{解决}读写锁，写锁呗读锁阻塞了

o_unix

大家好，我想测试读写锁，写线程一直不能获得锁，而是读线程一直占据着，代码如下：

1. 
   
2. #include <stdio.h>
   
3. #include <stdlib.h>
   
4. #include <unistd.h>
   
5. #include <pthread.h>
   
6. 
   
7. #define size 10
   
8. int i = 0;
   
9. pthread_rwlock_t rwlock;
   
10. 
    
11. void *read_func( void *arg);
    
12. void *write_func( void *arg);
    
13. 
    
14. int main( void)
    
15. {
    
16. int j = 2*size;
    
17. pthread_t *tids = (pthread_t *)malloc( j*sizeof( pthread_t));
    
18. pthread_rwlockattr_t rwlockattr;
    
19. pthread_rwlockattr_init( &rwlockattr);
    
20. pthread_rwlockattr_setkind_np (&rwlockattr, PTHREAD_RWLOCK_PREFER_WRITER_NONRECURSIVE_NP);
    
21. pthread_rwlock_init( &rwlock, NULL);
    
22. int m = 0;
    
23. 
    
24. for( m =0; m < j; m++)
    
25. {
    
26. if( m < size)
    
27. {
    
28. pthread_create( tids+m, NULL, write_func, (void*)m);
    
29. }
    
30. else
    
31. {
    
32. pthread_create( tids+m, NULL, read_func, (void *)m);
    
33. }
    
34. }
    
35. 
    
36. 
    
37. for( m = 0; m < j; m++)
    
38. {
    
39. pthread_join( *(tids+m), (void *)0);
    
40. }
    
41. pthread_rwlock_destroy( &rwlock);
    
42. return 0;
    
43. }
    
44. 
    
45. void * read_func( void *arg)
    
46. {
    
47. while( i < 10)
    
48. {
    
49. pthread_rwlock_rdlock( &rwlock);
    
50. printf("%d reading i:%d\n", (int)arg, i);
    
51. pthread_rwlock_unlock( &rwlock);
    
52. }
    
53. void *write_func( void *arg)
    
54. {
    
55. pthread_rwlock_wrlock( &rwlock);
    
56. printf("%d read i: %d\n", (int)arg, i++);
    
57. printf("%d writing i: %d\n", (int)arg, i);
    
58. pthread_rwlock_unlock( &rwlock);
    
59. }
    
60.                                        
    

复制代码

我查看锁的状态的发现：
(gdb) print rwlock
$13 = {__data = {__lock = 0, __nr_readers = 10,
    __readers_wakeup = 0, __writer_wakeup = 0,
    __nr_readers_queued = 0, __nr_writers_queued = 10,
    __writer = 0, __pad1 = 0, __pad2 = 0, __pad3 = 0,
    __flags = 0},
  __size = "\000\000\000\000\n", '\0' <repeats 15 times>, "\n", '\0' <repeats 34 times>, __align = 42949672960}

写线程已经在排队了，为什么写线程不能获得锁呢？写锁的优先级不是比读锁高吗？
测试过程中读锁可以抢占写锁，没有出现写锁抢占读锁的情况，请大家给看看我那里理解所了，谢谢先。

o_unix

果然默认是读优先的。现在是写优先的了