dispatch_after

dispatch_after延遲將任務(wù)提交到隊(duì)列中，注意不是事先將任務(wù)添加到隊(duì)列中然后再延遲執(zhí)行。

dispatch_queue_t serialQueue = dispatch_queue_create("serialQueue", DISPATCH_QUEUE_SERIAL);
dispatch_sync(serialQueue, ^{
        NSLog(@"任務(wù)1，%@", [NSThread currentThread]);
    });

dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(5*NSEC_PER_SEC)), serialQueue, ^{
        NSLog(@"5秒后提交該block,%@", [NSThread currentThread]);
    });
dispatch_sync(serialQueue, ^{
        NSLog(@"任務(wù)2，%@", [NSThread currentThread]);
    });
/**
dispatch_time_t
dispatch_time（）創(chuàng)建時(shí)間
DISPATCH_TIME_NOW從現(xiàn)在開始計(jì)算
NSEC_PER_SEC=1秒
*/
dispatch_time_t time = dispatch_time(DISPATCH_TIME_NOW, (int64_t)(2*NSEC_PER_SEC));
dispatch_after(time, serialQueue, ^{
        NSLog(@"2秒后提交該block，%@", [NSThread currentThread]);
    });

dispatch_after

從打印日志可以看出，所有任務(wù)都是添加到串行隊(duì)列中的，由串行隊(duì)列的特性可知：先進(jìn)入對(duì)的任務(wù)結(jié)束，才會(huì)執(zhí)行后面的任務(wù)，可驗(yàn)證dispatch_after是將任務(wù)延時(shí)添加到隊(duì)列中。

DISPATCH_TIME_NOW是指執(zhí)行到該行代碼時(shí)開始計(jì)算。

dispatch_queue_t serialQueue = dispatch_queue_create("serialQueue", DISPATCH_QUEUE_SERIAL);
dispatch_sync(serialQueue, ^{
        NSLog(@"任務(wù)1，%@", [NSThread currentThread]);
    });

dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(5*NSEC_PER_SEC)), serialQueue, ^{
        NSLog(@"5秒后提交該block,%@", [NSThread currentThread]);
    });
dispatch_sync(serialQueue, ^{
        NSLog(@"任務(wù)2，%@", [NSThread currentThread]);
        sleep(10);
    });
/**
dispatch_time_t
dispatch_time（）創(chuàng)建時(shí)間
DISPATCH_TIME_NOW從現(xiàn)在開始計(jì)算
NSEC_PER_SEC=1秒
*/
dispatch_time_t time = dispatch_time(DISPATCH_TIME_NOW, (int64_t)(2*NSEC_PER_SEC));
dispatch_after(time, serialQueue, ^{
        NSLog(@"2秒后提交該block，%@", [NSThread currentThread]);
    });

DISPATCH_TIME_NOW

從兩次的打印日志中也可以看出，dispatch_after是另外開辟了一條線程執(zhí)行的。

dispatch_group_t

dispatch_group_t：調(diào)度組，可以將隊(duì)列中的任務(wù)放到調(diào)度組中，由調(diào)度組來控制任務(wù)的執(zhí)行。

dispatch_queue_t concurrentQueue = dispatch_queue_create("concurrentQueue", DISPATCH_QUEUE_CONCURRENT);
dispatch_group_t group = dispatch_group_create();
dispatch_group_async(group, concurrentQueue, ^{
        NSLog(@"任務(wù)1%@", [NSThread currentThread]);
    });
dispatch_group_async(group, concurrentQueue, ^{
        NSLog(@"任務(wù)2%@", [NSThread currentThread]);
    });
dispatch_group_async(group, concurrentQueue, ^{
        NSLog(@"任務(wù)3%@", [NSThread currentThread]);
    });
dispatch_group_notify(group, concurrentQueue, ^{
        NSLog(@"調(diào)度組中concurrentQueue隊(duì)列的所有任務(wù)執(zhí)行完畢%@", [NSThread currentThread]);
    });

調(diào)度組1

• dispatch_group_async：創(chuàng)建一個(gè)異步任務(wù)將其放在concurrentQueue隊(duì)列中，并關(guān)聯(lián)到調(diào)度組中。
• dispatch_group_notify：concurrentQueue隊(duì)列中所有關(guān)聯(lián)到調(diào)度組中的任務(wù)結(jié)束時(shí)執(zhí)行。

dispatch_queue_t concurrentQueue = dispatch_queue_create("concurrentQueue", DISPATCH_QUEUE_CONCURRENT);
dispatch_group_enter(group);
dispatch_async(concurrentQueue, ^{
        NSLog(@"任務(wù)1%@", [NSThread currentThread]);
        dispatch_group_leave(group);
    });

dispatch_group_enter(group);
dispatch_async(concurrentQueue, ^{
        NSLog(@"任務(wù)2%@", [NSThread currentThread]);
        dispatch_group_leave(group);
    });
    
dispatch_group_enter(group);
dispatch_async(concurrentQueue, ^{
        NSLog(@"任務(wù)3%@", [NSThread currentThread]);
        dispatch_group_leave(group);
    });

調(diào)度組2

• dispatch_group_enter：任務(wù)入組。
• dispatch_group_leave：任務(wù)出組。

dispatch_group_enter和dispatch_group_leave需要成對(duì)出現(xiàn)。

dispatch_time_t time = dispatch_time(DISPATCH_TIME_NOW, (int64_t)(3*NSEC_PER_SEC));
dispatch_group_t group = dispatch_group_create();
dispatch_group_enter(group);
dispatch_async(concurrentQueue, ^{
        NSLog(@"任務(wù)1%@", [NSThread currentThread]);
        dispatch_group_leave(group);
    });

dispatch_group_enter(group);
dispatch_async(concurrentQueue, ^{
        NSLog(@"任務(wù)2%@", [NSThread currentThread]);
        dispatch_group_leave(group);
    });
    
dispatch_group_enter(group);
dispatch_async(concurrentQueue, ^{
        sleep(5);
        NSLog(@"任務(wù)3%@", [NSThread currentThread]);
        dispatch_group_leave(group);
    });

dispatch_group_notify(group, concurrentQueue, ^{
        NSLog(@"調(diào)度組中concurrentQueue隊(duì)列的所有任務(wù)執(zhí)行完畢%@", [NSThread currentThread]);
    });
dispatch_async(dispatch_get_global_queue(0, 0), ^{
        dispatch_group_wait(group, time);
        NSLog(@"頂多等你三秒，調(diào)度組不結(jié)束我就干自己的事去了");
    });

調(diào)度組3

dispatch_apply

dispatch_apply：重復(fù)提交任務(wù)到隊(duì)列中。

dispatch_apply(10, serialQueue, ^(size_t i) {
        NSLog(@"在線程中循環(huán)10次執(zhí)行該block%ld%@", i, [NSThread currentThread]);
    });

串行隊(duì)列重復(fù)提交

在當(dāng)前線程中執(zhí)行，不會(huì)開辟新的線程。

dispatch_apply(10, concurrentQueue, ^(size_t i) {
        NSLog(@"在線程中循環(huán)10次執(zhí)行該block%ld%@", i, [NSThread currentThread]);
    });

會(huì)開辟新的線程，異步執(zhí)行任務(wù)。

并行隊(duì)列重復(fù)提交

其他

• dispatch_queue_get_label：獲取隊(duì)列的名字。

//獲取指定隊(duì)列的名字
NSLog(@"%s", dispatch_queue_get_label(serialQueue));

//獲取當(dāng)前隊(duì)列的名字
NSLog(@"%s", dispatch_queue_get_label(DISPATCH_CURRENT_QUEUE_LABEL));