第10章 线程控制（3）_线程私有数据

#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>
#include <memory.h>

/*演示如何使用线程私有数据*/

pthread_key_t key;        //创建关联键，key本身可被多个线程共享，但其关联的私有数据却为线程独享
pthread_mutex_t key_mutex = PTHREAD_MUTEX_INITIALIZER;
int key_count = 3; //表示正在使用key的线程数量，初始化为3

//必须初始化为PTHREAD_ONCE_INT。
static pthread_once_t init_done = PTHREAD_ONCE_INIT;

//定义线程私有数据类型
typedef struct
{
    pthread_t thread_id;
    char* name; //线程名称
}private_t;


//析构函数
void destructor(void* arg)
{
    private_t* pv = (private_t*)arg;

    printf("thread \"%s\"(0x%lx) exit and free thread private data...\n", pv->name, pv->thread_id);
    free(arg);

    //判断是否删除key
    pthread_mutex_lock(&key_mutex);

    key_count--;
    if(key_count <=0){
        //当没有线程正在使用key时，则删除之。
        if(pthread_key_delete(key) != 0){
            perror("delete key error");
        }
        printf("key deleted!\n");
    }

    pthread_mutex_unlock(&key_mutex);   
}

//线程的初始化（用于安全创建关联键）
void thread_init(void)
{
   printf("key creating...\n");
   pthread_key_create(&key, destructor);
}

//获取线程私有数据
void* get_private(void)
{
    void* value = NULL;

    //获取私有数据
    value = pthread_getspecific(key);
    if(value == NULL){//还未关联
        value =malloc(sizeof(private_t));
        if(value == NULL){
            perror("Allock key value");
        }

        //设置关联
        if( pthread_setspecific(key, (void*)value) !=0){
            printf("pthread_setspecific error");
        }
    }

    return value;
}

//线程函数
void* th_rtn(void* arg)
{
    pthread_once(&init_done, thread_init);//多线程中thread_init只会被调用一次，从而保证
                                          //key只会被pthread_key_create创建一次。

    private_t* value = (private_t*)get_private();
    value->thread_id = pthread_self();
    value->name = (char*)arg;

    printf("thread \"%s\"(0x%lx) starting...\n", value->name, value->thread_id);

    sleep(1);

    return (void*)NULL;
}

int main(void)
{
    pthread_t  th1, th2, th3;

    int err = 0;
    //创建3个子线程，会对全局共享的key进行操作
    if((err = pthread_create(&th1, NULL, th_rtn, "Thread 1"))!=0){
        perror("pthread create error");
    }
    if((err = pthread_create(&th2, NULL, th_rtn, "Thread 2"))!=0){
        perror("pthread create error");
    }
    if((err = pthread_create(&th3, NULL, th_rtn, "Thread 3"))!=0){
        perror("pthread create error");
    }

    //等待子线程结束
    pthread_join(th1, NULL);
    pthread_join(th2, NULL);
    pthread_join(th3, NULL);

    return 0;
}
/*输出结果
 key creating...
 thread "Thread 3"(0xb62ffb70) starting...
 thread "Thread 2"(0xb6d00b70) starting...
 thread "Thread 1"(0xb7701b70) starting...
 thread "Thread 3"(0xb62ffb70) exit and free thread private data...
 thread "Thread 2"(0xb6d00b70) exit and free thread private data...
 thread "Thread 1"(0xb7701b70) exit and free thread private data...
 key deleted!
 */