體驗mutex

liiinuuux發表於2014-03-19
Mutex
10g新加了mutex，替換部分latch的功能。
經過了解，原來mutex不是oracle自己發明的，而是作業系統的一個功能。既然不是oracle獨家的，那我也想體驗一下，於是就有了下面小程式。

struct foo *fh[NHASH]是一個典型的hash table，上面有幾個表頭，每個表頭下面掛著一個foo連結串列，每個連結串列最後一個節點的next又指回表頭。
操作的過程就是   hold（f_count++） -> 操作 ->釋放（f_count--或free）

main函式里，對f2節點故意只hold，不釋放，最後列印的時候可以看到f_count是2

點選(此處)摺疊或開啟

  1. #include <stdio.h>
  2. #include <stdlib.h>
  3. #include <pthread.h>
  4. #include <unistd.h>
  5. #include <string.h>

  7. #define NHASH 29
  8. #define HASH(fp) (((unsigned long)fp)%NHASH)

  10. struct foo *fh[NHASH];

  12. pthread_mutex_t hashlock = PTHREAD_MUTEX_INITIALIZER;

  14. struct foo
  15. {
  16.     int f_count;
  17.     pthread_mutex_t f_lock;
  18.     struct foo* f_next;
  19.     int f_id;
  20.     int f_value;
  21. };

  23. struct foo* foo_alloc(int id, int value)
  24. {
  25.     struct foo* fp = NULL;
  26.     struct foo* tmp = NULL;
  27.     int idx;
  28.     if((fp = malloc(sizeof(struct foo))) != NULL)
  29.     {
  30.         fp->f_count = 1;
  31.         if(pthread_mutex_init(&fp->f_lock, NULL) != 0)
  32.         {
  33.             free(fp);
  34.             return NULL;
  35.         }
  36.     }
  37.     
  38.     idx = HASH(fp);
  39.     pthread_mutex_lock(&hashlock);

  41.     if(fh[idx] == NULL)
  42.     {
  43.         fh[idx] = fp;
  44.     }
  45.     else
  46.     {
  47.         tmp = fh[idx];
  48.         while(tmp->f_next != NULL)
  49.         {
  50.             tmp = tmp->f_next;
  51.         }
  52.         tmp->f_next = fp;
  53.     }
  54.     fp->f_next = fh[idx];
  55.     pthread_mutex_lock(&fp->f_lock);
  56.     pthread_mutex_unlock(&hashlock);
  57.     fp->f_value = value;
  58.     fp->f_id = id;
  59.     pthread_mutex_unlock(&fp->f_lock);
  60.     return fp;
  61. }

  63. void foo_hold(struct foo* fp)
  64. {
  65.     pthread_mutex_lock(&fp->f_lock);
  66.     fp->f_count++;
  67.     pthread_mutex_unlock(&fp->f_lock);
  68. }

  70. struct foo* foo_find(int id)
  71. {
  72.     struct foo *fp;
  73.     int idx;
  74.     idx = HASH(fp);
  75.     pthread_mutex_lock(&hashlock);
  76.     for(fp=fh[idx]; fp!=NULL; fp=fp->f_next)
  77.     {
  78.         if(fp->f_id == id)
  79.         {
  80.             foo_hold(fp);
  81.             break;
  82.         }
  83.     }
  84.     pthread_mutex_unlock(&hashlock);
  85.     return(fp);
  86. }

  88. void foo_rele(struct foo* fp)
  89. {
  90.     struct foo* tfp;
  91.     int idx;
  92.     
  93.     pthread_mutex_lock(&fp->f_lock);
  94.     if(fp->f_count <= 1)
  95.     {
  96.         pthread_mutex_lock(&hashlock);
  97.         idx = HASH(fp);
  98.         tfp = fh[idx];
  99.         if (tfp == fp)
  100.         {
  101.             if(fp->f_next != fh[idx]) fh[idx] = fp->f_next;
  102.             else fh[idx] = NULL;
  103.         }
  104.         else
  105.         {
  106.             while(tfp->f_next != fp)
  107.             {
  108.                 tfp = tfp->f_next;
  109.             }
  110.             tfp->f_next = fp->f_next;
  111.         }
  112.         pthread_mutex_unlock(&hashlock);
  113.         pthread_mutex_unlock(&fp->f_lock);
  114.         pthread_mutex_destroy(&fp->f_lock);
  115.         free(fp);
  116.     }
  117.     else
  118.     {
  119.         fp->f_count--;
  120.         pthread_mutex_unlock(&fp->f_lock);
  121.     }
  122. }

  124. void main()
  125. {
  126.     struct foo* f1 = foo_alloc(1, 100);
  127.     struct foo* f2 = foo_alloc(2, 200);
  128.     
  129.     foo_hold(f1);
  130.     f1->f_value = 111;
  131.     foo_rele(f1);

  133.     foo_hold(f2);
  134.     f2->f_value = 222;

  136.     foo_rele(f1);

  138.     int i;
  139.     for(i=1; i<NHASH; i++)
  140.     {
  141.         if(fh[i] != NULL)
  142.         {
  143.             printf(\"fh[%d]: id=%d, value=%d, count=%d\\n\", i, fh[i]->f_id, fh[i]->f_value, fh[i]->f_count);
  144.         }
  145.     }

  147.     return;
  148. }

來自 “ ITPUB部落格 ” ，連結：http://blog.itpub.net/26239116/viewspace-1124827/，如需轉載，請註明出處，否則將追究法律責任。

相關文章