iOS dispatch_set_target_queue 详解

dispatch_set_target_queue

有两个作用，1是修改队列的优先级

下面的实例代码就修改了队列的优先级，队列创建出来后，优先级都是默认的，可以通过

dispatch_set_target_queue来修改优先级。

2.让不同任务在同一个串行线程运行，下面演示了在并行线程运行的例子，表明在并行线程dispatch_set_target_queue 不能让任务按顺序执行

//
//  ViewController.m
//  test_dispatch_o1
//
//  Created by jeffasd on 16/7/13.
//  Copyright © 2016年 jeffasd. All rights reserved.
//

#import "ViewController.h"

@interface ViewController ()

@end

@implementation ViewController

- (void)viewDidLoad {
[super viewDidLoad];

}

- (void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event{

dispatch_queue_t targetQueue = dispatch_queue_create("test.target.queue", DISPATCH_QUEUE_SERIAL);

//    dispatch_queue_t targetQueue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0);

dispatch_queue_t queue1 = dispatch_queue_create("test.1", DISPATCH_QUEUE_SERIAL);
dispatch_queue_t queue2 = dispatch_queue_create("test.2", DISPATCH_QUEUE_SERIAL);
dispatch_queue_t queue3 = dispatch_queue_create("test.3", DISPATCH_QUEUE_SERIAL);

dispatch_set_target_queue(queue1, targetQueue);
dispatch_set_target_queue(queue2, targetQueue);
dispatch_set_target_queue(queue3, targetQueue);

dispatch_async(queue1, ^{
NSLog(@"1 in");
[NSThread sleepForTimeInterval:3.f];
NSLog(@"1 out");
});

dispatch_async(queue2, ^{
NSLog(@"2 in");
[NSThread sleepForTimeInterval:2.f];
NSLog(@"2 out");
});
dispatch_async(queue3, ^{
NSLog(@"3 in");
[NSThread sleepForTimeInterval:1.f];
NSLog(@"3 out");
});

}

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

@end