多线程之NSOperation小结

一、NSOperation 抽象类

• NSOperation 是一个"抽象类"，不能直接使用。抽象类的用处是定义子类共有的属性和方法。

• NSOperation 是基于 GCD 做的面向对象的封装。
• 相比较 GCD 使用更加简单，并且提供了一些用 GCD 不是很好实现的功能。
• 苹果公司推荐使用的并发技术。

• 两个子类：
• NSInvocationOperation (调用)
• NSBlockOperation (块)

相比NSInvocationOperation推荐使用NSBlockOperation，代码简单，同时由于闭包性使它没有传参问题。

• NSOperationQueue 队列

已经学习过的抽象类

• UIGestureRecognizer
• CAAnimation
• CAPropertyAnimation

二、 NSOperation 和 GCD 的核心概念

• GCD的核心概念：将 任务(block) 添加到队列，并且指定执行任务的函数。
• NSOperation 的核心概念：将 操作 添加到 队列。

三、NSOperation 和 GCD的区别：

GCD

• 将任务（block）添加到队列(串行/并发/主队列)，并且指定任务执行的函数(同步/异步)
• GCD是底层的C语言构成的API
• iOS 4.0 推出的，针对多核处理器的并发技术
• 在队列中执行的是由 block 构成的任务，这是一个轻量级的数据结构
• 要停止已经加入 queue 的 block 需要写复杂的代码
• 需要通过 Barrier 或者同步任务设置任务之间的依赖关系
• 只能设置队列的优先级
• 高级功能：
• 一次性 once
• 延迟操作 after
• 调度组

NSOperation

• 核心概念：把操作(异步)添加到队列。
• OC 框架，更加面向对象，是对 GCD 的封装。
• iOS 2.0 推出的，苹果推出 GCD 之后，对 NSOperation 的底层全部重写。
• Operation作为一个对象，为我们提供了更多的选择。
• 可以跨队列设置操作的依赖关系
• 可以设置队列中每一个操作的优先级
• 高级功能：
• 最大操作并发数(GCD不好做)
• 继续/暂停/全部取消
• 跨队列设置操作的依赖关系

四、代码实践

//
//  ViewController.m
//  NSOperationTest
//
//  Created by mayl on 2018/1/5.
//  Copyright © 2018年. All rights reserved.
//

#import "ViewController.h"

@interface ViewController ()
@property(nonatomic, strong) NSOperationQueue *gOpQueue;
@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    [self setUpUI];
    
//    [self aysncCon];
    [self maxConCount];
//    [self oftenUse];
//    [self setUpDependence];
//    [self waitUntilFinished];
}

- (void)setUpUI{
    
    //暂停，继续按钮
    UIButton *lBtn4Pause = [UIButton buttonWithType:UIButtonTypeCustom];
    [self.view addSubview:lBtn4Pause];
    
    lBtn4Pause.frame = CGRectMake(10, 100, 100, 50);
    [lBtn4Pause setTitle:@"挂起" forState:UIControlStateNormal];
    lBtn4Pause.titleLabel.numberOfLines = 0;
    [lBtn4Pause setTitleColor:[UIColor blackColor] forState:UIControlStateNormal];
    [lBtn4Pause addTarget:self action:@selector(pauseBtnDidClick:) forControlEvents:UIControlEventTouchUpInside];
    
    //取消所有任务按钮
    UIButton *lBtn4CancelAll = [UIButton buttonWithType:UIButtonTypeCustom];
    [self.view addSubview:lBtn4CancelAll];
    
    lBtn4CancelAll.frame = CGRectMake(150, 100, 100, 50);
    [lBtn4CancelAll setTitle:@"cancel all" forState:UIControlStateNormal];
    [lBtn4CancelAll setTitleColor:[UIColor redColor] forState:UIControlStateNormal];
    [lBtn4CancelAll addTarget:self action:@selector(cancelAllBtnDidClick:) forControlEvents:UIControlEventTouchUpInside];
}

#pragma mark -  action

/**
 队列挂起，当前"没有完成的操作"，是包含在队列的操作数中的。
 队列挂起，不会影响已经执行操作的执行状态。
 队列一旦被挂起，再添加的操作不会被调度。
 */
- (void)pauseBtnDidClick:(UIButton *)btn{
    NSLog(@"队列中操作数：%zd", self.gOpQueue.operationCount);
    if (0 == self.gOpQueue.operationCount) {
        NSLog(@"队列中无操作");
        return;
    }
    
    NSLog(@"3:%d", self.gOpQueue.isSuspended);
    self.gOpQueue.suspended = !self.gOpQueue.isSuspended;
    NSLog(@"4:%d", self.gOpQueue.isSuspended);
    if (self.gOpQueue.isSuspended) {
        NSLog(@"队列挂起");
        [btn setTitle:@"继续"
             forState:UIControlStateNormal];
    }else{
        NSLog(@"队列继续");
        [btn setTitle:@"挂起"
             forState:UIControlStateNormal];
    }
}

/**
 取消队列中所有的操作。
 不会取消正在执行中的操作。
 不会影响队列的挂起状态
 */
- (void)cancelAllBtnDidClick:(UIButton *)btn{
    if (0 == self.gOpQueue.operationCount) {
        NSLog(@"队列中无操作");
        return;
    }
    
    NSLog(@"取消队列中所有操作,此方法不会改变队列挂起状态");
    [self.gOpQueue cancelAllOperations];
    
    NSLog(@"1:%d", self.gOpQueue.isSuspended);
    self.gOpQueue.suspended = !self.gOpQueue.isSuspended;
    NSLog(@"2:%d", self.gOpQueue.isSuspended);
}

/** 默认是：异步，并发 */
- (void)aysncCon{
    NSOperationQueue *lQueue = [[NSOperationQueue alloc] init];
    for (int i = 0; i < 20; ++i) {
        [lQueue addOperationWithBlock:^{
            [NSThread sleepForTimeInterval:1];
            NSLog(@"%d,%@", i, [NSThread currentThread]);
        }];
    }
}

/** 最大并发数:The maximum number of queued operations that can execute at the same time.*/
- (void)maxConCount{
    NSOperationQueue *lQueue = [[NSOperationQueue alloc] init];
    lQueue.maxConcurrentOperationCount = 2;
    for (int i = 0; i < 30; ++i) {
        [lQueue addOperationWithBlock:^{
            [NSThread sleepForTimeInterval:1];
            NSLog(@"%d,%@", i, [NSThread currentThread]);
        }];
    }
    
    self.gOpQueue = lQueue;
}

/** 常用：子线程耗时，主线程更新UI */
- (void)oftenUse{
    NSOperationQueue *lQ = [[NSOperationQueue alloc] init];
    
    [lQ addOperationWithBlock:^{
        NSLog(@"耗时操作开始,%@", [NSThread currentThread]);
        [NSThread sleepForTimeInterval:3];
        NSLog(@"耗时操作结束");
        
        [[NSOperationQueue mainQueue] addOperationWithBlock:^{
            NSLog(@"主线程更新UI，%@",
                  [NSThread currentThread]);
        }];
        
    }];
}

/** 设置依赖 */
- (void)setUpDependence{
    NSOperationQueue *lQ = [[NSOperationQueue alloc] init];
    
    [lQ addOperationWithBlock:^{
        [NSThread sleepForTimeInterval:1];
        NSLog(@"do something,%@",
              [NSThread currentThread]);
    }];
    
    NSBlockOperation *lOp1 = [NSBlockOperation blockOperationWithBlock:^{
        [NSThread sleepForTimeInterval:1];
        NSLog(@"1：登录,%@",
              [NSThread currentThread]);
    }];
    
    NSBlockOperation *lOp2 = [NSBlockOperation blockOperationWithBlock:^{
        [NSThread sleepForTimeInterval:1];
        NSLog(@"2：购买点券,%@",
              [NSThread currentThread]);
    }];
    
    NSBlockOperation *lOp3 = [NSBlockOperation blockOperationWithBlock:^{
        [NSThread sleepForTimeInterval:1];
        NSLog(@"3：使用点券,%@",
              [NSThread currentThread]);
    }];
    
    NSBlockOperation *lOp4 = [NSBlockOperation blockOperationWithBlock:^{
        [NSThread sleepForTimeInterval:1];
        NSLog(@"4：返回结果,%@",
              [NSThread currentThread]);
    }];
    
    [lOp2 addDependency:lOp1];
    [lOp3 addDependency:lOp2];
    [lOp4 addDependency:lOp3];
    
    //下面加的话会循环依赖，导致任何操作都无法进行，程序不会崩溃。
//    [lOp1 addDependency:lOp4];
    
    [lQ addOperations:@[lOp4, lOp3] waitUntilFinished:NO];
    [lQ addOperations:@[lOp2, lOp1] waitUntilFinished:NO];
}

/**执行效果如下：
 2018-01-05 19:54:31.721539+0800 NSOperationTest[578:156322] come in
 2018-01-05 19:54:33.727691+0800 NSOperationTest[578:156342] 0：do others,<NSThread: 0x1c027f740>{number = 3, name = (null)}
 2018-01-05 19:54:34.731836+0800 NSOperationTest[578:156342] 1：登录,<NSThread: 0x1c027f740>{number = 3, name = (null)}
 2018-01-05 19:54:35.737375+0800 NSOperationTest[578:156342] 2：购买点券,<NSThread: 0x1c027f740>{number = 3, name = (null)}
 2018-01-05 19:54:36.742936+0800 NSOperationTest[578:156342] 3：使用点券,<NSThread: 0x1c027f740>{number = 3, name = (null)}
 2018-01-05 19:54:37.746491+0800 NSOperationTest[578:156342] 4：show Time,<NSThread: 0x1c027f740>{number = 3, name = (null)}
 2018-01-05 19:54:38.764408+0800 NSOperationTest[578:156341] 5：[lQ addOperations:@[lOp4, lOp3] waitUntilFinished:YES];实现了不设置依赖，且我需要最后执行,<NSThread: 0x1c04631c0>{number = 4, name = (null)}
 */
- (void)waitUntilFinished{
    NSOperationQueue *lQ = [[NSOperationQueue alloc] init];
    
    NSLog(@"come in");
    NSBlockOperation *lOp0 = [NSBlockOperation blockOperationWithBlock:^{
        [NSThread sleepForTimeInterval:2];
        NSLog(@"0：do others,%@",
              [NSThread currentThread]);
    }];
    
    NSBlockOperation *lOp1 = [NSBlockOperation blockOperationWithBlock:^{
        [NSThread sleepForTimeInterval:1];
        NSLog(@"1：登录,%@",
              [NSThread currentThread]);
    }];
    
    NSBlockOperation *lOp2 = [NSBlockOperation blockOperationWithBlock:^{
        [NSThread sleepForTimeInterval:1];
        NSLog(@"2：购买点券,%@",
              [NSThread currentThread]);
    }];
    
    NSBlockOperation *lOp3 = [NSBlockOperation blockOperationWithBlock:^{
        [NSThread sleepForTimeInterval:1];
        NSLog(@"3：使用点券,%@",
              [NSThread currentThread]);
    }];
    
    NSBlockOperation *lOp4 = [NSBlockOperation blockOperationWithBlock:^{
        [NSThread sleepForTimeInterval:1];
        NSLog(@"4：show Time,%@",
              [NSThread currentThread]);
    }];
    
    NSBlockOperation *lOp5 = [NSBlockOperation blockOperationWithBlock:^{
        [NSThread sleepForTimeInterval:1];
        
        NSLog(@"5：[lQ addOperations:@[lOp4, lOp3] waitUntilFinished:YES];实现了不设置依赖，且我需要最后执行,%@",
              [NSThread currentThread]);
    }];

    [lOp2 addDependency:lOp1];
    [lOp3 addDependency:lOp2];
    [lOp4 addDependency:lOp3];

    //执行顺序跟在数组中的顺序无关
    //waitUntilFinished:If YES, the current thread is blocked until all of the specified operations finish executing. If NO, the operations are added to the queue and control returns immediately to the caller.(If YES，当前线程会被阻塞，直到数组中所有操作执行完毕。下局代码是直到lOp5执行完毕，才会执行后续操作)
    [lQ addOperations:@[lOp0] waitUntilFinished:YES];
    
    [lQ addOperations:@[lOp2, lOp1] waitUntilFinished:NO];
    [lQ addOperations:@[lOp4, lOp3] waitUntilFinished:YES];
    
    [lQ addOperation:lOp5];
}

@end