[移动开发]iOS底层系列之＜44＞--多线程＜十四＞读写安全

1、介绍两种读写安全方式

需求：
1.同一时间，只能有1个线程进行写的操作
2.同一时间，可以有多个线程进行读的操作
3.同一时间，不能即有写的操作，又有读的操作

2、pthread_rwlock_t 读写专用锁

使用案例

#import "readWriteVC.h"
#import <pthread.h>

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

@implementation readWriteVC
/**
 需求：
 1.同一时间，只能有1个线程进行写的操作
 2.同一时间，可以有多个线程进行读的操作
 3.同一时间，不能即有写的操作，又有读的操作
 */
- (void)viewDidLoad {
    [super viewDidLoad];
    pthread_rwlock_init(&_lock, NULL);
    
    for (int i = 0; i < 10; i++) {
        [[[NSThread alloc] initWithTarget:self selector:@selector(read) object:nil] start];
        [[[NSThread alloc] initWithTarget:self selector:@selector(write) object:nil] start];
    }
}

- (void)read {
    pthread_rwlock_rdlock(&_lock);
    
    sleep(1);
    NSLog(@"*****read******");
    
    pthread_rwlock_unlock(&_lock);
}

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


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

@end

3、异步栅栏函数使用dispatch_barrier_async

#import "dispatchBarrierVC.h"

@interface dispatchBarrierVC ()
@property (strong, nonatomic) dispatch_queue_t queue;
@end

@implementation dispatchBarrierVC

- (void)viewDidLoad {
   [super viewDidLoad];
   self.queue = dispatch_queue_create("queue", DISPATCH_QUEUE_CONCURRENT);
   
   for (int i = 0; i < 10; i++) {
       [[[NSThread alloc] initWithTarget:self selector:@selector(read) object:nil] start];
       [[[NSThread alloc] initWithTarget:self selector:@selector(write) object:nil] start];
   }
}

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

- (void)write {
   dispatch_barrier_async(self.queue, ^{ // 这个函数，会用栅栏保护起来，保证只是单线程访问
       sleep(1);
       NSLog(@"-----------write-----------");
   });
   
}

@end