关于Linux线程的一些小测试(1)

代码1

#include <stdio.h>
#include <stdlib.h>
#include <pthread.h>
int a=0;
void thr(void)
{
    while(a<1010)
    {
	    printf("this is a pthread %d \n",a++);
        //sleep(1);
    }
}
int main()
{
	pthread_t id;
	int i,ret;
	ret=pthread_create(&id,NULL,(void *)thr,NULL);
	if (ret)
	{
		printf("create pthread filed\n");
		exit(1);
	}
	printf("%s\n","this is main thread");
        printf("%s\n","i am waiting for sub thread join");
        a+=1000;
	pthread_join(id,NULL);
	printf("%s\n","sub thread returned");
	return 0;
}		

某一次运行的结果是

this is main thread
i am waiting for sub thread join
this is a pthread 0 
this is a pthread 1001 
this is a pthread 1002 
this is a pthread 1003 
this is a pthread 1004 
this is a pthread 1005 
this is a pthread 1006 
this is a pthread 1007 
this is a pthread 1008 
this is a pthread 1009 
sub thread returned

另外一次运行的结果是

this is main thread
this is a pthread 0 
this is a pthread 1 
this is a pthread 2 
i am waiting for sub thread join
this is a pthread 3 
this is a pthread 1004 
this is a pthread 1005 
this is a pthread 1006 
this is a pthread 1007 
this is a pthread 1008 
this is a pthread 1009 
sub thread returned