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关于互斥量《APUE》

时间：2010-07-05

来源：互联网

本帖最后由 blackgenius 于 2010-07-05 18:08 编辑

CU的高手们，请指教一下APUE里面的一段关于互斥量的程序，本人菜鸟，无法理解，请求指点：
其中有两句，真不知道什么意思，
fp->f_next = fh[idx];
fh[idx] = fp->f_next;
请指点迷津

#include <stdlib.h>
#include <pthread.h>
#define NHASH 29
#define HASH(fp) (((unsigned long)fp)%NHASH)
struct foo *fh[NHASH];
pthread_mutex_t hashlock = PTHREAD_MUTEX_INITIALIZER;
struct foo {
int f_count;
pthread_mutex_t f_lock;
struct foo *f_next; /* protected by hashlock */
int f_id;
/* ... more stuff here ... */
};
struct foo *
foo_alloc(void) /* allocate the object */
{
struct foo *fp;
int idx;
if ((fp = malloc(sizeof(struct foo))) != NULL) {
fp->f_count = 1;
if (pthread_mutex_init(&fp->f_lock, NULL) != 0) {
free(fp);
return(NULL);
}
idx = HASH(fp);
pthread_mutex_lock(&hashlock);
fp->f_next = fh[idx];
fh[idx] = fp->f_next;
pthread_mutex_lock(&fp->f_lock);
pthread_mutex_unlock(&hashlock);
/* ... continue initialization ... */
pthread_mutex_unlock(&fp->f_lock);
}
return(fp);
}
void
foo_hold(struct foo *fp) /* add a reference to the object */
{
pthread_mutex_lock(&fp->f_lock);
fp->f_count++;
pthread_mutex_unlock(&fp->f_lock);
}
struct foo *
foo_find(int id) /* find an existing object */
{
struct foo *fp;
int idx;
idx = HASH(fp);
pthread_mutex_lock(&hashlock);
for (fp = fh[idx]; fp != NULL; fp = fp->f_next) {
if (fp->f_id == id) {
foo_hold(fp);
break;
}
}
pthread_mutex_unlock(&hashlock);
return(fp);
}
void
foo_rele(struct foo *fp) /* release a reference to the object */
{
struct foo *tfp;
int idx;
pthread_mutex_lock(&fp->f_lock);
if (fp->f_count == 1) { /* last reference */
pthread_mutex_unlock(&fp->f_lock);
pthread_mutex_lock(&hashlock);
pthread_mutex_lock(&fp->f_lock);
/* need to recheck the condition */
if (fp->f_count != 1) {
fp->f_count--;
pthread_mutex_unlock(&fp->f_lock);
pthread_mutex_unlock(&hashlock);
return;
}
/* remove from list */
idx = HASH(fp);
tfp = fh[idx];
if (tfp == fp) {
fh[idx] = fp->f_next;
} else {
while (tfp->f_next != fp)
tfp = tfp->f_next;
tfp->f_next = fp->f_next;
}
pthread_mutex_unlock(&hashlock);
pthread_mutex_unlock(&fp->f_lock);
pthread_mutex_destroy(&fp->f_lock);
free(fp);
} else {
fp->f_count--;
pthread_mutex_unlock(&fp->f_lock);
}
}
105,1 底端

复制代码

作者: blackgenius 发布时间: 2010-07-05

fp->f_next = fh[idx];
fh[idx] = fp->f_next;
这个写错了,应为:
fp->f_next = fh[idx];
fh[idx] = fp;

另外,find那个算法也错了

作者: liwangli1983 发布时间: 2010-07-05

回复 liwangli1983
谢谢指点啊～我菜鸟一个，自己是没法发现这些错误的～

作者: blackgenius 发布时间: 2010-07-05

回复 liwangli1983

能帮忙解释下
         idx = HASH(fp);

            pthread_mutex_lock(&hashlock);

            fp->f_next = fh[idx];

            fh[idx] = fp;

            pthread_mutex_lock(&fp->f_lock);

            pthread_mutex_unlock(&hashlock);

            /* ... continue initialization ... */

            pthread_mutex_unlock(&fp->f_lock);
这段代码是什么意思？谢谢啦啊

作者: 单眼皮大姐发布时间: 2010-07-05

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