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

多线程 线程同步问题

多线程线程同步问题