多线程 线程同步问题
// DYFViewController.m// 623-05-线程同步问题//// Created by dyf on 14-6-23.// Copyright (c) 2014年 ___FULLUSERNAME___. All rights reserved.//#import "DYFViewController.h"@interface DYFViewController ()@property (nonatomic, assign) int leftCount;@property (nonatomic, strong) NSThread *thread0;@property (nonatomic, strong) NSThread *thread1;@property (nonatomic, strong) NSThread *thread2;@end@implementation DYFViewController- (void)viewDidLoad{ [super viewDidLoad]; // Do any additional setup after loading the view, typically from a nib. // 默认有100张 self.leftCount = 100; // 开启多条线程同时卖票 self.thread0 = [[NSThread alloc] initWithTarget:self selector:@selector(saleTicket) object:@"000"]; self.thread0.name = @"0000"; // 优先级 self.thread0.threadPriority = 1.0; self.thread1 = [[NSThread alloc] initWithTarget:self selector:@selector(saleTicket) object:@"000"]; self.thread1.name = @"1111"; self.thread1.threadPriority = 0.0; self.thread2 = [[NSThread alloc] initWithTarget:self selector:@selector(saleTicket) object:@"000"]; self.thread2.name = @"2222"; self.thread2.threadPriority = 0.0; }/** * 卖票 */- (void)saleTicket{// NSLock *lock = [[NSLock alloc] init];// lock.tryLock// lock.lock while (1) { @synchronized(self){ // 开始枷锁 // 1.先检查票数 int count = [self leftCount]; if (count > 0) { // 票数 - 1 [self setLeftCount:(count - 1)]; // 暂停 [NSThread sleepForTimeInterval:0.0004]; NSThread *currentT = [NSThread currentThread]; NSLog(@"%@,-------%d", currentT.name, self.leftCount); }else { // 退出线程 [NSThread exit]; } } // 解锁 }}- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event{ [self.thread0 start]; [self.thread1 start]; [self.thread2 start];}@end小结：
--------------线程的安全问题（多线程的安全隐患）-------
1.资源共享
·一块资源可能会被多个线程共享，即多个线程可能会访问同一块资源
·比如多个线程访问同一个对象，同一个变量、同一个文件
2.当多个线程访问同一块资源时，很容易引发数据错乱和数据安全问题
3.实例
eg。1 存钱取钱
eg。2 卖票
-----------------安全隐患解决-互斥锁-----
1.格式
@synchronized(锁对象)
{// 需要锁定的代码
}
注意：锁定一份代码只能用1把锁，用多把锁是无效的
2.优缺点
·优点：能有效防止多线程抢夺资源造成的安全问题
·缺点：需要消耗大量的cpu资源
3.互斥锁的使用前提：多条线程抢夺同一块资源
4.相关术语：线程同步
·means：多条线程按顺序的执行任务
·互斥锁就是使用了线程同步技术
