多线程一

一、线程方式:NSThread，NSQueueOperation, GCD, pthread

二、僵尸线程问题（NSThead操作）

• 在子线程添加定时器，如果在主线程中移除定时器会造成僵尸线程。
  1、在子线程添加定时器，必须要执行[[NSRunLoop currentRunLoop] run]。因为runloop中的资源没被移除。
  2、在子线程中无法执行到NSLog(@"runloop finished")这段代码。
  3、触摸屏幕时，将定时器从runloop中移除，但是定时器的时间依旧还在执行。

- (void)viewDidLoad {
    [super viewDidLoad];
    NSString * str = @"12211212";
    [NSThread detachNewThreadSelector:@selector(threadEvent:) toTarget:self withObject:str];
}
- (void)threadEvent:(id)thread{
    NSLog(@"%@",[NSThread currentThread]);
    //self.timer = [NSTimer scheduledTimerWithTimeInterval:2 target:self selector:@selector(timeEvent:) userInfo:@"2121" repeats:YES];
    self.timer = [NSTimer timerWithTimeInterval:2 target:self selector:@selector(timeEvent:) userInfo:nil repeats:YES];
    //使用 NSRunLoopCommonModes 模式，这个模式相当于 NSDefaultRunLoopMode 和 NSEventTrackingRunLoopMode 的结合
    [[NSRunLoop currentRunLoop] addTimer:self.timer forMode:NSDefaultRunLoopMode];
    [[NSRunLoop currentRunLoop] run];
    NSLog(@"runloop finished");
}
- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event{
    [self.timer invalidate];
}
- (void)timeEvent:(NSTimer *)sender{
    //定时器事件在子线程中执行
    NSLog(@"%@",[NSThread currentThread]);
    NSLog(@"%s",__func__);
}

线程依旧存在，如图一所示。

图一 僵尸线程图.png

• 如何解决僵尸线程
  在该线程中移除掉定时器。

- (void)viewDidLoad {
    [super viewDidLoad];
    self.thread = [[NSThread alloc] initWithTarget:self selector:@selector(threadEvent:) object:self];
    [self.thread start];
}
- (void)threadEvent:(id)thread{
    NSLog(@"%@",[NSThread currentThread]);
    //self.timer = [NSTimer scheduledTimerWithTimeInterval:2 target:self selector:@selector(timeEvent:) userInfo:@"2121" repeats:YES];
    self.timer = [NSTimer timerWithTimeInterval:2 target:self selector:@selector(timeEvent:) userInfo:nil repeats:YES];
    //使用 NSRunLoopCommonModes 模式，这个模式相当于 NSDefaultRunLoopMode 和 NSEventTrackingRunLoopMode 的结合
    [[NSRunLoop currentRunLoop] addTimer:self.timer forMode:NSDefaultRunLoopMode];
    [[NSRunLoop currentRunLoop] run];
    NSLog(@"runloop finished");
}
- (void)timeInvalidate:(id)sender{
    [self.timer invalidate];
}

- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event{
/*
  You cannot cancel messages queued using this method. 
  If you want the option of canceling a message on the current thread, 
  you must use either the performSelector:withObject:afterDelay: or performSelector:withObject:afterDelay:inModes: method.
要想自线程消灭掉，必须在其子线程中执行performSelector:withObject:afterDelay:或者performSelector:withObject:afterDelay:inModes: 方法
*/
    [self performSelector:@selector(timeInvalidate:) onThread:self.thread withObject:@"e" waitUntilDone:YES];
}
- (void)timeEvent:(NSTimer *)sender{
    //定时器事件在子线程中执行
    NSLog(@"%@",[NSThread currentThread]);
    NSLog(@"%s",__func__);
}

但是依旧不能解决僵尸线程的问题，因为在移除定时器的同时，给runLoop中添加一个timeInvalidate方法。

• 彻底解决僵尸线程
  1、方法一：

- (void)viewDidLoad {
    [super viewDidLoad];
    self.thread = [[NSThread alloc] initWithTarget:self selector:@selector(threadEvent:) object:self];
    [self.thread start];
}
- (void)threadEvent:(id)thread{
    NSLog(@"%@",[NSThread currentThread]);
    //self.timer = [NSTimer scheduledTimerWithTimeInterval:2 target:self selector:@selector(timeEvent:) userInfo:@"2121" repeats:YES];
    self.timer = [NSTimer timerWithTimeInterval:2 target:self selector:@selector(timeEvent:) userInfo:nil repeats:YES];
    //使用 NSRunLoopCommonModes 模式，这个模式相当于 NSDefaultRunLoopMode 和 NSEventTrackingRunLoopMode 的结合
    [[NSRunLoop currentRunLoop] addTimer:self.timer forMode:NSDefaultRunLoopMode];
    [self performSelector:@selector(timeInvalidate:) withObject:nil afterDelay:5];
    [[NSRunLoop currentRunLoop] run];
    NSLog(@"runloop finished");
}
- (void)timeInvalidate:(id)sender{
    [self.timer invalidate];
}
- (void)timeEvent:(NSTimer *)sender{
    //定时器事件在子线程中执行
    NSLog(@"%@",[NSThread currentThread]);
    NSLog(@"%s",__func__);
}

2、方法二：

- (void)viewDidLoad {
    [super viewDidLoad];
    _flag = NO;
    self.thread = [[NSThread alloc] initWithTarget:self selector:@selector(threadEvent:) object:self];
    [self.thread start];
}
- (void)threadEvent:(id)thread{
    NSLog(@"%@",[NSThread currentThread]);
    self.timer = [NSTimer timerWithTimeInterval:2 target:self selector:@selector(timeEvent:) userInfo:nil repeats:YES];
    //使用 NSRunLoopCommonModes 模式，这个模式相当于 NSDefaultRunLoopMode 和 NSEventTrackingRunLoopMode 的结合
    [[NSRunLoop currentRunLoop] addTimer:self.timer forMode:NSDefaultRunLoopMode];
    [[NSRunLoop currentRunLoop] run];
    NSLog(@"runloop finished");
}
- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event{
    self.flag = YES;
}
- (void)timeEvent:(NSTimer *)sender{
    //定时器事件在子线程中执行
    NSLog(@"%@",[NSThread currentThread]);
    NSLog(@"%s",__func__);
    if(self.flag == YES){
        [self.timer invalidate];
        self.timer = nil;
    }
}

• 在runloop中添加port，如果在其它线程中移除掉，会产生僵尸线程。

- (void)viewDidLoad {
    [super viewDidLoad];
    self.thread = [[NSThread alloc] initWithTarget:self selector:@selector(threadEvent:) object:self];
    [self.thread start];
}
- (void)threadEvent:(id)thread{
    NSLog(@"start");
    self.myRunLoop = [NSRunLoop currentRunLoop];
    self.port = [[NSPort alloc] init];
    [self.myRunLoop addPort:self.port forMode:NSRunLoopCommonModes];
    [self.myRunLoop run];
    NSLog(@"finished");
}
- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event{
    [self.myRunLoop removePort:self.port forMode:NSRunLoopCommonModes];
}

• 解决在runloop中添加port产生僵尸线程

- (void)viewDidLoad {
    [super viewDidLoad];
    self.thread = [[NSThread alloc] initWithTarget:self selector:@selector(threadEvent:) object:self];
    [self.thread start];
}
- (void)threadEvent:(id)thread{
    NSLog(@"start");
    self.myRunLoop = [NSRunLoop currentRunLoop];
    self.port = [[NSPort alloc] init];
    [self.myRunLoop addPort:self.port forMode:NSRunLoopCommonModes];
    [self performSelector:@selector(portCancel) withObject:nil afterDelay:5];
    [self.myRunLoop run];
    NSLog(@"finished");
}
- (void)portCancel{
    [self.myRunLoop removePort:self.port forMode:NSRunLoopCommonModes];
}

结论：
在子线程中，给runloop添加资源，必须在该线程中进行释放，否则会产生僵尸线程。

三、线程队列NSQueueOperation

3.1 Operation对象的并发和非并发

3.2 系统的Operation对象

3.2.1 NSBlockOperation

- (void)viewDidLoad {
    [super viewDidLoad];
    
    NSOperationQueue * queue = [[NSOperationQueue alloc] init];
    queue.maxConcurrentOperationCount = 2;
    NSBlockOperation * blockOperation = [[NSBlockOperation alloc] init];
    [blockOperation addExecutionBlock:^{
        NSLog(@"%@",[NSThread currentThread]);
    }];
    [blockOperation addExecutionBlock:^{
        NSLog(@"%@",[NSThread currentThread]);
    }];
    [blockOperation addExecutionBlock:^{
        NSLog(@"%@",[NSThread currentThread]);
    }];
    [blockOperation addExecutionBlock:^{
        NSLog(@"%@",[NSThread currentThread]);
    }];
    [blockOperation addExecutionBlock:^{
        NSLog(@"%@",[NSThread currentThread]);
    }];
    [blockOperation addExecutionBlock:^{
        NSLog(@"%@",[NSThread currentThread]);
    }];
    [blockOperation addExecutionBlock:^{
        NSLog(@"%@",[NSThread currentThread]);
    }];
    [queue addOperation:blockOperation];
}

打印结果：

{number = 5, name = (null)}
{number = 4, name = (null)}
{number = 6, name = (null)}
{number = 3, name = (null)}
{number = 5, name = (null)}
{number = 4, name = (null)}
{number = 6, name = (null)}

3.3.2 NSInvocationOperation(NSInvocation)

• 使用initWithTarget:selector:object:开启线程。缺点：只能传递一个参数。

- (void)viewDidLoad {
    [super viewDidLoad];
    NSOperationQueue * queue = [[NSOperationQueue alloc] init];
    NSInvocationOperation * invocationOperation = [[NSInvocationOperation alloc] initWithTarget:self selector:@selector(invocationOperationEvent) object:nil];  
    [queue addOperation:invocationOperation];
}
- (void)invocationOperationEvent{
    NSLog(@"%@",[NSThread currentThread]);
}

• 使用NSInvocation传递多个参数

- (void)viewDidLoad {
    [super viewDidLoad];
    NSOperationQueue * queue = [[NSOperationQueue alloc] init];
    NSMethodSignature * signature = [self methodSignatureForSelector:@selector(name:andAge:andSex:)];
    NSInvocation * invocation = [NSInvocation invocationWithMethodSignature:signature];
    invocation.selector = @selector(name:andAge:andSex:);
    invocation.target = self;
    NSString * name = @"Jerry";
    NSString * age = @"2";
    NSString * sex = @"男";
    //这里的index要从2开始，前两个已经被target和selector占用
    [invocation setArgument:&name atIndex:2];
    [invocation setArgument:&age atIndex:3];
    [invocation setArgument:&sex atIndex:4];
    NSInvocationOperation * invocationOperation = [[NSInvocationOperation alloc] initWithInvocation:invocation];
    [queue addOperation:invocationOperation];
}
- (void)name:(NSString *)name andAge:(NSString *)age andSex:(NSString *)sex{
    NSLog(@"name = %@,age = %@,sex = %@",name,age,sex);
}

3.3 自定义Operation对象

3.3.1 Operation状态（KVO通知）

• 当isFinished状态为NO时，NSOperation不能执行dealloc。

@interface CustomOperation : NSOperation
@end
@implementation CustomOperation
@synthesize finished = _finished;
- (void)dealloc{
    NSLog(@"%s",__func__);  
}
- (BOOL)isFinished{
    return _finished;
}
@end

- (void)viewDidLoad {
    [super viewDidLoad];
    NSOperationQueue * queue = [NSOperationQueue new];
    CustomOperation * customOperation = [CustomOperation new];
    [queue addOperation:customOperation];
}

CustomOperation不能执行dealloc,用KVO的形式，改变isFinished的值为YES,才能执行CustomOperation才能被释放。

        [self willChangeValueForKey:@"isFinished"];//_finished,finished
        _finished = YES;
        [self didChangeValueForKey:@"isFinished"];

3.3.2 配置Operation执行行为（依赖关系，优先级等）

    NSOperationQueue * operationQueue = [[NSOperationQueue alloc] init];
    NSBlockOperation * blockOperation = [[NSBlockOperation alloc] init];
    [blockOperation addExecutionBlock:^{
        NSLog(@"NSBlockOperation = %@",[NSThread currentThread]);
    }];
    NSInvocationOperation * invocationOperation = [[NSInvocationOperation alloc] initWithTarget:self selector:@selector(invocationOperationEvent) object:nil];
    
    NSBlockOperation * blockOperation2 = [[NSBlockOperation alloc] init];
    [blockOperation addExecutionBlock:^{
        NSLog(@"NSBlockOperation2 = %@",[NSThread currentThread]);
    }];
    //在入队前处理好依赖关系
    [blockOperation addDependency:invocationOperation];
    [blockOperation2 addDependency:blockOperation];
    
    [operationQueue addOperation:blockOperation];
    [operationQueue addOperation:invocationOperation];
    [operationQueue addOperation:blockOperation2];

结果：

invocationOperation = {number = 3, name = (null)}
NSBlockOperation = {number = 4, name = (null)}
NSBlockOperation2 = {number = 3, name = (null)}

⚠️：A线程依赖B线程，B依赖C，C依赖A，这样会产生死锁。