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本文內(nèi)容:
如何使用NSOperation創(chuàng)建任務(wù)、設(shè)置依賴、設(shè)置優(yōu)先級(jí)
如何使用NSOperationQueue創(chuàng)建隊(duì)列，添加任務(wù)到隊(duì)列、控制隊(duì)列串行、并行執(zhí)行任務(wù)
線程間如何通信
如何保證線程安全
iOS多線程demo地址

上文說(shuō)到iOS 多線程-GCD
這篇文章來(lái)講講NSOperation + NSOperationQueue

NSOperation：基于OC語(yǔ)言的API，底層是GCD，增加了一些簡(jiǎn)單易用的功能，面向?qū)ο蟛僮?，線程的生命周期系統(tǒng)自動(dòng)管理，在開(kāi)發(fā)中經(jīng)常使用。

1. NSOperation & NSOperationQueue

NSOperation：執(zhí)行的操作，也就是任務(wù)的意思，不過(guò)NSOperation：是一個(gè)抽象基類，不能直接使用。

NSOperation兩種使用方式：

使用系統(tǒng)定義的NSInvocationOperation
使用系統(tǒng)定義的NSBlockOperation
自定義類繼承NSOperation

任務(wù)的狀態(tài)分為以下幾種：

ready : 就緒
cancelled ：取消（只能取消沒(méi)有開(kāi)始的任務(wù)）
executing ：正在執(zhí)行
finished ：完成
asynchronous ：并發(fā)還是非并發(fā)

NSOperationQueue: 存放任務(wù)的隊(duì)列。
隊(duì)列分為：

主隊(duì)列：添加到主隊(duì)列的任務(wù)，只能在主線程執(zhí)行，除addExecutionBlock添加的額外任務(wù)，任務(wù)可能在其他線程執(zhí)行（下面有證明）；
其他隊(duì)列：添加到其他隊(duì)列的任務(wù)在子線程執(zhí)行。

常用方法：

NSOperation使用addDependency添加依賴，控制任務(wù)是否進(jìn)入就緒狀態(tài)，從而控制任務(wù)執(zhí)行順序。
NSOperationQueue使用addOperation添加任務(wù)到隊(duì)列。
NSOperationQueue設(shè)置 maxConcurrentOperationCount（最大操作并發(fā)數(shù)），用來(lái)控制一個(gè)隊(duì)列中有多少個(gè)任務(wù)同時(shí)進(jìn)行，而不是并發(fā)線程的數(shù)量。
NSOperation使用cancel 取消當(dāng)前任務(wù)
NSOperationQueue使用cancelAllOperations取消當(dāng)前隊(duì)列的任務(wù)
NSOperationQueue使用setSuspended設(shè)置任務(wù)的暫停和恢復(fù)

注意：

任務(wù)、隊(duì)列的取消并不代表可以將當(dāng)前的操作立即取消，而是當(dāng)前的操作執(zhí)行完畢之后不再執(zhí)行新的操作

暫停和取消的區(qū)別就在于：暫停操作之后還可以恢復(fù)操作，繼續(xù)向下執(zhí)行；而取消操作之后，所有的操作就清空了，無(wú)法再接著執(zhí)行剩下的操作。

2.使用步驟

創(chuàng)建任務(wù)
創(chuàng)建隊(duì)列
將任務(wù)添加到隊(duì)列中執(zhí)行

2.1創(chuàng)建任務(wù)

2.1.1 NSInvocationOperation

使用NSInvocationOperation創(chuàng)建任務(wù)，使用start方式開(kāi)始任務(wù)

- (void)clickNSOperation{
    NSLog(@"主線程");
    
//    1、NSInvocationOperation
    NSInvocationOperation *invocationOperation = [[NSInvocationOperation alloc]initWithTarget:self selector:@selector(invocationAction) object:nil];
    [invocationOperation start];
    NSLog(@"end----");
}
- (void)invocationAction{

    for (NSInteger index = 0; index < 3; index ++) {
        NSLog(@"invocation ==== %ld",(long)index);
        [NSThread sleepForTimeInterval:1.0];
    }
}

輸出結(jié)果：

在主線程中執(zhí)行（因?yàn)槭窃谥骶€程中調(diào)用）
end最后輸出，start方式執(zhí)行任務(wù)是同步執(zhí)行，睡眠時(shí)阻塞當(dāng)前線程。

2019-01-03 15:59:44.044995+0800 Thread[5045:65704] 主線程
2019-01-03 15:59:44.045577+0800 Thread[5045:65704] invocation ==== 0
2019-01-03 15:59:45.046159+0800 Thread[5045:65704] invocation ==== 1
2019-01-03 15:59:46.047736+0800 Thread[5045:65704] invocation ==== 2
2019-01-03 15:59:47.048575+0800 Thread[5045:65704] end----

在主線程調(diào)用就在主線程執(zhí)行，那在子線程中調(diào)用會(huì)如何呢？

- (void)clickNSOperation{
    NSLog(@"主線程");
    
    dispatch_async(dispatch_get_global_queue(0, 0), ^{
        //    1、NSInvocationOperation
        NSInvocationOperation *invocationOperation = [[NSInvocationOperation alloc]initWithTarget:self selector:@selector(invocationAction) object:nil];
        //start 是同步方式
        [invocationOperation start];
        NSLog(@"end----");
    });
}

輸出結(jié)果：

任務(wù)在子線程中執(zhí)行（因?yàn)槭亲又骶€程中調(diào)用）
end最后輸出，start方式執(zhí)行任務(wù)是同步執(zhí)行，睡眠時(shí)阻塞當(dāng)前線程。

2019-01-03 16:01:59.252994+0800 Thread[5075:66813] 主線程
2019-01-03 16:01:59.254415+0800 Thread[5075:66861] invocation ==== 0
2019-01-03 16:02:00.257107+0800 Thread[5075:66861] invocation ==== 1
2019-01-03 16:02:01.259739+0800 Thread[5075:66861] invocation ==== 2
2019-01-03 16:02:02.261961+0800 Thread[5075:66861] end----

由此可見(jiàn)，使用NSInvocationOperation + start方式執(zhí)行任務(wù)，在哪個(gè)線程調(diào)用，就在哪個(gè)線程執(zhí)行，執(zhí)行方式是同步執(zhí)行。

2.1.2NSBlockOperation

使用NSBlockOperation創(chuàng)建一個(gè)任務(wù)，并使用start方式開(kāi)始任務(wù)

- (void)clickNSOperation{
    NSLog(@"主線程");
    
NSBlockOperation *blockOperation = [NSBlockOperation blockOperationWithBlock:^{
        for (NSInteger index = 0; index < 3; index ++) {
            NSLog(@"1 ==== %ld",(long)index);
            [NSThread sleepForTimeInterval:1.0];
        }
    }];
     [blockOperation start];
     NSLog(@"end----");
}

輸出結(jié)果：

在主線程中執(zhí)行（因?yàn)槭窃谥骶€程中調(diào)用）
end最后輸出，start方式執(zhí)行任務(wù)是同步執(zhí)行，睡眠時(shí)阻塞當(dāng)前線程。

2019-01-03 16:41:28.661599+0800 Thread[5506:85345] 主線程
2019-01-03 16:41:28.662055+0800 Thread[5506:85345] 1 ==== 0
2019-01-03 16:41:29.663436+0800 Thread[5506:85345] 1 ==== 1
2019-01-03 16:41:30.664878+0800 Thread[5506:85345] 1 ==== 2
2019-01-03 16:41:31.666310+0800 Thread[5506:85345] end----

執(zhí)行一個(gè)任務(wù)時(shí)，省略在子線程調(diào)用start執(zhí)行任務(wù)，因?yàn)榻Y(jié)果和NSInvocationOperation一樣在哪個(gè)線程調(diào)用，就在哪個(gè)線程同步執(zhí)行。

NSBlockOperation還有一個(gè)方法addExecutionBlock用來(lái)添加額外任務(wù)，可用于執(zhí)行多個(gè)任務(wù)，比如說(shuō)想同時(shí)執(zhí)行2個(gè)任務(wù)。

- (void)clickNSOperation{
    NSLog(@"主線程");
    NSBlockOperation *blockOperation = [NSBlockOperation blockOperationWithBlock:^{
        for (NSInteger index = 0; index < 3; index ++) {
            NSLog(@"1 ==== %ld",(long)index);
            [NSThread sleepForTimeInterval:1.0];
        }
    }];
    [blockOperation addExecutionBlock:^{
        for (NSInteger index = 0; index < 3; index ++) {
            NSLog(@"2 ==== %ld",(long)index);
            [NSThread sleepForTimeInterval:1.0];
        }
    }];

    [blockOperation start];
    NSLog(@"end----");

}

輸出結(jié)果：

任務(wù)1在主線程執(zhí)行，任務(wù)2在子線程執(zhí)行。由此證明，addExecutionBlock添加的任務(wù)，可能在其他子線程執(zhí)行。
end最后輸出，start方式執(zhí)行任務(wù)是同步執(zhí)行，睡眠時(shí)阻塞當(dāng)前線程。

2019-01-03 16:47:02.219309+0800 Thread[5552:87869] 主線程
2019-01-03 16:47:02.219847+0800 Thread[5552:87896] 1 ==== 0
2019-01-03 16:47:02.219870+0800 Thread[5552:87869] 2 ==== 0
2019-01-03 16:47:03.221204+0800 Thread[5552:87896] 1 ==== 1
2019-01-03 16:47:03.221214+0800 Thread[5552:87869] 2 ==== 1
2019-01-03 16:47:04.222522+0800 Thread[5552:87896] 1 ==== 2
2019-01-03 16:47:04.222522+0800 Thread[5552:87869] 2 ==== 2
2019-01-03 16:47:05.223986+0800 Thread[5552:87869] end----

使用addExecutionBlock方式執(zhí)行多個(gè)任務(wù)時(shí)，會(huì)開(kāi)啟線程，具體開(kāi)啟幾個(gè)線程是由系統(tǒng)決定的。

2.1.3 自定義類繼承NSOperation

創(chuàng)建一個(gè)類繼承自NSOperation，這里創(chuàng)建的是XXOperation

#import "XXOperation.h"

@interface XXOperation ()
@property (nonatomic , copy) NSString *operName;
@property (nonatomic , assign) BOOL over;

@end

@implementation XXOperation

- (instancetype)initWithName:(NSString *)operName{
    if (self = [super init]) {
        self.operName = operName;
    }
    return self;
}

- (void)main{
    for (NSInteger index = 0; index < 3; index ++) {
        NSLog(@"index ==== %d,operName = %@",index,self.operName);
        [NSThread sleepForTimeInterval:1.0];
    }
  }

使用start方式調(diào)用

- (void)clickNSOperation{
    NSLog(@"主線程");
    XXOperation *operationA = [[XXOperation alloc]initWithName:@"operationA"];
    [operationA start];
  NSLog(@"end---");
}

輸出結(jié)果：

在主線程中執(zhí)行（因?yàn)槭窃谥骶€程中調(diào)用）
end最后輸出，start方式執(zhí)行任務(wù)是同步執(zhí)行，睡眠時(shí)阻塞當(dāng)前線程。

2019-01-03 16:20:16.400576+0800 Thread[5270:75970] 主線程
2019-01-03 16:20:16.401009+0800 Thread[5270:75970] index ==== 0,operName = operationA
2019-01-03 16:20:17.401740+0800 Thread[5270:75970] index ==== 1,operName = operationA
2019-01-03 16:20:18.402675+0800 Thread[5270:75970] index ==== 2,operName = operationA
2019-01-03 16:20:19.404857+0800 Thread[5270:75970] end---

自定義類繼承NSOperation在子線程中調(diào)用任務(wù)，這里就省略了，
因?yàn)榻Y(jié)果和NSInvocationOperation、NSBlockOperation執(zhí)行一個(gè)任務(wù)時(shí)一樣，在哪個(gè)線程調(diào)用，就在哪個(gè)線程同步執(zhí)行任務(wù)。

但是我們常見(jiàn)的需求中是異步并發(fā)執(zhí)行，如何實(shí)現(xiàn)異步并發(fā)執(zhí)行呢？我們需要使用NSOperation + NSOperationQueue實(shí)現(xiàn)異步并發(fā)。

隊(duì)列又分為兩種，添加到主隊(duì)列的任務(wù)，只能在主線程執(zhí)行，除addExecutionBlock添加的額外任務(wù)，可能在其他線程執(zhí)行。添加到其他隊(duì)列的任務(wù)在子線程執(zhí)行。

由此可見(jiàn)，使用 NSOperation + 其他隊(duì)列是較佳方法，既不阻塞主線程，又能執(zhí)行其他任務(wù)。

2.2創(chuàng)建隊(duì)列

2.2.1主隊(duì)列

//獲取主隊(duì)列
   NSOperationQueue *queue = [NSOperationQueue mainQueue];

2.2.2其他隊(duì)列

NSOperationQueue *queue = [[NSOperationQueue alloc]init];

3.添加任務(wù)到隊(duì)列

addOperation:(NSOperation *)op: 直接添加一個(gè) NSOperation操作
addOperations:(NSArray<NSOperation *> *)ops waitUntilFinished:(BOOL)wait : 添加一組操作,wait標(biāo)志是否阻塞當(dāng)前線程直到所有操作結(jié)束
addOperationWithBlock:(void (^)(void))block:將block中的操作加入隊(duì)列

這里使用addOperation方式添加任務(wù)到隊(duì)列，并且不設(shè)置maxConcurrentOperationCount

- (void)clickNSOperation{
    XXOperation *operationA = [[XXOperation alloc]initWithName:@"operationA"];
    XXOperation *operationB = [[XXOperation alloc]initWithName:@"operationB"];
    XXOperation *operationC = [[XXOperation alloc]initWithName:@"operationC"];
    XXOperation *operationD = [[XXOperation alloc]initWithName:@"operationD"];
    if (!self.operationQueue) {
        self.operationQueue = [[NSOperationQueue alloc]init];
    }
    [self.operationQueue addOperation:operationA];
    [self.operationQueue addOperation:operationB];
    [self.operationQueue addOperation:operationC];
    [self.operationQueue addOperation:operationD];
    
}

輸出結(jié)果：

在多個(gè)子線程中執(zhí)行，并發(fā)執(zhí)行；
end在任務(wù)之前輸出，異步執(zhí)行。

2019-01-03 17:58:51.841334+0800 Thread[6257:118424] 主線程
2019-01-03 17:58:51.841926+0800 Thread[6257:118424] end---
2019-01-03 17:58:51.841962+0800 Thread[6257:118471] index ==== 0,operName = operationC
2019-01-03 17:58:51.841962+0800 Thread[6257:118472] index ==== 0,operName = operationD
2019-01-03 17:58:51.841963+0800 Thread[6257:118473] index ==== 0,operName = operationB
2019-01-03 17:58:51.841975+0800 Thread[6257:118474] index ==== 0,operName = operationA
2019-01-03 17:58:52.847300+0800 Thread[6257:118471] index ==== 1,operName = operationC
2019-01-03 17:58:52.847303+0800 Thread[6257:118472] index ==== 1,operName = operationD
2019-01-03 17:58:52.847300+0800 Thread[6257:118473] index ==== 1,operName = operationB
2019-01-03 17:58:52.847303+0800 Thread[6257:118474] index ==== 1,operName = operationA
2019-01-03 17:58:53.848148+0800 Thread[6257:118473] index ==== 2,operName = operationB
2019-01-03 17:58:53.848148+0800 Thread[6257:118474] index ==== 2,operName = operationA
2019-01-03 17:58:53.848148+0800 Thread[6257:118472] index ==== 2,operName = operationD
2019-01-03 17:58:53.848173+0800 Thread[6257:118471] index ==== 2,operName = operationC

4.控制串行、并行

NSOperationQueue通過(guò)設(shè)置maxConcurrentOperationCount來(lái)實(shí)現(xiàn)任務(wù)是串行還是并行。
maxConcurrentOperationCount: 最大操作并發(fā)數(shù)，用來(lái)控制一個(gè)隊(duì)列中有多少個(gè)任務(wù)同時(shí)進(jìn)行，而不是并發(fā)線程的數(shù)量。

在NSOperation.h里面，可以看見(jiàn) maxConcurrentOperationCount默認(rèn)值為-1

static const NSInteger NSOperationQueueDefaultMaxConcurrentOperationCount = -1;

maxConcurrentOperationCount默認(rèn)值為-1，不進(jìn)行限制，可以并行執(zhí)行;
maxConcurrentOperationCount = 1為串行隊(duì)列，只能串行執(zhí)行；
maxConcurrentOperationCount > 1為并行隊(duì)列，可以并行執(zhí)行，但是設(shè)置的值不能超過(guò)系統(tǒng)限制的最大值，如果超過(guò)系統(tǒng)限制的最大值，設(shè)置的值 = 系統(tǒng)限制的最大值；

此時(shí)將maxConcurrentOperationCount 設(shè)置為1

- (void)clickNSOperation{
    NSLog(@"主線程");
    XXOperation *operationA = [[XXOperation alloc]initWithName:@"operationA"];
    XXOperation *operationB = [[XXOperation alloc]initWithName:@"operationB"];
    XXOperation *operationC = [[XXOperation alloc]initWithName:@"operationC"];
    XXOperation *operationD = [[XXOperation alloc]initWithName:@"operationD"];
    if (!self.operationQueue) {
        self.operationQueue = [[NSOperationQueue alloc]init];
    }
    self.operationQueue.maxConcurrentOperationCount = 1;//值 = 1，串行隊(duì)列，
    [self.operationQueue addOperation:operationA];
    [self.operationQueue addOperation:operationB];
    [self.operationQueue addOperation:operationC];
    [self.operationQueue addOperation:operationD];
    NSLog(@"end---");
}

輸出結(jié)果：

end在任務(wù)之前輸出，異步執(zhí)行；
任務(wù)在多個(gè)子線程中執(zhí)行；
任務(wù)一個(gè)接著一個(gè)串行執(zhí)行，最后呈現(xiàn)結(jié)果就是異步串行。

由此證明：maxConcurrentOperationCount，用來(lái)控制一個(gè)隊(duì)列中有多少個(gè)任務(wù)同時(shí)進(jìn)行，而不是并發(fā)線程的數(shù)量。

2019-01-03 18:14:37.042902+0800 Thread[6370:123969] 主線程
2019-01-03 18:14:37.043486+0800 Thread[6370:123969] end---
2019-01-03 18:14:37.043535+0800 Thread[6370:124020] index ==== 0,operName = operationA
2019-01-03 18:14:38.043839+0800 Thread[6370:124020] index ==== 1,operName = operationA
2019-01-03 18:14:39.049215+0800 Thread[6370:124020] index ==== 2,operName = operationA
2019-01-03 18:14:40.054252+0800 Thread[6370:124021] index ==== 0,operName = operationB
2019-01-03 18:14:41.059064+0800 Thread[6370:124021] index ==== 1,operName = operationB
2019-01-03 18:14:42.061843+0800 Thread[6370:124021] index ==== 2,operName = operationB
2019-01-03 18:14:43.067389+0800 Thread[6370:124021] index ==== 0,operName = operationC
2019-01-03 18:14:44.072883+0800 Thread[6370:124021] index ==== 1,operName = operationC
2019-01-03 18:14:45.074068+0800 Thread[6370:124021] index ==== 2,operName = operationC
2019-01-03 18:14:46.076217+0800 Thread[6370:124020] index ==== 0,operName = operationD
2019-01-03 18:14:47.079396+0800 Thread[6370:124020] index ==== 1,operName = operationD
2019-01-03 18:14:48.084846+0800 Thread[6370:124020] index ==== 2,operName = operationD

將最大并發(fā)數(shù)設(shè)置為4

self.operationQueue.maxConcurrentOperationCount = 4;//值 = 4，并行隊(duì)列

輸出結(jié)果：

end在任務(wù)之前輸出，異步執(zhí)行；
任務(wù)在多個(gè)子線程中執(zhí)行；
任務(wù)并發(fā)執(zhí)行，最后呈現(xiàn)結(jié)果就是實(shí)現(xiàn)異步并發(fā)執(zhí)行（最完美狀態(tài)）

2019-01-03 18:19:58.120798+0800 Thread[6424:126327] 主線程
2019-01-03 18:19:58.121325+0800 Thread[6424:126327] end---
2019-01-03 18:19:58.121362+0800 Thread[6424:126374] index ==== 0,operName = operationB
2019-01-03 18:19:58.121339+0800 Thread[6424:126371] index ==== 0,operName = operationA
2019-01-03 18:19:58.121362+0800 Thread[6424:126373] index ==== 0,operName = operationD
2019-01-03 18:19:58.121371+0800 Thread[6424:126372] index ==== 0,operName = operationC
2019-01-03 18:19:59.122232+0800 Thread[6424:126372] index ==== 1,operName = operationC
2019-01-03 18:19:59.122231+0800 Thread[6424:126371] index ==== 1,operName = operationA
2019-01-03 18:19:59.122287+0800 Thread[6424:126373] index ==== 1,operName = operationD
2019-01-03 18:19:59.122231+0800 Thread[6424:126374] index ==== 1,operName = operationB
2019-01-03 18:20:00.127789+0800 Thread[6424:126371] index ==== 2,operName = operationA
2019-01-03 18:20:00.127789+0800 Thread[6424:126374] index ==== 2,operName = operationB
2019-01-03 18:20:00.127791+0800 Thread[6424:126372] index ==== 2,operName = operationC
2019-01-03 18:20:00.127791+0800 Thread[6424:126373] index ==== 2,operName = operationD

5. 操作依賴

操作依賴：控制任務(wù)是否進(jìn)入就緒狀態(tài)，從而控制任務(wù)執(zhí)行順序

- (void)addDependency:(NSOperation *)op;：添加依賴
(void)removeDependency:(NSOperation *)op ：刪除依賴
@property (readonly, copy) NSArray<NSOperation *> *dependencies：返回當(dāng)前依賴數(shù)組

上一個(gè)例子中，有4個(gè)任務(wù)，分別是A、B、C、D ，設(shè)置D依賴于A ，A 依賴于C，C 依賴于B，千萬(wàn)不能再設(shè)置B依賴于D，不然就是死循環(huán)了。

- (void)clickNSOperation{
    NSLog(@"主線程");
    XXOperation *operationA = [[XXOperation alloc]initWithName:@"operationA"];
    XXOperation *operationB = [[XXOperation alloc]initWithName:@"operationB"];
    XXOperation *operationC = [[XXOperation alloc]initWithName:@"operationC"];
    XXOperation *operationD = [[XXOperation alloc]initWithName:@"operationD"];
    if (!self.operationQueue) {
        self.operationQueue = [[NSOperationQueue alloc]init];
    }
//    self.operationQueue.maxConcurrentOperationCount = 1;//值 = 1，串行隊(duì)列
    self.operationQueue.maxConcurrentOperationCount = 4;//值 = 4，并行隊(duì)列

    // 設(shè)置D依賴于A ，A 依賴于C，C 依賴于B
    [operationD addDependency:operationA];
    [operationA addDependency:operationC];
    [operationC addDependency:operationB];
    
    [self.operationQueue addOperation:operationA];
    [self.operationQueue addOperation:operationB];
    [self.operationQueue addOperation:operationC];
    [self.operationQueue addOperation:operationD];
     NSLog(@"end---");
}

輸出結(jié)果：

end在任務(wù)之前輸出，異步執(zhí)行；
任務(wù)執(zhí)行順序B、C、A、D。
本來(lái)添加到隊(duì)列的任務(wù)順序是A、B、C、D，執(zhí)行A時(shí)，A依賴于C，C還未執(zhí)行結(jié)束，A處于未就緒狀態(tài)，只有等C執(zhí)行結(jié)束后，A才能處于就緒狀態(tài)，才能執(zhí)行任務(wù)。B沒(méi)有依賴，直接執(zhí)行，同理C依賴于B，，D依賴于A，所以執(zhí)行順序是B、C、A、D

2019-01-04 16:36:29.830947+0800 Thread[19747:188253] 主線程
2019-01-04 16:36:29.831568+0800 Thread[19747:188253] end---
2019-01-04 16:36:29.831603+0800 Thread[19747:188290] index ==== 0,operName = operationB
2019-01-04 16:36:30.832856+0800 Thread[19747:188290] index ==== 1,operName = operationB
2019-01-04 16:36:31.837187+0800 Thread[19747:188290] index ==== 2,operName = operationB
2019-01-04 16:36:32.842000+0800 Thread[19747:188289] index ==== 0,operName = operationC
2019-01-04 16:36:33.846089+0800 Thread[19747:188289] index ==== 1,operName = operationC
2019-01-04 16:36:34.851604+0800 Thread[19747:188289] index ==== 2,operName = operationC
2019-01-04 16:36:35.856626+0800 Thread[19747:188290] index ==== 0,operName = operationA
2019-01-04 16:36:36.859237+0800 Thread[19747:188290] index ==== 1,operName = operationA
2019-01-04 16:36:37.862654+0800 Thread[19747:188290] index ==== 2,operName = operationA
2019-01-04 16:36:38.866634+0800 Thread[19747:188289] index ==== 0,operName = operationD
2019-01-04 16:36:39.870859+0800 Thread[19747:188289] index ==== 1,operName = operationD
2019-01-04 16:36:40.873716+0800 Thread[19747:188289] index ==== 2,operName = operationD

6.優(yōu)先級(jí)

queuePriority，設(shè)置隊(duì)列中的任務(wù)的優(yōu)先級(jí)，目的是：控制進(jìn)入就緒狀態(tài)的任務(wù)的執(zhí)行順序。

沒(méi)有設(shè)置優(yōu)先級(jí)默認(rèn)是NSOperationQueuePriorityNormal，幾個(gè)優(yōu)先級(jí)有以下幾個(gè)選項(xiàng)：

typedef NS_ENUM(NSInteger, NSOperationQueuePriority) {
    NSOperationQueuePriorityVeryLow = -8L,
    NSOperationQueuePriorityLow = -4L,
    NSOperationQueuePriorityNormal = 0,
    NSOperationQueuePriorityHigh = 4,
    NSOperationQueuePriorityVeryHigh = 8
};

什么樣的任務(wù)處于就緒狀態(tài)呢？

添加到隊(duì)列中，并且依賴關(guān)系都已經(jīng)滿足，比如上面A依賴于C，C還未執(zhí)行結(jié)束，A就處于未就緒狀態(tài)，C執(zhí)行結(jié)束后，A才處于就緒狀態(tài)。

以下幾種條件，都是在maxConcurrentOperationCount = 1的情況下，剔除并發(fā)引起的問(wèn)題。

如果隊(duì)列中的任務(wù)都處于就緒狀態(tài)下，并且都沒(méi)有設(shè)置優(yōu)先級(jí)，都是默認(rèn)優(yōu)先級(jí)的時(shí)候，任務(wù)的執(zhí)行順序，就是先添加到隊(duì)列里面的任務(wù)先執(zhí)行。（控制串行、并行的第一個(gè)例子可以證明）
如果隊(duì)列中的任務(wù)都處于就緒狀態(tài)下，并且設(shè)置優(yōu)先級(jí)的時(shí)候，任務(wù)的執(zhí)行順序，就是優(yōu)先級(jí)越高的任務(wù)先執(zhí)行。
如果隊(duì)列中的任務(wù)有處于就緒狀態(tài)的，有未處于就緒狀態(tài)的，就緒狀態(tài)的優(yōu)先級(jí)低，未就緒狀態(tài)的優(yōu)先級(jí)高，此時(shí)還是執(zhí)行就緒狀態(tài)優(yōu)先級(jí)低的操作，因?yàn)橐蕾囮P(guān)系控制任務(wù)是否進(jìn)入就緒狀態(tài)，從而控制任務(wù)執(zhí)行順序，而優(yōu)先級(jí)則是控制進(jìn)入就緒狀態(tài)任務(wù)的執(zhí)行順序。

情況2的實(shí)現(xiàn)代碼

- (void)clickNSOperation{
    NSLog(@"主線程");
    XXOperation *operationA = [[XXOperation alloc]initWithName:@"operationA"];
    XXOperation *operationB = [[XXOperation alloc]initWithName:@"operationB"];
    XXOperation *operationC = [[XXOperation alloc]initWithName:@"operationC"];
    XXOperation *operationD = [[XXOperation alloc]initWithName:@"operationD"];
    if (!self.operationQueue) {
        self.operationQueue = [[NSOperationQueue alloc]init];
    }
   self.operationQueue.maxConcurrentOperationCount = 1;//值 = 1，串行隊(duì)列
//    self.operationQueue.maxConcurrentOperationCount = 4;//值 = 4，并行隊(duì)列
   //設(shè)置優(yōu)先級(jí)
    operationA.queuePriority = NSOperationQueuePriorityVeryHigh;
    operationB.queuePriority = NSOperationQueuePriorityVeryHigh;
    operationC.queuePriority = NSOperationQueuePriorityHigh;
    operationD.queuePriority = NSOperationQueuePriorityVeryHigh;
    [self.operationQueue addOperation:operationA];
    [self.operationQueue addOperation:operationB];
    [self.operationQueue addOperation:operationC];
    [self.operationQueue addOperation:operationD];
     NSLog(@"end---");

輸出結(jié)果：任務(wù)執(zhí)行順序A、B、D、C，跟任務(wù)優(yōu)先級(jí)關(guān)系成正比，優(yōu)先級(jí)越高，越先執(zhí)行，C優(yōu)先級(jí)比D低，所以D先執(zhí)行。

2019-01-07 10:58:02.635752+0800 Thread[1130:25079] index ==== 0,operName = operationA
2019-01-07 10:58:03.641122+0800 Thread[1130:25079] index ==== 1,operName = operationA
2019-01-07 10:58:04.645798+0800 Thread[1130:25079] index ==== 2,operName = operationA
2019-01-07 10:58:05.651342+0800 Thread[1130:25076] index ==== 0,operName = operationB
2019-01-07 10:58:06.651660+0800 Thread[1130:25076] index ==== 1,operName = operationB
2019-01-07 10:58:07.656731+0800 Thread[1130:25076] index ==== 2,operName = operationB
2019-01-07 10:58:08.661404+0800 Thread[1130:25079] index ==== 0,operName = operationD
2019-01-07 10:58:09.666161+0800 Thread[1130:25079] index ==== 1,operName = operationD
2019-01-07 10:58:10.668855+0800 Thread[1130:25079] index ==== 2,operName = operationD
2019-01-07 10:58:11.672342+0800 Thread[1130:25076] index ==== 0,operName = operationC
2019-01-07 10:58:12.676247+0800 Thread[1130:25076] index ==== 1,operName = operationC
2019-01-07 10:58:13.677245+0800 Thread[1130:25076] index ==== 2,operName = operationC

情況3的實(shí)現(xiàn)代碼

- (void)clickNSOperation{
    NSLog(@"主線程");
    XXOperation *operationA = [[XXOperation alloc]initWithName:@"operationA"];
    XXOperation *operationB = [[XXOperation alloc]initWithName:@"operationB"];
    XXOperation *operationC = [[XXOperation alloc]initWithName:@"operationC"];
    XXOperation *operationD = [[XXOperation alloc]initWithName:@"operationD"];
    if (!self.operationQueue) {
        self.operationQueue = [[NSOperationQueue alloc]init];
    }
   self.operationQueue.maxConcurrentOperationCount = 1;//值 = 1，串行隊(duì)列
//    self.operationQueue.maxConcurrentOperationCount = 4;//值 = 4，并行隊(duì)列
     // 設(shè)置D依賴于A ，A 依賴于C，C 依賴于B
    [operationD addDependency:operationA];
    [operationA addDependency:operationC];
    [operationC addDependency:operationB];
     //設(shè)置優(yōu)先級(jí)
    operationA.queuePriority = NSOperationQueuePriorityVeryHigh;
    operationB.queuePriority = NSOperationQueuePriorityVeryHigh;
    operationC.queuePriority = NSOperationQueuePriorityHigh;
    operationD.queuePriority = NSOperationQueuePriorityVeryHigh;

    [self.operationQueue addOperation:operationA];
    [self.operationQueue addOperation:operationB];
    [self.operationQueue addOperation:operationC];
    [self.operationQueue addOperation:operationD];
     NSLog(@"end---");

輸出結(jié)果：
如果只設(shè)置依賴關(guān)系，不設(shè)置優(yōu)先級(jí)，執(zhí)行順序是B、C、A、D
如果不設(shè)置依賴關(guān)系，只設(shè)置優(yōu)先級(jí)，執(zhí)行順序是A、B、D、C
同時(shí)設(shè)置依賴關(guān)系和優(yōu)先級(jí)，執(zhí)行順序依舊是B、C、A、D，因?yàn)橐蕾囮P(guān)系控制任務(wù)是否進(jìn)入就緒狀態(tài)，從而控制任務(wù)執(zhí)行順序，而優(yōu)先級(jí)則是控制進(jìn)入就緒狀態(tài)任務(wù)的執(zhí)行順序。因?yàn)镈依賴于A ，A 依賴于C，C 依賴于B，所以此時(shí)就緒狀態(tài)決定執(zhí)行順序。

2019-01-07 11:18:25.281981+0800 Thread[1162:31573] 主線程
2019-01-07 11:18:25.282591+0800 Thread[1162:31573] end---
2019-01-07 11:18:25.282638+0800 Thread[1162:31615] index ==== 0,operName = operationB
2019-01-07 11:18:26.287156+0800 Thread[1162:31615] index ==== 1,operName = operationB
2019-01-07 11:18:27.292264+0800 Thread[1162:31615] index ==== 2,operName = operationB
2019-01-07 11:18:28.297512+0800 Thread[1162:31615] index ==== 0,operName = operationC
2019-01-07 11:18:29.301186+0800 Thread[1162:31615] index ==== 1,operName = operationC
2019-01-07 11:18:30.302530+0800 Thread[1162:31615] index ==== 2,operName = operationC
2019-01-07 11:18:31.304189+0800 Thread[1162:31615] index ==== 0,operName = operationA
2019-01-07 11:18:32.304707+0800 Thread[1162:31615] index ==== 1,operName = operationA
2019-01-07 11:18:33.308931+0800 Thread[1162:31615] index ==== 2,operName = operationA
2019-01-07 11:18:34.309684+0800 Thread[1162:31615] index ==== 0,operName = operationD
2019-01-07 11:18:35.313671+0800 Thread[1162:31615] index ==== 1,operName = operationD
2019-01-07 11:18:36.317910+0800 Thread[1162:31615] index ==== 2,operName = operationD

7.線程間的通信

在iOS開(kāi)發(fā)工程中，我們一般在主線程中進(jìn)行UI刷新，如：點(diǎn)擊、拖拽、滾動(dòng)事件，耗時(shí)操作放在其他線程中，而當(dāng)耗時(shí)操作結(jié)束后，回到主線程，就需要用到線程間的通信

- (void)clickNSOperation{
    NSLog(@"主線程");
    self.operationQueue = [[NSOperationQueue alloc]init];
    [self.operationQueue addOperationWithBlock:^{
        for (NSInteger index = 0; index < 3; index ++) {
            NSLog(@"invocation ==== %ld",(long)index);
            [NSThread sleepForTimeInterval:1.0];
        }
        [[NSOperationQueue mainQueue] addOperationWithBlock:^{
            NSLog(@"回到主線程");
            NSLog(@"end---");
        }];
    }];
}

輸出結(jié)果：完成耗時(shí)操作后，回到了主線程

2019-01-07 13:59:09.784407+0800 Thread[1449:46686] 主線程
2019-01-07 13:59:09.785071+0800 Thread[1449:46730] invocation ==== 0
2019-01-07 13:59:10.789103+0800 Thread[1449:46730] invocation ==== 1
2019-01-07 13:59:11.793907+0800 Thread[1449:46730] invocation ==== 2
2019-01-07 13:59:12.796989+0800 Thread[1449:46686] 回到主線程
2019-01-07 13:59:12.797208+0800 Thread[1449:46686] end---

8.線程安全與線程同步

線程安全：在多個(gè)線程中同時(shí)訪問(wèn)并操作同一對(duì)象，運(yùn)行結(jié)果與預(yù)期的值相同就是線程安全。線程安全問(wèn)題都是由全局變量及靜態(tài)變量引起的，若每個(gè)線程中對(duì)全局變量、靜態(tài)變量只有讀操作，而無(wú)寫操作，一般來(lái)說(shuō)，這個(gè)全局變量是線程安全的；若有多個(gè)線程同時(shí)執(zhí)行寫操作，一般都需要考慮線程同步，否則的話就可能影響線程安全。

線程同步：可理解為線程A和B一塊配合，A執(zhí)行到一定程度時(shí)要依靠B的某個(gè)結(jié)果，于是停下來(lái)，示意B運(yùn)行；B依言執(zhí)行，再將結(jié)果給A；A再繼續(xù)操作。

例子還是用之前的賣票例子,兩個(gè)站點(diǎn)賣票，創(chuàng)建一個(gè)TicketManager，在外面調(diào)用startToSale方法，TicketManager里面sale方法加鎖，保證線程安全。

//  TicketManager.m
//  Thread
//
//  Created by Summer on 2018/12/25.
//  Copyright ? 2018 Summer. All rights reserved.
//

#import "TicketManager.h"


#define Total 50

@interface TicketManager ()

@property (nonatomic,assign) NSInteger tickets;//剩余票數(shù)
@property (nonatomic,assign) NSInteger saleCount;//賣出票數(shù)
//使用NSThread
//@property (nonatomic,strong) NSThread *threadBJ;//北京票點(diǎn)
//@property (nonatomic,strong) NSThread *threadSH;//上海票點(diǎn)
//使用NSInvocationOperation + NSOperationQueue
@property (nonatomic , strong) NSInvocationOperation *operationBJ;
@property (nonatomic , strong) NSInvocationOperation *operationSH;
@property (nonatomic , strong)  NSOperationQueue *queue;
/*
 NSLock、NSConditionLock、NSRecursiveLock、NSCondition加鎖方式都一樣，都是實(shí)現(xiàn)NSLocking協(xié)議

 */
@property (nonatomic,strong) NSCondition *condition;
@property (nonatomic , strong) dispatch_semaphore_t semaphore;

@end

@implementation TicketManager

- (instancetype)init{
    self = [super init];
    if (self) {
        _condition = [[NSCondition alloc]init];
        _semaphore = dispatch_semaphore_create(1);
        
        _tickets = Total;
//        _threadBJ = [[NSThread alloc]initWithTarget:self selector:@selector(sale) object:nil];
//        _threadSH = [[NSThread alloc]initWithTarget:self selector:@selector(sale) object:nil];
        
//        [_threadBJ setName:@"北京"];
//        [_threadSH setName:@"上海"];
        
        
        _operationBJ = [[NSInvocationOperation alloc] initWithTarget:self selector:@selector(sale) object:nil];
        [_operationBJ setName:@"北京"];
        
        _operationSH = [[NSInvocationOperation alloc] initWithTarget:self selector:@selector(sale) object:nil];
        [_operationSH setName:@"上海"];
    }
    return self;
}

- (void)sale{
    while (1) {
        //1、synchronized
        @synchronized (self) {
            if (self.tickets > 0 ) {
                [NSThread sleepForTimeInterval:0.1];
                self.tickets --;
                self.saleCount = Total - self.tickets;
                NSLog(@"%@ , 賣出 = %ld，剩余= %ld",[NSThread currentThread],(long)self.saleCount,(long)self.tickets);
            }else{
                break;//一定要break，不然就會(huì)死循環(huán)
            }
        }
//        2、NSCondition
//        [self.condition lock];
//        if (self.tickets > 0 ) {
//            [NSThread sleepForTimeInterval:0.1];
//            self.tickets --;
//            self.saleCount = Total - self.tickets;
//            NSLog(@"%@ , 賣出 = %d，剩余= %d",[NSThread currentThread].name,self.saleCount,self.tickets);
//        }else{
//            break;
//        }
//        [self.condition unlock];
//
        //3、dispatch_semaphore方式
//        dispatch_semaphore_wait(self.semaphore, DISPATCH_TIME_FOREVER);
//        if (self.tickets > 0 ) {
//            [NSThread sleepForTimeInterval:0.1];
//            self.tickets --;
//            self.saleCount = Total - self.tickets;
//            NSLog(@"%@ , 賣出 = %d，剩余= %d",[NSThread currentThread].name,self.saleCount,self.tickets);
//        }else{
//            dispatch_semaphore_signal(self.semaphore);
//            break;
//        }
//        dispatch_semaphore_signal(self.semaphore);
    }
}

- (void)startToSale{
//    [_threadSH start];
//    [_threadBJ start];
    
    _queue = [[NSOperationQueue alloc]init];
    [_queue addOperation:_operationBJ];
    [_queue addOperation:_operationSH];
    
}

輸出結(jié)果：正常賣票

省略一部分
2019-01-07 14:46:23.488836+0800 Thread[1622:63417]  , 賣出 = 45，剩余= 5
2019-01-07 14:46:23.592623+0800 Thread[1622:63417]  , 賣出 = 46，剩余= 4
2019-01-07 14:46:23.695578+0800 Thread[1622:63417]  , 賣出 = 47，剩余= 3
2019-01-07 14:46:23.798669+0800 Thread[1622:63417]  , 賣出 = 48，剩余= 2
2019-01-07 14:46:23.903085+0800 Thread[1622:63417]  , 賣出 = 49，剩余= 1
2019-01-07 14:46:24.007916+0800 Thread[1622:63417]  , 賣出 = 50，剩余= 0

到此NSOperation + NSOperationQueue就結(jié)束了，多線程系列也結(jié)束了，2019繼續(xù)加油~~

參考博客：
iOS 多線程：『NSOperation、NSOperationQueue』詳盡總結(jié)
iOS多線程慕課網(wǎng)視頻

文章鏈接：
iOS 多線程- pThread和NSThread
iOS 多線程-GCD

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iOS 多線程-NSOperation + NSOperationQueue

iOS 多線程-NSOperation + NSOperationQueue

1. NSOperation & NSOperationQueue

2.使用步驟

2.1創(chuàng)建任務(wù)

2.1.1 NSInvocationOperation

2.1.2NSBlockOperation

2.1.3 自定義類繼承NSOperation

2.2創(chuàng)建隊(duì)列

2.2.1主隊(duì)列

2.2.2其他隊(duì)列

3.添加任務(wù)到隊(duì)列

4.控制串行、并行

5. 操作依賴

6.優(yōu)先級(jí)

7.線程間的通信

8.線程安全與線程同步

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iOS 多線程-NSOperation + NSOperationQueue

1. NSOperation & NSOperationQueue

2.使用步驟

2.1創(chuàng)建任務(wù)

2.1.1 NSInvocationOperation

2.1.2NSBlockOperation

2.1.3 自定義類繼承NSOperation

2.2創(chuàng)建隊(duì)列

2.2.1主隊(duì)列

2.2.2其他隊(duì)列

3.添加任務(wù)到隊(duì)列

4.控制串行、并行

5. 操作依賴

6.優(yōu)先級(jí)

7.線程間的通信

8.線程安全與線程同步

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4.控制串行、并行