iOS自学之NSOperation、NSOperationQueue、Background

　　iOS中多线程编程主要分为NSThread、NSOperation和GCD，今天主要记录下自己在学习NSOperation中的点滴～如有不对的地方帮忙指出下，PS：人生第一次写blog，各位看官请轻虐，谢啦～

　　NSOperation是abstract类，不能直接使用，可以使用CocoTouch提供的NSBlockOperaion和NSInvocationOperation，也可以自己实现subclass。NSOperation可以理解为一个独立的任务，没有调度功能，真正利用NSOperation实现多线程的关键是NSOperationQueue，当NSOperation 添加到NSOperationQueue后，NSOperationQueue就会给队列中的NSOperation分配线程并调度。

1、NSOperationQueue为队列中的NSOperation分配不同的线程，测试代码如下：

- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.
    NSLog(@"main Thread is %p",[NSThread mainThread]);
    [self testOperationWithQueue];
}
- (void)testOperationWithQueue
{
    NSOperationQueue *operationQueue = [[NSOperationQueue alloc] init];
    NSBlockOperation *blockOperation1 = [NSBlockOperation blockOperationWithBlock:^{
        [NSThread sleepForTimeInterval:1];
        NSLog(@"blockOperation1:current Thread is %p",[NSThread currentThread]);
    }];
    NSBlockOperation *blockOperation2 = [NSBlockOperation blockOperationWithBlock:^{
        [NSThread sleepForTimeInterval:1];
        NSLog(@"blockOperation2:current Thread is %p",[NSThread currentThread]);
    }];
    NSBlockOperation *blockOperation3 = [NSBlockOperation blockOperationWithBlock:^{
        [NSThread sleepForTimeInterval:1];
        NSLog(@"blockOperation3:current Thread is %p",[NSThread currentThread]);
    }];
    [operationQueue addOperation:blockOperation1];
    [operationQueue addOperation:blockOperation2];
    [operationQueue addOperation:blockOperation3];
}

打印结果：
2015-05-29 23:34:22.747 TestNSOperation[12730:1171127] main Thread is 0x7fc279f28130
2015-05-29 23:34:31.288 TestNSOperation[12730:1171237] blockOperation1:current Thread is 0x7fc279e0b8a0
2015-05-29 23:34:31.288 TestNSOperation[12730:1171238] blockOperation3:current Thread is 0x7fc279d661c0
2015-05-29 23:34:31.288 TestNSOperation[12730:1171235] blockOperation2:current Thread is 0x7fc279e064c0

 

从打印结果可以看出blockOperation1、blockOperation2、blockOperation3运行于不同的线程，是同时运行的，不需要等其他NSOperation，这也表明NSOperationQueue默认是并发执行。如果想要serial执行，则可以设置operationQueue.maxConcurrentOperationCount = 1;

　　2、不用NSOperationQueue，也可以直接调用NSOperation的start方法，但此时NSOepration运行在当前线程上,测试代码如下：

- (void)testOperationNotQueue
{
    NSBlockOperation *blockOperation1 = [NSBlockOperation blockOperationWithBlock:^{
        NSLog(@"blockOperation1:current Thread is %p",[NSThread currentThread]);
    }];
    NSBlockOperation *blockOperation2 = [NSBlockOperation blockOperationWithBlock:^{
        NSLog(@"blockOperation2:current Thread is %p",[NSThread currentThread]);
    }];
    NSBlockOperation *blockOperation3 = [NSBlockOperation blockOperationWithBlock:^{
        NSLog(@"blockOperation3:current Thread is %p",[NSThread currentThread]);
    }];
    [blockOperation1 start];
    [blockOperation2 start];
    [blockOperation3 start];
}

//打印结果
2015-05-30 00:22:20.497 TestNSOperation[12968:1196358] main Thread is 0x7fb562427fd0
2015-05-30 00:22:20.498 TestNSOperation[12968:1196358] blockOperation1:current Thread is 0x7fb562427fd0
2015-05-30 00:22:20.499 TestNSOperation[12968:1196358] blockOperation2:current Thread is 0x7fb562427fd0
2015-05-30 00:22:20.499 TestNSOperation[12968:1196358] blockOperation3:current Thread is 0x7fb562427fd0

　　从打印结果可以看出blockOperation都运行在mainThread上。

　　3、NSOperation还提供了cancel功能，cancel不是强制把你的代码stop掉，只是改变了NSOperation内部的状态，该功能只能cancel掉Ready、Finish状态的NSOperation，不能cancel掉正在executing的NSOperation，测试代码如下：

- (void)testCancelOperation
{
    NSOperationQueue *operationQueue = [[NSOperationQueue alloc] init];
    NSBlockOperation *blockOperation1 = [NSBlockOperation blockOperationWithBlock:^{
        NSLog(@"start blockOperation1!");
        [NSThread sleepForTimeInterval:10];
        if(blockOperation1.isCancelled)
        {
            NSLog(@"blockOperation2 cancelled!");
            return;
        }
        NSLog(@"blockOperation1:current Thread is %p",[NSThread currentThread]);
    }];
    NSBlockOperation *blockOperation2 = [NSBlockOperation blockOperationWithBlock:^{
        NSLog(@"blockOperation2:current Thread is %p",[NSThread currentThread]);
    }];
    NSBlockOperation *blockOperation3 = [NSBlockOperation blockOperationWithBlock:^{
        NSLog(@"blockOperation3:current Thread is %p",[NSThread currentThread]);
    }];
    operationQueue.maxConcurrentOperationCount = 1;
    [operationQueue addOperation:blockOperation1];
    [operationQueue addOperation:blockOperation2];
    [operationQueue addOperation:blockOperation3];
    [NSThread sleepForTimeInterval:2];
    NSLog(@"cancel blockOperation1");
    [blockOperation1 cancel];
    NSLog(@"cancel blockOperation2");
    [blockOperation2 cancel];
    NSLog(@"cancel blockOperation3");
    [blockOperation3 cancel];
}
打印结果：
2015-05-30 00:27:26.311 TestNSOperation[13009:1199727] main Thread is 0x7ff02ae24e70
2015-05-30 00:27:26.312 TestNSOperation[13009:1199831] start blockOperation1!
2015-05-30 00:27:28.318 TestNSOperation[13009:1199727] cancel blockOperation1
2015-05-30 00:27:28.318 TestNSOperation[13009:1199727] cancel blockOperation2
2015-05-30 00:27:28.318 TestNSOperation[13009:1199727] cancel blockOperation3
2015-05-30 00:27:36.315 TestNSOperation[13009:1199831] blockOperation1:current Thread is 0x7ff02af1dec0

从打印结果可以看出不能cancel掉blockOperation1，而blockOperation2和blockOperation3则被成功地取消了。

　　4、NSOpertion还可以设置依赖，这一功能解决了需要按一定次序执行的situation，不多说直接上代码:

- (void)testOperationWithDependency
{
    NSOperationQueue *operationQueue = [[NSOperationQueue alloc] init];
    NSBlockOperation *blockOperation1 = [NSBlockOperation blockOperationWithBlock:^{
        NSLog(@"start blockOperation1");
    }];
    NSBlockOperation *blockOperation2 = [NSBlockOperation blockOperationWithBlock:^{
        [NSThread sleepForTimeInterval:2];
        NSLog(@"start blockOperation2");
    }];
    NSBlockOperation *blockOperation3 = [NSBlockOperation blockOperationWithBlock:^{
        [NSThread sleepForTimeInterval:3];
        NSLog(@"start blockOperation3");;
    }];
    [blockOperation1 addDependency:blockOperation2];
    [blockOperation2 addDependency:blockOperation3];
    [operationQueue addOperation:blockOperation1];
    [operationQueue addOperation:blockOperation2];
    [operationQueue addOperation:blockOperation3];
}
打印结果：
2015-05-31 18:18:06.649 TestNSOperation[15541:1510356] main Thread is 0x7fdaf9712a00
2015-05-31 18:18:09.654 TestNSOperation[15541:1510384] start blockOperation3
2015-05-31 18:18:11.660 TestNSOperation[15541:1510384] start blockOperation2
2015-05-31 18:18:11.660 TestNSOperation[15541:1510384] start blockOperation1

从打印的结果可以看出只有当依赖的Oepration执行完之后才开始执行自己。

　　5、当NSOperation添加到NSOperationQueue中，即使进入background（超过10min）NSOperation也会执行，真的不可思议啊，不是app进入到后台后如果不开定位服务、循环播放无声音乐、VOIP就最多运行10min吗？怎么超过10min的NSOperation还能执行啊，麻烦知道的网友告知一下，万分感谢～测试代码如下：

- (void)testBackgroundOperation
{
    NSOperationQueue *operationQueue = [[NSOperationQueue alloc] init];
    NSBlockOperation *blockOperation1 = [NSBlockOperation blockOperationWithBlock:^{
        [NSThread sleepForTimeInterval:11*60];
        NSLog(@"blockOperation1:current Thread is %p",[NSThread currentThread]);
    }];
    [operationQueue addOperation:blockOperation1];
}
打印结果：
2015-05-30 01:04:40.511 TestNSOperation[13252:1219020] main Thread is 0x7faf41c0da30
2015-05-30 01:04:43.095 TestNSOperation[13252:1219020] applicationDidEnterBackground!
2015-05-30 01:15:40.526 TestNSOperation[13252:1219146] blockOperation1:current Thread is 0x7faf41e02f90

从打印结果可以看出，进入后台11min后，blockOperation1执行了，这是为什么呀！！！！

　　6、疑问

　　1、NSOperationQueue具体如何管理NSOperation的，网上也没找到相关文章，希望知道的朋友给个链接；2、测试中发现当NSOperationQueue是局部变量，只要NSOperation添加到NSOperationQueue中，即使程序运行到超出NSOperationQueue的生命周期外（NSOperationQueue变量自动释放了），NSOperation依然可以执行，比如如下代码，operationQueue应该是释放了，但blockOperation1、blockOperation2依然运行，其实这2个疑问都是关于NSOperationQueue如何管理NSOperation的，再次恳求知道的网友给个链接，谢谢哈～

- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.
    NSLog(@"main Thread is %p",[NSThread mainThread]);
    [self testOperationLeaveLifeCycle];
    NSLog(@"leave operationQueue lifecycle");
}
- (void)testOperationLeaveLifeCycle
{
    NSOperationQueue *operationQueue = [[NSOperationQueue alloc] init];
    NSBlockOperation *blockOperation1 = [NSBlockOperation blockOperationWithBlock:^{
        [NSThread sleepForTimeInterval:10];
        NSLog(@"blockOperation1:current Thread is %p",[NSThread currentThread]);
    }];
    NSBlockOperation *blockOperation2 = [NSBlockOperation blockOperationWithBlock:^{
        [NSThread sleepForTimeInterval:20];
        NSLog(@"blockOperation2:current Thread is %p",[NSThread currentThread]);
    }];
    [operationQueue addOperation:blockOperation1];
    [operationQueue addOperation:blockOperation2];
}
打印结果：
2015-05-30 01:25:49.649 TestNSOperation[13358:1228380] main Thread is 0x7ff7e27241b0
2015-05-30 01:25:49.650 TestNSOperation[13358:1228380] leave operationQueue lifecycle
2015-05-30 01:25:59.652 TestNSOperation[13358:1228482] blockOperation1:current Thread is 0x7ff7e2517d20
2015-05-30 01:26:09.653 TestNSOperation[13358:1228481] blockOperation2:current Thread is 0x7ff7e2608a50

 备注：上述所有的测试代码放到github上了，共勉～https://github.com/iOSGeek0829/testNSOperation