多线程

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

void *thread_function(void *arg);
int now_num = 1;
int main(){
int res;

pthread_t a_thread;
void *thread_result;

res = pthread_create(&a_thread,NULL,thread_function,(void *)0);

int count = 1;
while(count++ <20){
if(now_num == 1){
printf("1");
now_num = 2;
}else{
sleep(1);
}
}
//等待线程结束
res = pthread_join(a_thread, &thread_result);
}
void *thread_function(void *arg){
int count = 1;
while(count++ < 20){
if(now_num == 2){
printf("2");
now_num = 1;
}else{
sleep(1);
}
//可不加，主进程退出后 线程也都退出
pthread_exit("i'm exit!");
}