一.使用GCD实现多读单写
1.dispatch_barrier_async
dispatch_barrier_sync()或者dispatch_barrier_async()入队的block,会等到所有的之前入队的block执行完成后才开始执行。在barrier block后面入队的所有的block，会等到到barrier block本身已经执行完成之后才继续执行。
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dispatch_barrier 是一个类似于dispatch_async()/dispatch_sync()的API，它可以将barrier block提交到队列中，barrier block 只有提交到自定义的并发队列中才能真正的当做一个栅栏,它在这里起到一个承上启下的作用，只有比它（barrier block）先提交到自定义并发队列的block全部执行完成，它才会去执行，等它执行完成，在它之后添加的block才会继续往下执行。
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当dipatch_barrier block没有被提交到自定义的串行队列中，它与dispatch_async()/dispatch_sync()的作用是一样的。
场景需求：需要异步完成三个任务。任务一、任务二、任务三。要求：任务三必须在任务一、任务二完成之后触发。这就需要使用dispatch_barrier_async。
特点：像一堵围墙、成为任务的分割线。
dispatch_queue_t queue = dispatch_queue_create("myQueue", DISPATCH_QUEUE_CONCURRENT);
dispatch_async(queue, ^{
//任务1
for (int i = 0; i < 2; i++) {
NSLog(@"我是任务一、来自线程：%@",[NSThread currentThread]);
}
});
dispatch_async(queue, ^{
//任务2
for (int i = 0; i < 2 ; i++) {
NSLog(@"我是任务二、来自线程：%@",[NSThread currentThread]);
}
});
dispatch_barrier_async(queue, ^{
//栅栏
for (int i = 0; i < 1 ; i++) {
NSLog(@"我是分割线、来自线程：%@",[NSThread currentThread]);
}
});
dispatch_async(queue, ^{
//任务3
for (int i = 0; i < 1 ; i++) {
NSLog(@"我是任务三、来自线程：%@",[NSThread currentThread]);
}
});
2.使用dispatch_barrier_async实现多读单写锁
- (void)test2{
// 这里必须的自定义的并发队列，不能使用全局并发队列，或者串行队列
self.queue = dispatch_queue_create("my_quene", DISPATCH_QUEUE_CONCURRENT);
for (int i = 0; i < 10; i++) {
dispatch_async(self.queue, ^{
[self read];
});
dispatch_async(self.queue, ^{
[self read];
});
dispatch_async(self.queue, ^{
[self read];
});
dispatch_barrier_async(self.queue, ^{
[self write];
});
}
}
- (void)read {
NSLog(@"read");
}
- (void)write
{
NSLog(@"write");
}
一.使用pthread_rwlock_t实现多读单写
#import "ViewController.h"
#import <pthread.h>
@interface ViewController ()
@property (assign, nonatomic) pthread_rwlock_t lock;
@end
@implementation ViewController
- (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);
NSLog(@"read");
pthread_rwlock_unlock(&_lock);
}
- (void)write
{
pthread_rwlock_wrlock(&_lock);
NSLog(@"write");
pthread_rwlock_unlock(&_lock);
}
- (void)dealloc
{
pthread_rwlock_destroy(&_lock);
}
@end
- pthread_rwlock_rdlock 读取锁
- pthread_rwlock_wrlock 写入锁
- pthread_rwlock_destroy 销毁锁
