APUE figure 11.12 勘误 关于死锁解决办法的代码错误

虽然我自己很不愿意面对这个事实。。。但是它就是错了，完全解释不通

我把书中问题代码的源码放在blog最后，并和第三版APUE进行比较

比较可以发现第二版中有这样一段代码和第三不一样

第二版foo_find里面：

foo_find(int id) /* find a existing object */
{
struct foo  *fp;
int         idx;
idx = HASH(fp);
pthread_mutex_lock(&hashlock);
for (fp = fh[idx]; fp != NULL; fp = fp->f_next) {

很明显的可以看出局部变量fp是没有初始化的第一次使用fp是在

idx = HASH(fp) 那么这个时候fp就是未定义的垃圾值，这么做显然是错误的

我在第三版里面看到的就不一样了

struct foo *
foo_find(int id) /* find an existing object */
{
struct foo *fp;
pthread_mutex_lock(&hashlock);
for (fp = fh[HASH(id)]; fp != NULL; fp = fp->f_next) {

利用id 检索哈希列表并给fp赋值定义和赋有意义值之间并没有使用fp，符合程序设计意义

所以我觉得第二版这里就明显的错了。可能是作者这里只是概念性的给出解决方案，没有具体的做代码测试。书中并没有写出带main函数的测试代码。我写的blog笔记也一直在弥补这个遗憾，把很多作者没有写出测试的代码都测试一遍。尽量给出每个API的demo

APUE 第二版 figure11.12的源码：

#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; /* protected by hashlock */
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 ... */
}
return(fp);
}
void
foo_hold(struct foo *fp) /* add a reference to the object */
{
pthread_mutex_lock(&hashlock);
fp->f_count++;
pthread_mutex_unlock(&hashlock);
}
struct foo *
foo_find(int id) /* find a 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) {
fp->f_count++;
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(&hashlock);
if (--fp->f_count == 0) { /* last reference, 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_destroy(&fp->f_lock);
free(fp);
} else {
pthread_mutex_unlock(&hashlock);
}
}


第三版源码

#include <stdlib.h>
#include <pthread.h>
#define NHASH 29
#define HASH(id) (((unsigned long)id)%NHASH)
struct foo *fh[NHASH];
pthread_mutex_t hashlock = PTHREAD_MUTEX_INITIALIZER;
struct foo {
int  f_count; /* protected by hashlock */
pthread_mutex_t f_lock;
int  f_id;
struct foo *f_next; /* protected by hashlock */
/* ... more stuff here ... */
};

struct foo *
foo_alloc(int id) /* allocate the object */
{
struct foo *fp;
int  idx;
if ((fp = malloc(sizeof(struct foo))) != NULL) {
fp->f_count = 1;
fp->f_id = id;
if (pthread_mutex_init(&fp->f_lock, NULL) != 0) {
free(fp);
return(NULL);
}
idx = HASH(id);
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);
}
return(fp);
}

void
foo_hold(struct foo *fp) /* add a reference to the object */
{
pthread_mutex_lock(&hashlock);
fp->f_count++;
pthread_mutex_unlock(&hashlock);
}

struct foo *
foo_find(int id) /* find an existing object */
{
struct foo *fp;
pthread_mutex_lock(&hashlock);
for (fp = fh[HASH(id)]; fp != NULL; fp = fp->f_next) {
if (fp->f_id == id) {
fp->f_count++;
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(&hashlock);
if (--fp->f_count == 0) { /* last reference, remove from list */
idx = HASH(fp->f_id);
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_destroy(&fp->f_lock);
free(fp);
}else {
pthread_mutex_unlock(&hashlock);
}
}

如有错漏，欢迎交流指正。Thank you