});
dispatch_async(queue, ^{
    NSLog(@"7-----%@", [NSThread currentThread]);
});
NSLog(@"Thread ----- end");

}

• 同步函数 + 串行队列：不会开启新的线程，thread方法所在的线程是main。任务是串行的，执行完1任务，再执2任务,按顺序执行

执行结果:
Thread ----- begin
1-----{number = 1, name = main}
2-----{number = 1, name = main}
Thread ----- end
-(void)thread {

NSLog(@"Thread ----- begin");
// 1.创建串行队列
dispatch_queue_t queue = dispatch_queue_create("queue", DISPATCH_QUEUE_SERIAL);

// 2.将任务加入队列
dispatch_sync(queue, ^{
    NSLog(@"1-----%@", [NSThread currentThread]);
});
dispatch_sync(queue, ^{
    NSLog(@"2-----%@", [NSThread currentThread]);
});
NSLog(@"Thread ----- end");

}

• 异步函数 + 串行队列：会开启新的线程，但是任务是串行的，执行完1任务，再执行2任务,按顺序执行
  执行结果:

Thread ----- begin
Thread ----- end
1-----{number = 3, name = (null)}
2-----{number = 3, name = (null)}
-(void)thread {

NSLog(@"Thread ----- begin");
// 1.创建串行队列
dispatch_queue_t queue = dispatch_queue_create("queue", DISPATCH_QUEUE_SERIAL);

// 2.将任务加入队列
dispatch_async(queue, ^{
    NSLog(@"1-----%@", [NSThread currentThread]);
});
dispatch_async(queue, ^{
    NSLog(@"2-----%@", [NSThread currentThread]);
});
NSLog(@"Thread ----- end");

}

• 同步函数 + 并发队列：不会开启新的线程,在thread方法所在的线程中,按顺序执行1,2任务

DISPATCH_QUEUE_PRIORITY_DEFAULT:默认优先级
执行结果:
Thread ----- begin
1-----{number = 3, name = thread1}
2-----{number = 3, name = thread1}
Thread ----- end
-(void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event{

NSThread *thread = [[NSThread alloc] initWithTarget:self selector:@selector(thread) object:nil];
thread.name = @"thread1";
[thread start];

}

-(void)thread{

NSLog(@"Thread ----- begin");
// 1.获得全局的并发队列
dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);

// 2.将任务加入队列
dispatch_sync(queue, ^{
    NSLog(@"1-----%@", [NSThread currentThread]);
});
dispatch_sync(queue, ^{
    NSLog(@"2-----%@", [NSThread currentThread]);
});
NSLog(@"Thread ----- end");

}

• 异步函数 + 并发队列：可以同时开启多条线程

执行结果:
Thread ----- begin
Thread ----- end
1-----{number = 3, name = (null)}
2-----{number = 2, name = (null)}
1-----{number = 3, name = (null)}
2-----{number = 2, name = (null)}
-(void)thread {

NSLog(@"Thread ----- begin");
// 1.获得全局的并发队列
dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);

// 2.将任务加入队列
dispatch_async(queue, ^{
    for (NSInteger i = 0; i<2; i++) {
        NSLog(@"1-----%@", [NSThread currentThread]);
    }
});
dispatch_async(queue, ^{
    for (NSInteger i = 0; i<2; i++) {
        NSLog(@"2-----%@", [NSThread currentThread]);
    }
});
NSLog(@"Thread ----- end");

}

线程间通信

－(void)thread {

dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
    //耗时操作
    dispatch_async(dispatch_get_main_queue(), ^{
        //回到主线程,更新UI
    });
});

｝

dispatch_barrier_async:

dispatch_barrier_async，可以翻译成栅栏（barrier）
barrier作为流程控制的一种方式是用在并行环境当中。

以barrier任务为分界线,先执行barrier之前的任务1,2(1,2执行顺序不确定),在执行3,4(3,4执行顺序不确定)
执行结果:
----2-----{number = 6, name = (null)}
----1-----{number = 5, name = (null)}
----barrier-----{number = 5, name = (null)}
----3-----{number = 5, name = (null)}
----4-----{number = 6, name = (null)}
-(void)barrier {

dispatch_queue_t queue = dispatch_queue_create("queue", DISPATCH_QUEUE_CONCURRENT);

dispatch_async(queue, ^{
    NSLog(@"----1-----%@", [NSThread currentThread]);
});
dispatch_async(queue, ^{
    NSLog(@"----2-----%@", [NSThread currentThread]);
});

dispatch_barrier_async(queue, ^{
    NSLog(@"----barrier-----%@", [NSThread currentThread]);
});

dispatch_async(queue, ^{
    NSLog(@"----3-----%@", [NSThread currentThread]);
});
dispatch_async(queue, ^{
    NSLog(@"----4-----%@", [NSThread currentThread]);
});

}

注释掉dispatch_barrier_async后任务1-4执行顺序无序
执行结果:
----1-----{number = 3, name = (null)}
----4-----{number = 5, name = (null)}
----3-----{number = 4, name = (null)}
----2-----{number = 2, name = (null)}
-(void)barrier {

dispatch_queue_t queue = dispatch_queue_create("queue", DISPATCH_QUEUE_CONCURRENT);

dispatch_async(queue, ^{
    NSLog(@"----1-----%@", [NSThread currentThread]);
});
dispatch_async(queue, ^{
    NSLog(@"----2-----%@", [NSThread currentThread]);
});

// dispatch_barrier_async(queue, ^{
// NSLog(@"----barrier-----%@", [NSThread currentThread]);
// });

dispatch_async(queue, ^{
    NSLog(@"----3-----%@", [NSThread currentThread]);
});
dispatch_async(queue, ^{
    NSLog(@"----4-----%@", [NSThread currentThread]);
});

}

延迟执行

＃define DISPATCH_TIME_NOW (0ull) : unsigned long long 类型的0
＃define NSEC_PER_SEC 1000000000ull : unsigned long long 类型的1000000000
dispatch_after:不是一定时间后执行相应的任务，而是一定时间后，将执行的操作加入到队列中（队列里面再分配执行的时间）所以在比如主线程每隔1/60秒执行的RunLoop，Block最快在2秒后执行，最慢在 2+1/60秒后执行。

非阻塞的执行方式,延时2秒,dispatch_get_main_queue()主线程中执行

    CGFloat t = 2.0;
    dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(t * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{

    });

• Swift延时执行方法
  let time: NSTimeInterval = 2.0
  let delay = dispatch_time(DISPATCH_TIME_NOW,
  Int64(time * Double(NSEC_PER_SEC)))
  dispatch_after(delay, dispatch_get_main_queue()) {

  }
  

• 其他延时方法:

此方式要求必须在主线程中执行，否则无效。
是一种非阻塞的执行方式，
可以通过NSTimer类的- (void)invalidate;取消执行。
repeats:是否重复执行
-(void)timer{

 [NSTimer scheduledTimerWithTimeInterval:2.0f target:self selector:@selector(running) userInfo:nil repeats:NO];  

}

此方式要求必须在主线程中执行，否则无效。
是一种非阻塞的执行方式
-(void)timer{

 [self performSelector:@selector(running) withObject:nil afterDelay:2.0f];

}

dispatch_apply

第一个参数是迭代次数(这里便利10次)，第二个是所在的队列(queue)，第三个是当前索引(index)
dispatch_apply 和 dispatch_apply_f 是同步函数,会阻塞当前线程直到所有循环迭代执行完成。当提交到并发queue时,循环迭代的执行顺序是不确定的
执行结果:
{number = 1, name = main}, arr[0]:11
{number = 3, name = (null)}, arr[1]:12
{number = 4, name = (null)}, arr[3]:14
{number = 2, name = (null)}, arr[2]:13
{number = 3, name = (null)}, arr[5]:16
{number = 4, name = (null)}, arr[6]:17
{number = 1, name = main}, arr[4]:15
{number = 2, name = (null)}, arr[7]:18
{number = 3, name = (null)}, arr[8]:19
{number = 4, name = (null)}, arr[9]:20

dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
NSArray *arr = @[@"11",@"12",@"13",@"14",@"15",@"16",@"17",@"18",@"19",@"20"];
dispatch_apply(arr.count, queue, ^(size_t index) {
    NSLog(@"%@, arr[%zu]:%@", [NSThread currentThread], index, arr[index]);
});

dispatch_once

dispatch_once不仅意味着代码仅会被运行一次，而且还是线程安全的，这就意味着你不需要使用诸如@synchronized之类的来防止使用多个线程或者队列时不同步的问题。

static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{
    //程序运行期间只会执行一次
});

利用dispatch_once创建单例模式
static id _instance;
+(instancetype)allocWithZone:(struct _NSZone *)zone{

static dispatch_once_t onceToken;//记录是否执行了block
dispatch_once(&onceToken, ^{
    _instance = [super allocWithZone:zone];
});
return _instance;

}
+(instancetype)shareInstance{

static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{
    _instance = [[self alloc] init];
});
return _instance;

}
-(id)copyWithZone:(NSZone *)zone{

return _instance;

}

dispatch_async_f

一般用dispatch_async(block)。dispatch_async_f(函数)
执行结果:dsafasd

-(void)asuncf{

dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
NSString *str = @"dsafasd";
dispatch_async_f(queue, (__bridge void *)(str), download);

}

void download(void * data)
{
NSLog(@"%@", data);
}

dispatch_group

因为是在并行队列上执行，追加字符串的2个任务执行顺不不确定,当并行队列全部执行完成后，最后到dispatch_group_notify执行操作。

执行结果:123456
＃import "ViewController.h"
@interface ViewController ()
@property (nonatomic, copy) NSString *str;
@end
-(void)group {

// 获取全局列组
dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
// 创建一个队列组
dispatch_group_t group = dispatch_group_create();
self.str = @"";
dispatch_group_async(group, queue, ^{
   self.str = [self.str stringByAppendingString:@"123"];
});

dispatch_group_async(group, queue, ^{
    self.str = [self.str stringByAppendingString:@"456"];
});

dispatch_group_notify(group, queue, ^{
    NSLog(@"%@", self.str);
    dispatch_async(dispatch_get_main_queue(), ^{
        //主线程操作
    });
});

}

dispatch_source定时器

-(void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event
{
dispatch_queue_t queue = dispatch_get_main_queue();

// 创建一个定时器(dispatch_source_t本质还是个OC对象)
self.timer = dispatch_source_create(DISPATCH_SOURCE_TYPE_TIMER, 0, 0, queue);

// 设置定时器的各种属性（几时开始任务，每隔多长时间执行一次）
// GCD的时间参数，一般是纳秒（1秒 == 10的9次方纳秒）
// 何时开始执行第一个任务
// dispatch_time(DISPATCH_TIME_NOW, 1.0 * NSEC_PER_SEC) 比当前时间晚3秒
dispatch_time_t start = dispatch_time(DISPATCH_TIME_NOW, (int64_t)(1.0 * NSEC_PER_SEC));
uint64_t interval = (uint64_t)(1.0 * NSEC_PER_SEC);
dispatch_source_set_timer(self.timer, start, interval, 0);

// 设置回调
dispatch_source_set_event_handler(self.timer, ^{
    NSLog(@"------------%@", [NSThread currentThread]);
});

// 启动定时器
dispatch_resume(self.timer);
}

dispatch_group_enter/dispatch_group_leave/dispatch_group_notify

    目的:所有操作执行完成后再执行dispatch_group_notify内的任务
    // 1.创建一个组
    let group = dispatch_group_create()
    // 2.将操作添加到组中
    dispatch_group_enter(group)
    //3.要执行的操作。。。。
    // 4.离开当前组
    dispatch_group_leave(group)
    //5.所有操作完成后执行
    dispatch_group_notify(group, dispatch_get_main_queue()) { () -> Void in
    }