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! ");
    return 0;
}