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原創(chuàng)文章，轉(zhuǎn)載請(qǐng)注明：轉(zhuǎn)自：Try_Try_Try
1.獲取Dispatch Queue 的兩種方法
- 方法一: 通過(guò)GCD api 生成隊(duì)列
dispatch_queue_create
// 串行隊(duì)列
dispatch_queue_t mySerialDispatchQueue = dispatch_queue_create("com.example.gcd.MySerialDispatchQueue", NULL);
dispatch_async(mySerialDispatchQueue, ^{
});
dispatch_release(mySerialDispatchQueue);
// 并行隊(duì)列
dispatch_queue_t myConcurrentDispatchQueue = dispatch_queue_create("com.example.gcd.MyConcurrentDispatchQueue", DISPATCH_QUEUE_CONCURRENT);
dispatch_async(myConcurrentDispatchQueue, ^{
NSLog(@"block on myConcurrentDispatchQueue");
});
dispatch_release(myConcurrentDispatchQueue);
- 方法二: 獲取系統(tǒng)標(biāo)準(zhǔn)提供的 Dispatch Queue
// 主隊(duì)列
dispatch_queue_t mainDispatchQueue = dispatch_get_main_queue();
// 全局并發(fā)隊(duì)列(4種優(yōu)先級(jí))
dispatch_queue_t globalDispatchQueueHeigh = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0);
dispatch_queue_t globalDispatchQueueDefault = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
dispatch_queue_t globalDispatchQueueLow = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_LOW, 0);
dispatch_queue_t globalDispatchQueueBackground = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_BACKGROUND, 0);
2.延時(shí)操作
- 3s后,將block追加到主隊(duì)列中進(jìn)行執(zhí)行;
dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(3 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
NSLog(@"waited at least 3 seconds");
});
3.隊(duì)列組
- 在一系列操作完成之后,再執(zhí)行其他內(nèi)容
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(@"blk0");
});
dispatch_group_async(group, queue, ^{
NSLog(@"blk1");
});
dispatch_group_async(group, queue, ^{
NSLog(@"blk2");
});
// 推薦
dispatch_group_notify(group, dispatch_get_main_queue(), ^{
NSLog(@"done");
});
// 不推薦
dispatch_time_t time = dispatch_time(DISPATCH_TIME_NOW, 1);
long result = dispatch_group_wait(group, time);
if (result == 0) { // group 的全部處理執(zhí)行結(jié)束
}else {
}
// dispatch_group_wait(group, DISPATCH_TIME_FOREVER);
dispatch_release(group);
4.柵欄函數(shù)
- 用于讀寫(xiě)操作引起的相關(guān)內(nèi)容;
- 每次的執(zhí)行結(jié)果可能不一樣,但是寫(xiě)操作一定會(huì)將0,1,2,3讀操作和4,5,6,7分隔開(kāi),從而達(dá)到不會(huì)誤讀的效果
dispatch_queue_t myConcurrentDispatchQueue = dispatch_queue_create("com.example.gcd.MyConcurrentDispatchQueue", DISPATCH_QUEUE_CONCURRENT);
__block NSInteger count = 1;
void (^blk0_for_reading)(void) = ^{NSLog(@"blk0_for_reading-%li%@", count, [NSThread currentThread]);};
void (^blk1_for_reading)(void) = ^{NSLog(@"blk1_for_reading-%li%@", count, [NSThread currentThread]);};
void (^blk2_for_reading)(void) = ^{NSLog(@"blk2_for_reading-%li%@", count,[NSThread currentThread]);};
void (^blk3_for_reading)(void) = ^{NSLog(@"blk3_for_reading-%li%@", count,[NSThread currentThread]);};
void (^blk4_for_writing)(void) = ^{ ++count; NSLog(@"---------blk4_for_writing-%li%@", count,[NSThread currentThread]);};
void (^blk5_for_reading)(void) = ^{NSLog(@"blk5_for_reading-%li%@", count,[NSThread currentThread]);};
void (^blk6_for_reading)(void) = ^{NSLog(@"blk6_for_reading-%li%@", count,[NSThread currentThread]);};
void (^blk7_for_reading)(void) = ^{NSLog(@"blk7_for_reading-%li%@", count,[NSThread currentThread]);};
void (^blk8_for_reading)(void) = ^{NSLog(@"blk8_for_reading-%li%@", count,[NSThread currentThread]);};
dispatch_async(myConcurrentDispatchQueue, blk0_for_reading);
dispatch_async(myConcurrentDispatchQueue, blk1_for_reading);
dispatch_async(myConcurrentDispatchQueue, blk2_for_reading);
dispatch_async(myConcurrentDispatchQueue, blk3_for_reading);
dispatch_barrier_async(myConcurrentDispatchQueue, blk4_for_writing);
dispatch_async(myConcurrentDispatchQueue, blk5_for_reading);
dispatch_async(myConcurrentDispatchQueue, blk6_for_reading);
dispatch_async(myConcurrentDispatchQueue, blk7_for_reading);
dispatch_async(myConcurrentDispatchQueue, blk8_for_reading);
// 結(jié)果
blk1_for_reading-1<NSThread: 0x170272e80>{number = 5, name = (null)}
2017-10-24 12:21:57.305030+0800 Test_copy_mutableCopy[1003:610433] blk0_for_reading-1<NSThread: 0x174073fc0>{number = 4, name = (null)}
2017-10-24 12:21:57.305121+0800 Test_copy_mutableCopy[1003:610433] blk3_for_reading-1<NSThread: 0x174073fc0>{number = 4, name = (null)}
2017-10-24 12:21:57.304973+0800 Test_copy_mutableCopy[1003:610435] blk2_for_reading-1<NSThread: 0x170272e80>{number = 5, name = (null)}
2017-10-24 12:21:57.305301+0800 Test_copy_mutableCopy[1003:610435] ---------blk4_for_writing-2<NSThread: 0x170272e80>{number = 5, name = (null)}
2017-10-24 12:21:57.305389+0800 Test_copy_mutableCopy[1003:610435] blk5_for_reading-2<NSThread: 0x170272e80>{number = 5, name = (null)}
2017-10-24 12:21:57.305460+0800 Test_copy_mutableCopy[1003:610435] blk6_for_reading-2<NSThread: 0x170272e80>{number = 5, name = (null)}
2017-10-24 12:21:57.305529+0800 Test_copy_mutableCopy[1003:610435] blk7_for_reading-2<NSThread: 0x170272e80>{number = 5, name = (null)}
2017-10-24 12:21:57.305598+0800 Test_copy_mutableCopy[1003:610433] blk8_for_reading-2<NSThread: 0x174073fc0>{number = 4, name = (null)}
5.死鎖的產(chǎn)生
必然引起死鎖的兩種方式
- 主隊(duì)列 + 同步函數(shù)
NSInteger count = 3; dispatch_queue_t mainQueue = dispatch_get_main_queue(); dispatch_sync(mainQueue, ^{NSLog(@"mainQueue-%li%@", count,[NSThread currentThread]);}); // result: 并沒(méi)有出現(xiàn)結(jié)果,因?yàn)橐呀?jīng)發(fā)生了死鎖 - 串行隊(duì)列 + 異步函數(shù)的block內(nèi)部是(該串行隊(duì)列 + 同步函數(shù))(
將串行隊(duì)列換成主隊(duì)列依然成立)dispatch_queue_t serialQueue = dispatch_queue_create("com.nextapp.qiannong", NULL); dispatch_async(serialQueue, ^{ dispatch_sync(serialQueue, ^{NSLog(@"no deadLock");}); }); // result: 并沒(méi)有出現(xiàn)結(jié)果,因?yàn)橐呀?jīng)發(fā)生了死鎖
6.dispatch_apply
dispatch_apply 與dispatch_sync 函數(shù)類(lèi)似(dispatch_group_async, dispatch_group_notify, dispatch_group_wait),會(huì)等待處理執(zhí)行結(jié)束,在向下執(zhí)行;
dispatch_group_async 沒(méi)有執(zhí)行次數(shù)的要求
dispatch_apply 必須有執(zhí)行的次數(shù)
-
dispatch_barrier_async ,用于前后都有讀取異步任務(wù),中間有一個(gè)寫(xiě)操作
// 建議在dispatch_async中異步執(zhí)行dispatch_apply函數(shù) dispatch_async(globalQueue, ^{ dispatch_apply(10, globalQueue, ^(size_t index) { NSLog(@"%li-%@", index,[NSThread currentThread]); }); dispatch_async(dispatch_get_main_queue(), ^{ // 執(zhí)行更新界面的操作 NSLog(@"Done-%@", [NSThread currentThread]); }); }); // 試驗(yàn)之后,并沒(méi)有生效 dispatch_suspend(globalQueue); // 掛起 dispatch_resume(globalQueue); // 恢復(fù)
7.信號(hào)量機(jī)制相關(guān)
- 相比串行隊(duì)列 和 柵欄函數(shù) ,力度更小;
dispatch_queue_t globalQueue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
// 保證可訪問(wèn)NSMutableArray類(lèi)對(duì)象的線程只能有1個(gè)
dispatch_semaphore_t semaphore = dispatch_semaphore_create(1);
NSMutableArray *array = [NSMutableArray array];
for (int idx = 0; idx < 10000; idx ++) {
dispatch_async(globalQueue, ^{
// 一直等到執(zhí)行semaphore的是計(jì)數(shù)值>=1.
// long result = dispatch_semaphore_wait(semaphore, DISPATCH_TIME_FOREVER);
// if (result == 0) {
// }else {
// }
[array addObject:[NSNumber numberWithInt:idx]];
// 執(zhí)行結(jié)束之后,釋放該鎖, 將dsemaphore的值 + 1;
dispatch_semaphore_signal(semaphore);
});
}
NSLog(@"%@", array);
dispatch_release(semaphore);
8.單例
- 在程序中,只執(zhí)行一次
// 之前的初始化操作
static BOOL initialized = NO;
if (initialized == NO) {
/*
* 初始化操作
*/
initialized = YES;
}
// 多線程環(huán)境下更加的安全
static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{
/*
* 初始化操作
*/
});
9.簡(jiǎn)記
線程
- dispatch_sync/async:同步/異步是否開(kāi)啟新線程
- 異步不阻塞當(dāng)前線程，同步阻塞當(dāng)前線程
- serial/concurrent queue：串行/并行決定開(kāi)啟線程的條數(shù)
死鎖
- 同步的在當(dāng)前隊(duì)列中(串行)中添加任務(wù)
- 主隊(duì)列也是串行隊(duì)列
- 相互阻塞構(gòu)成死鎖
信號(hào)量(semaphore)
- 信號(hào)量是同步的(同步會(huì)阻塞當(dāng)前線程)
- semaphore.create(p): p >= 0
- semaphore.wait(): p <= 0, 阻塞當(dāng)前線程， p -= 1
- semaphore.signal(): p += 1
group
- 實(shí)現(xiàn)多個(gè)網(wǎng)絡(luò)的異步請(qǐng)求，最后再同步執(zhí)行任務(wù)
- group.enter(), group.leave(), group.notify()
