线程共享全局变量和私有全局变量

共享全局变量实例：

#include <stdio.h>
#include <pthread.h>
#include <unistd.h>
#include <stdlib.h>
int key=100;
void *helloworld_one(char *argc)
{
    printf("the message is %s\n",argc);
    key=10;
    printf("key=%d, the child is %u\n",key,pthread_self());
    return 0;
}

void *helloworld_two(char *argc)
{
    printf("the message is %s\n",argc);
    sleep(1);
    printf("key=%d, the child is %u\n",key,pthread_self());
}

int main()
{
    pthread_t thread_id_one;
    pthread_t thread_id_two;
    pthread_create(&thread_id_one,NULL,helloworld_one,"helloworld");
    pthread_create(&thread_id_two,NULL,helloworld_two,"helloworld");
    pthread_join(thread_id_one,NULL);
    pthread_join(thread_id_two,NULL);
    return 0;
}

#include <stdio.h>
#include <pthread.h>
pthread_key_t key;

void echomsg(void *t)
{
    printf("destructor excuted in thread %u, param=%u\n",pthread_self(),(int *)t);
}

void *child1(void *arg)
{
    int i=10;
    int tid=pthread_self();
    printf("\nset key value %d in thread %u\n",i,tid);
    pthread_setspecific(key,&i);
    printf("thread one sleep 2 until thread two finish\n");
    sleep(2);
    printf("\nthread %u returns %d, add is %u\n",tid,*(int *)pthread_getspecific(key),(int *)pthread_getspecific(key));

}

void *child2(void *arg)
{
    int temp=20;
    int tid=pthread_self();
    printf("\nset key value %d in thread %u\n",temp,tid);
    pthread_setspecific(key,&temp);
    sleep(1);
    printf("thread %u returns %d,add is %u\n",tid,*(int *)pthread_getspecific(key),(int *)pthread_getspecific(key));
}

int main()
{
    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;
}

从运行结果来看，各线程对自己的私有数据操作互相不影响，虽然同名全局，但访问的内存空间并不是同一个。