[多线程之一]－NSThread银行取款问题

秒速五厘米 2022-08-18 13:13 158阅读 0赞

//
    //  ViewController.h
    //  银行取款问题
    #import <UIKit/UIKit.h>
    
    @interface ViewController : UIViewController
    - (IBAction)DrawBtn:(UIButton *)sender;
    
    
    @end
    
    @interface Account : NSObject
    
    @property(nonatomic, copy)NSString* AccountNo;
    //atomic属性里面加了锁了，禁止多线程同时修改。
    @property(nonatomic, assign, readwrite)CGFloat Balance;
    
    -(instancetype)initWithAccountNo:(NSString*)ANo
                             Balance:(CGFloat)ABalance;
    -(void)draw:(CGFloat)AdrawAccount;
    
    @end

//
    //  ViewController.m
    //  银行取款问题
    
    #import "ViewController.h"
    
    @interface ViewController ()
    
    @end
    
    @implementation ViewController
    
    {
        Account* a;
        NSThread* t1;
        NSThread* t2;
        NSLock* lock;
    }
    - (void)viewDidLoad {
        a = [[Account alloc] initWithAccountNo:@"12345" Balance:100];
        lock = [[NSLock alloc] init];
        [super viewDidLoad];
        // Do any additional setup after loading the view, typically from a nib.
    }
    
    -(void)drawMethod:(NSNumber*)ADrawAccount
    {
        @synchronized(a)//方法1
        {
           [a draw:[ADrawAccount doubleValue]];
        }
        
        [lock lock];//方法2
           [a draw:[ADrawAccount doubleValue]];
        [lock unlock];
    }
    
    - (void)didReceiveMemoryWarning {
        [super didReceiveMemoryWarning];
        // Dispose of any resources that can be recreated.
    }
    
    - (IBAction)DrawBtn:(UIButton *)sender {
        t1 = [[NSThread alloc] initWithTarget:self selector:@selector(drawMethod:) object:[NSNumber numberWithInt:80]];
        t2 =[[NSThread alloc] initWithTarget:self selector:@selector(drawMethod:) object:[NSNumber numberWithInt:80]];
        //注意：如果把t1和t2放到viewdidload里面定义的话，会出错，原因是线程执行完了，属于finish状态了，就不能再执行了。
        [t1 start];
        [t2 start];
    }
    @end
    
    @implementation Account
    
    -(instancetype)initWithAccountNo:(NSString *)ANo Balance:(CGFloat)ABalance
    {
        if (self = [super init]) {
            self.AccountNo = ANo;
            _Balance = ABalance;
        }
        return self;
    }
    
    -(void)draw:(CGFloat)AdrawAccount
    {
        //atomic特性没验证出来，以后再说吧。
        if (self.Balance > AdrawAccount) {
            [NSThread sleepForTimeInterval:0.1];//为了试验余额为负数，特此加了延迟。妥妥复现。
            self.Balance = self.Balance - AdrawAccount;
            NSLog(@"%@取款成功,取款金额%f",[NSThread currentThread].name,AdrawAccount);
            NSLog(@"账户%@，余额为：%f", self.AccountNo,_Balance);
        }
        else
        {
            NSLog(@"%@取款失败，余额不足!",[NSThread currentThread].name);
        }
    }
    
    @end

摘自《疯狂iOS》下册。