iOS多线程-读写安全方案

原则

• “多读单写” 只能有1个线程进行写的操作 允许有多个线程进行读的操作
• 不允许既有写的操作，又有读的操作

应用场景：用于文件等数据的读写操作

1、pthread_rwlock：读写锁

#import <pthread.h>

@interface ViewController ()
@property (assign, nonatomic) pthread_rwlock_t lock;
@end

- (void)viewDidLoad {
    [super viewDidLoad];
    // 初始化锁
    pthread_rwlock_init(&_lock, NULL);
    
    dispatch_queue_t queue = dispatch_get_global_queue(0, 0);
    
    for (int i = 0; i < 10; i++) {
        dispatch_async(queue, ^{
            [self read];
        });
        dispatch_async(queue, ^{
            [self write];
        });
    }
}

- (void)read {
    pthread_rwlock_rdlock(&_lock);
    
    sleep(1);
    NSLog(@"%s", __func__);
    
    pthread_rwlock_unlock(&_lock);
}

- (void)write{
    pthread_rwlock_wrlock(&_lock);
    
    sleep(1);
    NSLog(@"%s", __func__);
    
    pthread_rwlock_unlock(&_lock);
}

- (void)dealloc{
    pthread_rwlock_destroy(&_lock);
}

2、dispatch_barrier_async：异步栅栏调用 dispatch_barrier_async函数传入的并发队列，必须是自己通过dispatch_queue_cretate创建的。如果传入的是一个串行或一个全局的并发队列，那这个函数便等同于dispatch_async函数的效果。

//初始化队列
self.queue = dispatch_queue_create("rw_queue", DISPATCH_QUEUE_CONCURRENT);

- (void)read {
    dispatch_async(self.queue, ^{
        sleep(1);
        NSLog(@"read");
    });
}
- (void)write
{
    dispatch_barrier_async(self.queue, ^{
        sleep(1);
        NSLog(@"write");
    });
}