并发队列，串队列，栅栏队列，组队列

更加深刻的去理解，并发队列，串队列，栅栏队列，组队列

对于barrier队列的同步和异步问题

//
//  ViewController.m
//  GCD DEV
//
//  Created by mac on 2017/2/21.
//  Copyright © 2017年 mac. All rights reserved.
//

#import "ViewController.h"

@interface ViewController ()

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.
    
    [self groupQueue];
    
}

/* 并发队列 **/
- (void)concurrentQueue {
    
    //并发
    dispatch_queue_t dispatch_queue = dispatch_queue_create("com.lee.dev", DISPATCH_QUEUE_CONCURRENT);
    dispatch_async(dispatch_queue, ^{
        
        sleep(1);
        NSLog(@"1");
    });
    dispatch_async(dispatch_queue, ^{
        
        sleep(2);
        NSLog(@"2");
    });
    
    /*
     *作用在 并发队列中 ，相当于一个栅栏，只有等这个栅栏的东西执行完了才往下走
     *但是注意的如果里面有一个 全局的异步线程
     **/
    dispatch_barrier_async(dispatch_queue, ^{
        
        sleep(3);
        NSLog(@"barrier");
        dispatch_async(dispatch_get_global_queue(0, 0), ^{
            
            sleep(3);
            NSLog(@"global_queue");
        });
    });
    
    dispatch_async(dispatch_queue, ^{
        NSLog(@"3");
    });
    dispatch_async(dispatch_queue, ^{
        NSLog(@"4");
    });
}

/* 同步队列 **/
- (void)serialQueue {
    
    //同步
    dispatch_queue_t dispatch_queue = dispatch_queue_create("com.lee.dev", DISPATCH_QUEUE_SERIAL);
    dispatch_async(dispatch_queue, ^{
        
        sleep(3);
        NSLog(@"同步：1");
    });
    dispatch_async(dispatch_queue, ^{
        
        sleep(2);
        NSLog(@"同步：2");
    });
    dispatch_async(dispatch_queue, ^{
        NSLog(@"同步：3");
    });
    dispatch_async(dispatch_queue, ^{
        NSLog(@"同步：4");
    });
}

/*
 * group 队列
 **/
- (void)groupQueue {
    
    NSArray *strings = @[@"http://img.wdjimg.com/image/video/d999011124c9ed55c2dd74e0ccee36ea_0_0.jpeg",
                         @"http://img.wdjimg.com/image/video/2ddcad6dcc38c5ca88614b7c5543199a_0_0.jpeg",
                         @"http://img.wdjimg.com/image/video/6d6ccfd79ee1deac2585150f40915c09_0_0.jpeg",
                         @"http://img.wdjimg.com/image/video/2111a863ea34825012b0c5c9dec71843_0_0.jpeg",
                         @"http://img.wdjimg.com/image/video/b4085a983cedd8a8b1e83ba2bd8ecdd8_0_0.jpeg",
                         @"http://img.wdjimg.com/image/video/2d59165e816151350a2b683b656a270a_0_0.jpeg",
                         @"http://img.wdjimg.com/image/video/dc2009ee59998039f795fbc7ac2f831f_0_0.jpeg"];
    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, ^{

        NSError * error = nil;
        NSData * data = [NSData dataWithContentsOfURL:[NSURL URLWithString:strings[0]] options:NSDataReadingMappedIfSafe error:&error];
        NSLog(@"NSThread_1:error:%@;length:%ld",error,data.length);
    });
    dispatch_group_async(group, queue, ^{
        
        NSError * error = nil;
        NSData * data = [NSData dataWithContentsOfURL:[NSURL URLWithString:strings[1]] options:NSDataReadingMappedIfSafe error:&error];
        NSLog(@"NSThread_2:error:%@;length:%ld",error,data.length);
    });
    dispatch_group_async(group, queue, ^{
        
        NSError * error = nil;
        NSData * data = [NSData dataWithContentsOfURL:[NSURL URLWithString:strings[2]] options:NSDataReadingMappedIfSafe error:&error];
        NSLog(@"NSThread_3:error:%@;length:%ld",error,data.length);
    });
    
    /* 通知**/
    dispatch_group_notify(group, dispatch_get_main_queue(), ^{
        
        NSLog(@"UI Op");
    });
}

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


@end