Unix系统编程_cha11.6_线程同步

#include <stdio.h>
#include <pthread.h>
#include <stdlib.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;
int f_id;
};

struct foo *foo_alloc(void){
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){
pthread_mutex_lock(&hashlock);
fp->f_count++;
pthread_mutex_unlock(&hashlock);
}

struct foo *foo_find(int id){
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_release(struct foo *fp){
struct foo *tfp;
int idx;

pthread_mutex_lock(&hashlock);
if(--fp->f_count == 0){
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);
}
}

int main(void)
{
printf("Hello World!\n");
return 0;
}