四：线程私有数据 pthread_key_create（七）

    全局变量可以多个函数间共享数据，全局变量可以所有线程共有。
    但有时，需要提供线程私有的全局变量，仅在某个线程中有效。 
    线程私有数据 TSD thread-specific Data

    typedef int pthread_key_t
    该函数从TSD池中分配一项，将其地址值赋给 key 供以后访问使用，如果第二个参数不为空，在线程退出时(pthread_exit)将以 key 为所关联的数据为参数调用指向的函数，以释放分配的缓冲区
int pthread_key_create(pthread_key_t *key, viod(*deser_funciton) (void *))

注销一个TSD
int pthread_key_delete(pthread_key_t key)

读写线程私有数据

int pthread_setspecific(pthread_key_t key,const void *pointer)

void *pthread_getspecific(pthread_key_t key)

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

pthread_key_t key; //typedef int pthread_key_t

void echomsg(void *t)      退出时执行
{                     //pthread_self() 返回 unsigned long  %lu
    printf("destructor excuted itn thread %lu,param=%p\n",pthread_self(),((int *)t));
}                                                 地址                          地址

void *child1(void *a)
{
    int i = 10; //临时变量 栈中
    unsigned long tid =pthread_self();
    printf("\nset key value %d in thread %lu\n",i,tid);

    pthread_setspecific(key,&i);  //key 全局变量

    printf("thread one sleep 2 until thread two finishe\n");//等待让另一个线程修改值
    sleep(2);
    printf("\nthread %lu retrun %d,add is %p\n",tid, *((int *)pthread_getspecific(key)), (int *)pthread_getspecific(key));  //打印当前线程中的值
  
地址  %p 地址
}

void *child2(void *b)
{
    int tmp = 20;
    unsigned long tid = pthread_self();
    printf("\nset key value %d in thread %lu\n",tmp,tid);

    pthread_setspecific(key,&tmp);  //key 全局变量
    sleep(1);

    printf("\nthread %lu retrun %d,add is %p\n",tid, *((int *)pthread_getspecific(key)), (int *)pthread_getspecific(key));  //打印当前线程中的值
}

int main(void)
{
    pthread_t tid1,  tid2;

    pthread_key_create(&key, echomsg);

    pthread_create(&tid1, NULL, (void *)*child1, NULL);
    pthread_create(&tid2, NULL, (void *)*child2, NULL);

    pthread_join(tid1, NULL);
    pthread_join(tid2, NULL);

    return 0;
}

ywx@yuweixian:~/yu/professional/4$ ./pthread_key

set key value 20 in thread 3070704496

set key value 10 in thread 3079097200
thread one sleep 2 until thread two finishe

thread 3070704496 retrun 20,add is 0xb707338c
destructor excuted itn thread 3070704496,param=0xb707338c

thread 3079097200 retrun 10,add is 0xb787438c
destructor excuted itn thread 3079097200,param=0xb787438c