iOS多线程问题演示

demo1.m

MultiThreadObject *object = [[MultiThreadObject alloc] init];
NSLock *lock = [[NSLock alloc] init];
[NSThread detachNewThreadWithBlock:^{
    NSInteger loopCount = 1000;
    while (loopCount) {
        [lock lock];
        NSArray *data = @[@"1", @"2", @"3"];
        object.data = data;
        if (object.data != data) {
            NSLog(@"多线程同步问题 self.data: %@, data: %@",object.data, data);
        }
        loopCount --;
        [lock unlock];
    }
}];
[NSThread detachNewThreadWithBlock:^{
    NSInteger loopCount = 1000;
    while (loopCount) {
        [lock lock];
        NSArray *data = @[@"1", @"2", @"3", @"4"];
        object.data = data;
        loopCount --;
        [lock unlock];
    }
}];

MultiThreadObject.m

@interface MultiThreadObject: NSObject
@property (nonatomic, strong) NSArray *data;
@end

@implementation MultiThreadObject
@end

重现步骤

1. 创建一个共享变量object，其类型为MultiThreadObject
2. 开启两个线程，对object.data设值，在同一个线程中，设置值后立马取出来和传入参数进行对比
3. 如果不加锁（NSLock，synchronized等），在控制台会输出“多线程同步问题...”
4. 如果加锁，结果如预期。