@interface ViewController ()    @property (nonatomic, strong) NSMutableArray * array;    @property (nonatomic, strong) NSCondition * condition;    @property (nonatomic, strong) NSTimer * timer;    @end      @implementation ViewController    //初始化    - (NSMutableArray *)array    {        if (!_array) {            _array = [NSMutableArray array];        }        return _array;    }      - (NSCondition *)condition    {        if (!_condition) {            _condition = [[NSCondition alloc] init];        }        return  _condition;    }      //加载    - (void)viewDidLoad {        [super viewDidLoad];                //购买        for (int i = 0; i<3; i++)        {            [self performSelectorInBackground:@selector(_consumer) withObject:nil];        }                //生产        self.timer = [NSTimer scheduledTimerWithTimeInterval:2 target:self selector:@selector(_productor) userInfo:nil repeats:YES];            }      - (void)_productor    {        [self.condition lock];                if (self.array.count != 0)        {            NSLog(@"结束");            [self.timer invalidate];            self.timer = nil;        }        else        {            [self.array addObject:@"aaa"];            NSLog(@"生产完成！");            [self.condition signal];        }                [self.condition unlock];                    }        - (void)_consumer    {        [self.condition lock];                if (self.array.count <= 0)        {            NSLog(@"正在等待！");            [self.condition wait];        }                [self.array removeLastObject];        NSLog(@"购买成功！");                [self.condition unlock];    }        @end