版本记录
| 版本号 | 时间 |
|---|---|
| V1.0 | 2017.08.16 |
前言
信号量机制是多线程通信中的比较重要的一部分，对于
NSOperation可以设置并发数，但是对于GCD就不能设置并发数了，那么就只能靠信号量机制了。接下来这几篇就会详细的说一下并发机制。感兴趣的可以看这几篇文章。
1. iOS与多线程（一） —— GCD中的信号量及几个重要函数
2. iOS与多线程（二） —— NSOperation实现多并发之创建任务
3. iOS与多线程（三） —— NSOperation实现多并发之创建队列和开启线程
NSOperation串并行的实现
NSOperation的串并行是通过设置最大并发数maxConcurrentOperationCount来实现的。
- 当
maxConcurrentOperationCount为1时，就是串行执行 - 当
maxConcurrentOperationCount > 1时，就是并行执行
不管是串行还是并行，开启的线程数目是系统决定的，并不是我们决定的。
1. 串行
下面我们看一下代码。
#import "JJSerialConquenceVC.h"
@interface JJSerialConquenceVC ()
@end
@implementation JJSerialConquenceVC
#pragma mark - Override Base Function
- (void)viewDidLoad
{
[super viewDidLoad];
self.view.backgroundColor = [UIColor whiteColor];
//创建队列
NSOperationQueue *queue = [[NSOperationQueue alloc] init];
//设置并发数
queue.maxConcurrentOperationCount = 1;
[queue addOperationWithBlock:^{
NSLog(@"1_thread = %@",[NSThread currentThread]);
}];
[queue addOperationWithBlock:^{
NSLog(@"2_thread = %@",[NSThread currentThread]);
}];
[queue addOperationWithBlock:^{
NSLog(@"3_thread = %@",[NSThread currentThread]);
}];
[queue addOperationWithBlock:^{
NSLog(@"4_thread = %@",[NSThread currentThread]);
}];
[queue addOperationWithBlock:^{
NSLog(@"5_thread = %@",[NSThread currentThread]);
}];
[queue addOperationWithBlock:^{
NSLog(@"6_thread = %@",[NSThread currentThread]);
}];
}
@end
下面看输出结果
2017-08-16 17:58:58.090660+0800 JJOC[10149:4513595] 1_thread = <NSThread: 0x170276740>{number = 4, name = (null)}
2017-08-16 17:58:58.090813+0800 JJOC[10149:4513595] 2_thread = <NSThread: 0x170276740>{number = 4, name = (null)}
2017-08-16 17:58:58.090868+0800 JJOC[10149:4513595] 3_thread = <NSThread: 0x170276740>{number = 4, name = (null)}
2017-08-16 17:58:58.090919+0800 JJOC[10149:4513595] 4_thread = <NSThread: 0x170276740>{number = 4, name = (null)}
2017-08-16 17:58:58.090967+0800 JJOC[10149:4513595] 5_thread = <NSThread: 0x170276740>{number = 4, name = (null)}
2017-08-16 17:58:58.091014+0800 JJOC[10149:4513595] 6_thread = <NSThread: 0x170276740>{number = 4, name = (null)}
可见，是串行执行的，而且系统只给开了一个线程。
2. 并行
下面我们看一下并行下的代码。
#import "JJSerialConquenceVC.h"
@interface JJSerialConquenceVC ()
@end
@implementation JJSerialConquenceVC
#pragma mark - Override Base Function
- (void)viewDidLoad
{
[super viewDidLoad];
self.view.backgroundColor = [UIColor whiteColor];
//创建队列
NSOperationQueue *queue = [[NSOperationQueue alloc] init];
//设置并发数
queue.maxConcurrentOperationCount = 3;
[queue addOperationWithBlock:^{
NSLog(@"1_thread = %@",[NSThread currentThread]);
sleep(1);
}];
[queue addOperationWithBlock:^{
NSLog(@"2_thread = %@",[NSThread currentThread]);
sleep(1);
}];
[queue addOperationWithBlock:^{
NSLog(@"3_thread = %@",[NSThread currentThread]);
sleep(1);
}];
[queue addOperationWithBlock:^{
NSLog(@"4_thread = %@",[NSThread currentThread]);
sleep(1);
}];
[queue addOperationWithBlock:^{
NSLog(@"5_thread = %@",[NSThread currentThread]);
sleep(1);
}];
[queue addOperationWithBlock:^{
NSLog(@"6_thread = %@",[NSThread currentThread]);
sleep(1);
}];
}
@end
看输出结果
2017-08-16 18:02:38.893083+0800 JJOC[10154:4514418] 1_thread = <NSThread: 0x1742716c0>{number = 4, name = (null)}
2017-08-16 18:02:38.893199+0800 JJOC[10154:4514414] 2_thread = <NSThread: 0x1700746c0>{number = 3, name = (null)}
2017-08-16 18:02:38.893644+0800 JJOC[10154:4514415] 3_thread = <NSThread: 0x174271840>{number = 5, name = (null)}
2017-08-16 18:02:39.897629+0800 JJOC[10154:4514414] 5_thread = <NSThread: 0x1700746c0>{number = 3, name = (null)}
2017-08-16 18:02:39.897613+0800 JJOC[10154:4514418] 4_thread = <NSThread: 0x1742716c0>{number = 4, name = (null)}
2017-08-16 18:02:39.898884+0800 JJOC[10154:4514415] 6_thread = <NSThread: 0x174271840>{number = 5, name = (null)}
可以看见系统给开启了3个线程，执行顺序也变成了123546，说明是并行的。
操作依赖
有的时候我们希望执行完一个任务再去执行另外一个任务，这个时候就需要操作依赖了。比如说A、B两个操作，我们希望执行完A操作以后再去执行B操作，那么我们就可以设置B依赖于A，具体就是使用方法addDependency:。
下面还是直接看代码。
#import "JJAddDependencyVC.h"
@interface JJAddDependencyVC ()
@end
@implementation JJAddDependencyVC
#pragma mark - Override Base Function
- (void)viewDidLoad
{
[super viewDidLoad];
//创建队列
NSOperationQueue *queue = [[NSOperationQueue alloc] init];
NSBlockOperation *operation1 = [NSBlockOperation blockOperationWithBlock:^{
NSLog(@"1_thread = %@",[NSThread currentThread]);
}];
NSBlockOperation *operation2 = [NSBlockOperation blockOperationWithBlock:^{
NSLog(@"2_thread = %@",[NSThread currentThread]);
}];
[operation2 addDependency:operation1];
[queue addOperation:operation1];
[queue addOperation:operation2];
}
@end
下面看输出结果
2017-08-16 18:15:05.030277+0800 JJOC[10159:4515800] 1_thread = <NSThread: 0x17007d5c0>{number = 4, name = (null)}
2017-08-16 18:15:05.030469+0800 JJOC[10159:4515800] 2_thread = <NSThread: 0x17007d5c0>{number = 4, name = (null)}
可见，通过操作依赖实现了运行顺序的控制。
下面说一点题外话，就是GCD中线程同步的实现。
group实现
#import "JJGCDGroupVC.h"
@interface JJGCDGroupVC ()
@end
@implementation JJGCDGroupVC
#pragma mark - Override Base Function
- (void)viewDidLoad
{
[super viewDidLoad];
dispatch_queue_t queue = dispatch_queue_create(0, 0);
dispatch_group_t group = dispatch_group_create();
dispatch_group_enter(group);
dispatch_group_async(group, queue, ^{
NSLog(@"task 1 on %@",[NSThread currentThread]);
dispatch_group_leave(group);
});
dispatch_group_enter(group);
dispatch_group_async(group, queue, ^{
NSLog(@"task 2 on %@",[NSThread currentThread]);
dispatch_group_leave(group);
});
dispatch_group_notify( group, queue, ^{
NSLog( @"all task done %@", [NSThread currentThread] );
NSLog(@"可以执行其他的任务了");
} );
}
@end
下面看输出结果
2017-08-16 18:35:32.894210+0800 JJOC[10163:4518939] task 1 on <NSThread: 0x174079900>{number = 4, name = (null)}
2017-08-16 18:35:32.894343+0800 JJOC[10163:4518939] task 2 on <NSThread: 0x174079900>{number = 4, name = (null)}
2017-08-16 18:35:32.894393+0800 JJOC[10163:4518939] all task done <NSThread: 0x174079900>{number = 4, name = (null)}
2017-08-16 18:35:32.894424+0800 JJOC[10163:4518939] 可以执行其他的任务了
可见开启了线程并实现了任务的同步。
信号量semaphore实现
dispatch_semaphore_t sem = dispatch_semaphore_create(0);
[networkManager requestWithDelay:5 completion:^{
dispatch_semaphore_signal(sem);//+1
}];
dispatch_semaphore_wait(sem, DISPATCH_TIME_FOREVER);//-1
NSLog(@"OK");
信号量方面的知识，前几篇已经说过了，这里很清晰的是等待网络请求结束，才可以行NSLog(@"OK");这段代码。
barrier
barrier阻塞的使用起来就很方便了，它就相当于一个栅栏，将不同的任务块区分开来，如下图所示。
barrier
这里需要主要的是，barrier只能用于并发队列不能用于全局队列。
下面看代码。
#import "JJGCDBarrierVC.h"
@interface JJGCDBarrierVC ()
@end
@implementation JJGCDBarrierVC
#pragma mark - Override Base Function
- (void)viewDidLoad
{
[super viewDidLoad];
//创建并发队列
dispatch_queue_t queue = dispatch_queue_create("cc.imguiqing", DISPATCH_QUEUE_CONCURRENT);
//开启异步任务
dispatch_async(queue, ^{
NSLog(@"task 1 on %@",[NSThread currentThread]);
});
dispatch_async(queue, ^{
NSLog(@"task 2 on %@",[NSThread currentThread]);
});
dispatch_barrier_async(queue, ^{
NSLog(@"barrier ==========");
});
dispatch_async(queue, ^{
NSLog(@"task 3 on %@",[NSThread currentThread]);
});
}
@end
下面看输出结果
2017-08-16 18:49:07.271659+0800 JJOC[10166:4521475] task 1 on <NSThread: 0x174078380>{number = 3, name = (null)}
2017-08-16 18:49:07.271736+0800 JJOC[10166:4521478] task 2 on <NSThread: 0x170261b80>{number = 4, name = (null)}
2017-08-16 18:49:07.271761+0800 JJOC[10166:4521478] barrier ==========
2017-08-16 18:49:07.271799+0800 JJOC[10166:4521478] task 3 on <NSThread: 0x170261b80>{number = 4, name = (null)}
这个很好理解就不多说了。
一些其他方法
1. - (void)cancel;
-
NSOperation类中的方法，取消单个操作，这里的取消不是立即取消操作，而是当前的操作完成以后不再继续执行新的操作。
2. - (void)cancelAllOperations;
-
NSOperationQueue中的方法，取消队列中的所有操作。
3. @property (getter=isSuspended) BOOL suspended;
-
NSOperationQueue中只读属性，用来判断队列是否暂停。
上面所说的名词，暂停和取消是有区别的，暂停的意思就是操作以后还可以回复，而取消的意思就是所有的操作清空，不能继续执行其他的剩下的操作了。
后记
未完，待续~~~
秋
