#import "ViewController.h"@interface ViewController ()@end@implementation ViewController- (void)viewDidLoad {[super viewDidLoad];#pragma mark -- GCD串行队列--//系统提过的一个串行队列//使用系统提供串行队列(主线程队列)
    dispatch_queue_t queue = dispatch_get_main_queue();//创建一个串行队列//第一个参数: 系统提供好的一个宏//第二个参数: 系统保留字段 0
    dispatch_queue_t queue = dispatch_queue_create(DISPATCH_QUEUE_SERIAL, 0);#pragma mark -- 创建一个并行的队列--//使用系统提供的并行队列//DISPATCH_QUEUE_PRIORITY_BACKGROUND表示队列的优先级// 0 保留字段
    dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_BACKGROUND, 0);//创建一个并行队列//第一个参数: 表示这个队列的名字//第二个参数: 表示系统提供好的一个宏// dispatch_queue_t queue = dispatch_queue_create("myQueue", DISPATCH_QUEUE_CONCURRENT);//使用dispatch_async 向队列中添加任务dispatch_async(queue, ^{NSLog(@"mian == %@, current == %@", [NSThread mainThread], [NSThread currentThread]);});dispatch_async(queue, ^{NSLog(@"mian1 == %@, current1 == %@", [NSThread mainThread], [NSThread currentThread]);});dispatch_async(queue, ^{NSLog(@"mian2 == %@, current2 == %@", [NSThread mainThread], [NSThread currentThread]);});dispatch_async(queue, ^{NSLog(@"mian3 == %@, current3 == %@", [NSThread mainThread], [NSThread currentThread]);});dispatch_async(queue, ^{NSLog(@"mian4 == %@, current4 == %@", [NSThread mainThread], [NSThread currentThread]);});#pragma mark  -- 表示几秒之后做什么事情--//    dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(3.0f * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
//        NSLog(@"已经3秒之后了");
//
//    });
//    #pragma mark -- 重复的向一个队列中添加一系列的任务--dispatch_queue_t queue = dispatch_queue_create(0, DISPATCH_QUEUE_SERIAL);dispatch_apply(3, queue, ^(size_t index) {NSLog(@"index == %zu", index);});#pragma mark -- 分组--//创建一个分组dispatch_group_t group = dispatch_group_create();//创建一个队列dispatch_queue_t queue = dispatch_queue_create("myQueue", DISPATCH_QUEUE_CONCURRENT);//向分组中添加一个任务dispatch_group_async(group, queue, ^{NSLog(@"我是第1个任务");});dispatch_group_async(group, queue, ^{NSLog(@"我是第2个任务");});dispatch_group_async(group, queue, ^{NSLog(@"我是第3个任务");});dispatch_group_async(group, queue, ^{NSLog(@"我是第4个任务");});//向分组添加结束任务//注意: 不要将结束任务放到第一个位置dispatch_group_notify(group, queue, ^{NSLog(@" 无论这样,我是最后一个任务");});#pragma  mark -- 并发中的串行 (披着羊皮的狼)--dispatch_queue_t queue = dispatch_queue_create("myQueue", DISPATCH_QUEUE_CONCURRENT);dispatch_async(queue, ^{NSLog(@"我是查询操作1");});dispatch_async(queue, ^{NSLog(@"我是查询操作2");});dispatch_barrier_async(queue, ^{NSLog(@"我是插入操作");});dispatch_async(queue, ^{NSLog(@"我是查询操作3");});dispatch_async(queue, ^{NSLog(@"我是查询操作4");});}

#import "MyObject.h"static MyObject *object = nil;@implementation MyObject+ (MyObject *)shareMyObject
{static dispatch_once_t onceToken;//表示同一时间内只有一个线程可以访问block块里面的内容
    dispatch_once(&onceToken, ^{if (object == nil) {object = [[MyObject alloc]init];}});return object;
}