标签:线程同步
使用NSCondition对象来控制进程的同步,通过NSCondition对象的操作实现进程间的通信。NSCondition也实现了NSLocking协议,因此也可以调用lock、 unlock来实现线程的同步。NSCondition类提供以下3个方法:
wait——该方法让线程一直等待;signal——唤醒在此NSCondition对象上等待的单个线程;broadcast——唤醒在此NSCondition对象上等待的所有线程
以银行存取款为例:设置一个BOOL类型的flag来标识庄户中是否已有存款。NO表示没有存款,存款线程可以向下执行,当存款者把钱存入账户后,设置flag为YES,并调用sinal或broadcast方法唤醒其他线程;当存款者线程进入线程体后,若flag=YES,调用wait方法让改线程等待。当flag为YES时,表明账户中已有存款,取钱线程可以向下执行,当取出钱后,将flag设置为NO,并调用signal或broadcast方法唤醒其他线程;当取钱者进入线程后,如果标识为NO,就调用wait方法进行等待。
只有当取钱线程结束后,存款线程才可以存款;同样只有存款线程存款后取钱线程才可以取钱。
定义一个Acount类,里面定义draw和deposit方法,分别实现存取款操作;
#import "Acount.h" @implementation Acount NSCondition *cond; bool flag; -(id)initWithAccount:(NSString *)acount balanca:(double)balance { if(self = [super init]) { cond = [[NSCondition alloc] init]; _acount = acount; _balance = balance; } return self; } -(void)draw:(CGFloat)drawAmount { [cond lock];//add lock if(!flag) [cond wait]; else{ NSLog(@"%@ 取了%f", [NSThread currentThread].name, drawAmount); _balance -= drawAmount; NSLog(@"账户余额为%f", self.balance); flag =NO; [cond broadcast];//wake up other threads } [cond unlock]; } -(void)deposit:(CGFloat) depositAmount { [cond lock]; if(flag) [cond wait]; else { NSLog(@"%@ 存了 %f", [NSThread currentThread].name, depositAmount); _balance += depositAmount; NSLog(@"账户余额为%f", _balance); flag = YES; [cond broadcast];//wake up other threads } [cond unlock];//open lock } @end
#import "ViewController.h" @interface ViewController () @end @implementation ViewController FKAcount *acount; - (void)viewDidLoad { [super viewDidLoad]; // Do any additional setup after loading the view, typically from a nib. acount = [[FKAcount alloc] initWithAccount:@"小明" balanca:0.0]; } - (void)didReceiveMemoryWarning { [super didReceiveMemoryWarning]; // Dispose of any resources that can be recreated. } - (IBAction)drawDeposit:(id)sender { NSThread *thread1 = [[NSThread alloc] initWithTarget:self selector:@selector(draw:) object:[NSNumber numberWithFloat:800.0]]; NSThread *thread2 = [[NSThread alloc] initWithTarget:self selector:@selector(draw:) object:[NSNumber numberWithFloat:800.0]]; NSThread *thread3 = [[NSThread alloc] initWithTarget:self selector:@selector(deposit:) object:[NSNumber numberWithFloat:800.0]]; [thread1 start]; [thread2 start]; [thread3 start]; } -(void)draw:(NSNumber*) drawAmount { [NSThread currentThread].name = @"取"; for(int i=0 ;i < 50; i++) [acount draw:drawAmount.doubleValue]; } -(void)deposit:(NSNumber *) depositAmount { [NSThread currentThread].name = @"存"; for(int i=0; i < 50; i++) [acount deposit:depositAmount.doubleValue]; } @end程序最后被阻塞无法继续向下执行,因为创建2个取款线程共100次取款操作,而1个存钱线程50次操作,程序最后被阻塞。
标签:线程同步
原文地址:http://blog.csdn.net/codebat/article/details/41008305