“这是我参与8月更文挑战的第5天，活动详情查看：8月更文挑战”

一.主队列同步

/**
 主队列同步
 不会开线程
 */
- (void)mainSyncTest{
    
    NSLog(@"0");
    // 等 死锁
    dispatch_sync(dispatch_get_main_queue(), ^{
        NSLog(@"1");
        NSLog(@"%@",[NSThread currentThread]);
    });
    NSLog(@"2");
}
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二.主队列异步

/**
 主队列异步
 不会开线程 顺序
 */
- (void)mainAsyncTest{
    
    NSLog(@"0");
    dispatch_async(dispatch_get_main_queue(), ^{
        NSLog(@"1");
        NSLog(@"%@",[NSThread currentThread]);
    });
    NSLog(@"2");
}
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运行打印结果

三.全局队列同步

/**
 全局同步
 全局队列:一个并发队列 同步在主线程
 */
- (void)globalSyncTest{
    for (int i = 0; i<10; i++) {
        dispatch_sync(dispatch_get_global_queue(0, 0), ^{
            NSLog(@"%d-%@",i,[NSThread currentThread]);
        });
    }
    NSLog(@"hello queue");
}
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四.全局列异步

/**
 全局异步
 全局队列:一个并发队列
 */
- (void)globalAsyncTest{
    
    for (int i = 0; i<10; i++) {
        dispatch_async(dispatch_get_global_queue(0, 0), ^{
            NSLog(@"%d-%@",i,[NSThread currentThread]);
        });
    }
    NSLog(@"hello queue");
}

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五.自定义串行队列同步

/**
 串行同步队列 : FIFO: 先进先出 (在当前线程执行)
 */
- (void)serialSyncTest{
    //1:创建串行队列
    NSLog(@"hello");
    dispatch_queue_t queue = dispatch_queue_create("test", DISPATCH_QUEUE_SERIAL);
    for (int i = 0; i<10; i++) {
        dispatch_sync(queue, ^{
            NSLog(@"%d-%@",i,[NSThread currentThread]);
        });
    }
    NSLog(@"queue");

}
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六.自定义串行队列异步

/**
 串行异步队列 (开启一条线程 任务一个接一个)
 */
- (void)serialAsyncTest{
    //1:创建串行队列
    NSLog(@"hello");
    dispatch_queue_t queue = dispatch_queue_create("test", DISPATCH_QUEUE_SERIAL);
    for (int i = 0; i<100; i++) {
        dispatch_async(queue, ^{
            NSLog(@"%d-%@",i,[NSThread currentThread]);
        });
    }
    
    NSLog(@"queue");
}
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七.自定义并发队列同步

/**
 同步并发 : 堵塞 同步锁  队列 : resume supend   线程 操作, 队列挂起 任务能否执行 （不会开启线程 在当前线程执行）
 */
- (void)concurrentSyncTest{

    NSLog(@"hello");
    //1:创建并发队列
    dispatch_queue_t queue = dispatch_queue_create("test", DISPATCH_QUEUE_CONCURRENT);
    for (int i = 0; i<10; i++) {
        dispatch_sync(queue, ^{
            NSLog(@"%d-%@",i,[NSThread currentThread]);
        });
    }
    NSLog(@"queue");
}
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八.自定义并发队列异步

/**
 异步并发: 有了异步函数不一定开辟线程(开启线程 在当前线程执行)
 */
- (void)concurrentAsyncTest{
    
    NSLog(@"hello");
    //1:创建并发队列
    dispatch_queue_t queue = dispatch_queue_create("test", DISPATCH_QUEUE_CONCURRENT);
    for (int i = 0; i<100; i++) {
        dispatch_async(queue, ^{
            NSLog(@"%d-%@",i,[NSThread currentThread]);
        });
    }
    NSLog(@"queue");
}
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九.并发队列-异步-同步

- (void)concurrentASync_Sync{
    // 同步队列
    dispatch_queue_t queue = dispatch_queue_create("test", DISPATCH_QUEUE_CONCURRENT);
    NSLog(@"1");
    // 异步函数
    dispatch_async(queue, ^{
        NSLog(@"2");
        // 同步
        dispatch_sync(queue, ^{
            NSLog(@"3");
        });
        NSLog(@"4");
    });
    NSLog(@"5");

}
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运行结果打印

十.并发队列-异步-异步

- (void)concurrentASync_ASync{
    
    dispatch_queue_t queue = dispatch_queue_create("test", DISPATCH_QUEUE_CONCURRENT);
    NSLog(@"1");
    // 耗时
    dispatch_async(queue, ^{
        NSLog(@"2");
        dispatch_async(queue, ^{
            NSLog(@"3");
        });
        NSLog(@"4");
    });

    NSLog(@"5");

}
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运行结果打印

十一.并发队列-同步-同步

- (void)concurrentSync_Sync{
    // 同步队列
    dispatch_queue_t queue = dispatch_queue_create("test", DISPATCH_QUEUE_CONCURRENT);
    NSLog(@"1");
    // 异步函数
    dispatch_sync(queue, ^{
        NSLog(@"2");
        // 同步
        dispatch_sync(queue, ^{
            NSLog(@"3");
        });
        NSLog(@"4");
    });
    NSLog(@"5");

}
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运行结果打印

十二.并发队列-同步-异步

- (void)concurrentSync_ASync{
    
    dispatch_queue_t queue = dispatch_queue_create("test", DISPATCH_QUEUE_CONCURRENT);
    NSLog(@"1");
    // 耗时
    dispatch_sync(queue, ^{
        NSLog(@"2");
        dispatch_async(queue, ^{
            NSLog(@"3");
        });
        NSLog(@"4");
    });

    NSLog(@"5");

}
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运行结果打印

十三.串行队列-异步-同步

- (void)serialAsync_Sync{
    
    dispatch_queue_t queue = dispatch_queue_create("test", DISPATCH_QUEUE_SERIAL);
    NSLog(@"1");
    dispatch_async(queue, ^{
        NSLog(@"2");
        //死锁
        dispatch_sync(queue, ^{
            NSLog(@"3");
        });
        NSLog(@"4");
    });
    NSLog(@"5");
}
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运行结果打印

十四.串行队列-异步-异步

- (void)serialAsync_ASync{
    
    dispatch_queue_t queue = dispatch_queue_create("test", DISPATCH_QUEUE_SERIAL);
    NSLog(@"1");
    dispatch_async(queue, ^{
        NSLog(@"2");
        dispatch_async(queue, ^{
            NSLog(@"3");
        });
        NSLog(@"4");
    });
    NSLog(@"5");
}
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运行结果打印

十五.串行队列-同步-异步

 dispatch_queue_t queue = dispatch_queue_create("test", DISPATCH_QUEUE_SERIAL);
    NSLog(@"1");
    dispatch_sync(queue, ^{
        NSLog(@"2");
        dispatch_async(queue, ^{
            NSLog(@"3");
        });
        NSLog(@"4");
    });
    NSLog(@"5");
}
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运行结果打印

十六.串行队列-同步-同步

 dispatch_queue_t queue = dispatch_queue_create("test", DISPATCH_QUEUE_SERIAL);
    NSLog(@"1");
    dispatch_sync(queue, ^{
        NSLog(@"2");
        //死锁
        dispatch_sync(queue, ^{
            NSLog(@"3");
        });
        NSLog(@"4");
    });
    NSLog(@"5");
}
}
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运行结果打印

十七.并发——dispatch_barrier_sync

-(void)concurrent_barrierSync
{
    dispatch_queue_t concurrentQueue = dispatch_queue_create("test", DISPATCH_QUEUE_CONCURRENT);
        
        for (NSInteger i = 0; i < 10; i++) {
            dispatch_sync(concurrentQueue, ^{
                
                NSLog(@"%zd",i);
            });
        }
        
        dispatch_barrier_sync(concurrentQueue, ^{
           
            NSLog(@"barrier");
        });
        
        for (NSInteger i = 10; i < 20; i++) {
            
            dispatch_sync(concurrentQueue, ^{
                
                NSLog(@"%zd",i);
            });
        }
}
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十八.并发——dispatch_barrier_async

-(void)concurrent_barrierASync
{
    dispatch_queue_t concurrentQueue = dispatch_queue_create("test", DISPATCH_QUEUE_CONCURRENT);
        
        for (NSInteger i = 0; i < 10; i++) {
            
            dispatch_sync(concurrentQueue, ^{
                
                NSLog(@"%zd",i);
            });
        }
        
        dispatch_barrier_async(concurrentQueue, ^{
           
            NSLog(@"barrier");
        });
        
        for (NSInteger i = 10; i < 20; i++) {
            
            dispatch_sync(concurrentQueue, ^{
                
                NSLog(@"%zd",i);
            });
        }
}
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十七.个别案例

1.面试题1

-(void)perform {
    dispatch_async(dispatch_get_global_queue(0, 0), ^{
        [self performSelector:@selector(test) withObject:nil afterDelay:0];
    });
}
-(void)test{
    NSLog(@"hello word");
}
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不会打印hello word 这个方法要创建提交任务到runloop上的，而gcd底层创建的线程是默认没有开启对应runloop的，所有这个方法就会失效。
以下4种解决方式：

• 1.将dispatch_get_global_queue改成dispatch_get_main_queue()，由于主队列所在的主线程是默认开启了runloop的
• 2.将dispatch_async改成dispatch_sync，因为同步是在当前线程执行，那么如果当前线程是主线程，test方法也是会去执行的
• 3.添加runloop线程保活

 -(void)perform {
     dispatch_async(dispatch_get_global_queue(0, 0), ^{
         [[NSRunLoop currentRunLoop] addPort:[NSPort new] forMode:NSRunLoopCommonModes];
         [self performSelector:@selector(test) withObject:nil afterDelay:0];
         [[NSRunLoop currentRunLoop] runMode:NSDefaultRunLoopMode beforeDate:[NSDate distantFuture]];
     });
 }
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• 4.将[self performSelector:@selector(test) withObject:nil afterDelay:0]; 改为[self performSelector:@selector(test) withObject:nil];