多线程锁的使用
2017-05-31 本文已影响29人
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方法一:用NSLock
TestObj *obj = [[TestObj alloc] init];
//线程1
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
[lock lock];
[obj method1];
sleep(30);
[lock unlock];
});
//线程2
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
sleep(5);//以保证让线程2的代码后执行
[lock lock];
[obj method2];
[lock unlock];
});
方法二:用@synchronized
TestObj *obj = [[TestObj alloc] init];
//线程1
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
@synchronized (obj) {
[obj method1];
}
sleep(30);
});
//线程2
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
sleep(5);//以保证让线程2的代码后执行
@synchronized (obj) {
[obj method2];
}
});
方法三:用GCD的dispatch_semaphore_t和dispatch_semaphore_wait
- dispatch_semaphore_create(num),这里的num相当于古代将军发的令牌数目,如果num是1,表示可以分配给一个将领去执行任务,实例代码代码如下:
dispatch_semaphore_t semaphore = dispatch_semaphore_create(1);
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
dispatch_semaphore_wait(semaphore, DISPATCH_TIME_FOREVER);
NSLog(@"method1");
sleep(10);
dispatch_semaphore_signal(semaphore);
});
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
sleep(1);
dispatch_semaphore_wait(semaphore, DISPATCH_TIME_FOREVER);
NSLog(@"method2");
dispatch_semaphore_signal(semaphore);
});
这里dispatch_semaphore_create(1)创建的是一个令牌,所以会先执行method1任务,然后等待10秒后发送一个信号(dispatch_semaphore_signal(semaphore)
)使信号量+1,再执行method2任务
- num如果是0,没有令牌,就立即执行dispatch_semaphore_wait方法:
dispatch_semaphore_t semaphore = dispatch_semaphore_create(0);
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
dispatch_semaphore_wait(semaphore, DISPATCH_TIME_FOREVER);
NSLog(@"method1");
sleep(10);
dispatch_semaphore_signal(semaphore);
});
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
sleep(1);
dispatch_semaphore_wait(semaphore, DISPATCH_TIME_FOREVER);
NSLog(@"method2");
dispatch_semaphore_signal(semaphore);
});
这里只执行到dispatch_semaphore_wait(semaphore, DISPATCH_TIME_FOREVER);
,永远不会执行NSLog(@"method1")
和下面的method2方法
- num如果是2,分配2个令牌,使得下面两个进程都可以执行:
dispatch_semaphore_t semaphore = dispatch_semaphore_create(2);
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
dispatch_semaphore_wait(semaphore, DISPATCH_TIME_FOREVER);
NSLog(@"method1");
sleep(10);
dispatch_semaphore_signal(semaphore);
});
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
sleep(1);
dispatch_semaphore_wait(semaphore, DISPATCH_TIME_FOREVER);
NSLog(@"method2");
dispatch_semaphore_signal(semaphore);
});
方法三:用pthread_mutex互斥锁
- 初始化
导入#import <pthread.h>
@interface XYThread ()
{
pthread_mutex_t mutex; //声明pthread_mutex_t的结构
}
@end
//在viewDidLoad里初始化
- (void)viewDidLoad {
[super viewDidLoad];
pthread_mutex_init(&mutex, NULL);
}
- 加锁and解锁
//加锁
pthread_mutex_lock(&mutex);
/*你的代码*/
//解锁
pthread_mutex_unlock(&mutex);
- 释放锁
- (void)dealloc{
pthread_mutex_destroy(&mutex); //释放该锁的数据结构
}
针对函数递归调用的情况,可以使用递归锁
- (void)viewDidLoad {
NSMutableArray *array = @[].mutableCopy;
pthread_mutexattr_t attr;
pthread_mutexattr_init(&attr);
pthread_mutexattr_settype(&attr, PTHREAD_MUTEX_NORMAL);//定义锁的类别
__block pthread_mutex_t mutex;
pthread_mutex_init(&mutex, &attr);
pthread_mutexattr_destroy (&attr);
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
pthread_mutex_lock(&mutex);
[array addObject:@"1"];
[NSThread sleepForTimeInterval:1];
NSLog(@"thread1");
pthread_mutex_unlock(&mutex);
});
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
pthread_mutex_lock(&mutex);
[array addObject:@"2"];
[NSThread sleepForTimeInterval:2];
NSLog(@"thread2");
pthread_mutex_unlock(&mutex);
});
}