iOS 同步异步多任务顺序执行

多任务按照顺序执行时(task1-->task2-->task3-->TaskSuccess)我们通常会用dispatch_group_async、dispatch_group_notify结合来完成或者使用栅栏,但这种操作只针对内部执行的任务是同步的

1. dispatch_group_async、dispatch_group_notify结合的方式

    dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
        
    dispatch_group_t group = dispatch_group_create();
        
        dispatch_group_async(group, queue, ^{
            NSLog(@"task1");
        });
        
        dispatch_group_async(group, queue, ^{
          NSLog(@"task2");
        });

        dispatch_group_async(group, queue, ^{

            NSLog(@"task3");
        });
    
    dispatch_group_notify(group, dispatch_get_main_queue(), ^{

        NSLog(@"TaskSuccess");
    });

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2. 栅栏方式

  dispatch_queue_t queue =dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT,0);
    
    dispatch_async(queue, ^{
        NSLog(@"task1");
    });
    
    dispatch_async(queue, ^{
        NSLog(@"task2");
    });
    
    dispatch_async(queue, ^{
        NSLog(@"task3");
    });
  
    dispatch_barrier_async(queue, ^{
           NSLog(@"TaskSuccess");
    });

image.png

对于任务中有异步的,可以使用采用dispatch_group_enter、dispatch_group_leave或者信号量实现

1. dispatch_group_enter、dispatch_group_leave结合的方式

 dispatch_group_t group = dispatch_group_create();
    
    dispatch_group_enter(group);
    [self loadData1:^{
        NSLog(@"task1");
        dispatch_group_leave(group);
    }];
    
    dispatch_group_enter(group);
    [self loadData2:^{
        NSLog(@"task2");
        dispatch_group_leave(group);
    }];
  
    dispatch_group_wait(group, DISPATCH_TIME_NOW);// task1 task2 执行完 下面才会执行
    
    dispatch_group_enter(group);
    [self loadData3:^{
        NSLog(@"task3");
        dispatch_group_leave(group);
    }];
    
    // 1 2 3 都完成 才会执行
    dispatch_group_notify(group, dispatch_get_global_queue(0, 0), ^{
        NSLog(@"taskSuccess!");
    });


//调用方法
-(void)loadData1:(nullable void (^)(void))block{
    
    NSDictionary *parDic = @{};
    [NetWorkRequest postNetRequestData:StaffRuleUrl parmeters:parDic response:^(NSDictionary *response) {
        if (response) {
            if ([response[@"stat"] isEqualToString:@"0"]) {
                block();
            }
        }
    } netError:^(NSError *error) {
    }];
}

-(void)loadData2:(nullable void (^)(void))block{
    
    NSDictionary *parDic = @{};
    [NetWorkRequest postNetRequestData:StaffRuleUrl parmeters:parDic response:^(NSDictionary *response) {
        if (response) {
            if ([response[@"stat"] isEqualToString:@"0"]) {
                block();
            }
        }
    } netError:^(NSError *error) {
    }];
}

-(void)loadData3:(nullable void (^)(void))block{
    
    NSDictionary *parDic = @{};
    [NetWorkRequest postNetRequestData:StaffRuleUrl parmeters:parDic response:^(NSDictionary *response) {
        if (response) {
            if ([response[@"stat"] isEqualToString:@"0"]) {
                block();
            }
        }
    } netError:^(NSError *error) {
    }];
}

image.png

先执行到dispatch_group_wait,然后才去执行上边的两个任务，由于enter数不等于leave数，进行等待，当task1、task2完成后调用dispatch_group_leave ，enter数等于leave数，才去执行请求3。 task1、task2、task3都执行后，dispatch_group_notify最后执行

2. 信号量方式

    dispatch_async(dispatch_get_global_queue(0, 0), ^{
        
        dispatch_semaphore_t semaphore = dispatch_semaphore_create(0);
        
        [self loadData1:^{
            NSLog(@"task1");
            dispatch_semaphore_signal(semaphore);
        }];
        
        dispatch_semaphore_wait(semaphore, DISPATCH_TIME_FOREVER);
        
        [self loadData2:^{
            NSLog(@"task2");
        }];
    });

image.png

执行到dispatch_semaphore_wait时，由于信号量为0，进行等待，请求1完成后调用dispatch_semaphore_signal ，信号量不再为0，接着执行请求2,signal wait成对出现

参照 : GCD控制