[C++知识库]【无标题】

实验17

1

#include <stdio.h>
#include <sys/types.h>
#include <unistd.h>
#include <stdlib.h>
int main()
{
	pid_t pid;
	char*msg;
	int k;
	printf("观察父子进程执行的先后顺序，了解调度算法的特征\n");
	pid=fork();
	switch(pid) {
		case 0:
		msg="子进程在运行";
		k=3;
		break;
		case -1:
		msg="进程创建失败";
		break;
		default:
		msg="父进程在运行";
		k=5;
		break;
	}
	while(k>0)
	{
	puts(msg);
	sleep(1);
	k--; }
	exit(0);
}

2

并发程序-父子进程线程异步性

#include <stdio.h>
#include <pthread.h>
static int run=1;
static int retvalue;
void *threadfunc(void*arg) {
	int*running=arg;
	printf("子线程初始化完毕，传入参数为：
	%d\n",*running);
	while(*running)
	{
		printf("子线程正在运行\n");
		usleep(1);
	}
	printf("子线程退出\n");
	retvalue=8;
	pthread_exit((void*)&retvalue);
}
int main()
{
	pthread_t pt;
	int ret=-1;
	int times=3;
	int i=0;
	int *ret_join=NULL;
	ret=pthread_create(&pt,NULL,(void*)threadfun
	c,&run);
	if(ret!=0)
	{
		printf("建立线程失败\n");
		return 1;
	}
	printf("主线程创建子线程后在运行...\n");
	usleep(1);
	printf("主线程调用usleep(1)...\n");
	for(;i<times;i++)
	{
		printf("主线程打印i=%d\n",i);
		usleep(1);
	}
	run=0;
	pthread_join(pt,(void*)&ret_join);
	printf("线程返回值为：%d\n",*ret_join);
	return 0;
}

编译：
gcc thread.c -o thread -lpthread
运行：
./thread

3

多线程对共享变量的非互斥访问

#include <stdio.h>
#include <stdlib.h>
#include <pthread.h>
#include <unistd.h>
#include <string.h>
int num=30,count=10;
void *sub1(void *arg) {
	int i = 0,tmp;
	for (; i <count; i++)
	{
		tmp=num-1;
		usleep(13);
		num=tmp;
		printf("线程1 num减1后值为: %d\n",num);
	}
	return ((void *)0);
}
void *sub2(void *arg){
	int i=0,tmp;
	for(;i<count;i++)
	{
		tmp=num-1;
		usleep(31);
		num=tmp;
		printf("线程2 num减1后值为: %d\n",num);
	}
	return ((void *)0);
}
int main(int argc, char** argv) {
	pthread_t tid1,tid2;
	int err,i=0,tmp;
	void *tret;
	err=pthread_create(&tid1,NULL,sub1,NULL);
	if(err!=0)
	{
		printf("pthread_create
		error:%s\n",strerror(err));
		exit(-1);
	}
	err=pthread_create(&tid2,NULL,sub2,NULL);
	if(err!=0)
	{
		printf("pthread_create
		error:%s\n",strerror(err));
		exit(-1);
	}
	for(;i<count;i++)
	{
		tmp=num-1;
		usleep(5);
		num=tmp;
		printf("main num减1后值为: %d\n",num);
	}
	printf("两个线程运行结束\n");
	err=pthread_join(tid1,&tret);
	if(err!=0)
	{
		printf("can not join with 
		thread1:%s\n",strerror(err));
		exit(-1);
	}
	printf("thread 1 exit code %d\n",(int)tret);
	err=pthread_join(tid2,&tret);
	if(err!=0)
	{
		printf("can not join with 
		thread1:%s\n",strerror(err));
		exit(-1);
	}
	printf("thread 2 exit code %d\n",(int)tret);
	return 0;
}