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电梯直达

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发表于 2013-06-10 14:53 |只看该作者 |倒序浏览

原帖http://zhidao.baidu.com/question ... 6#answer-1400878524
用wait回收进程只有第一个返回了正确的pid其余的都是返回-1
而使用waitpid指定pid都正确返回？？

使用wait

#include<stdio.h>
#include<unistd.h>
#include<stdlib.h>
#include<errno.h>
int main()
{
pid_t pid2 = fork();
if(pid2 == 0)
{
//我是子进程p2，被P1 fork出的
printf("p2 pid:%d ppid%d\n",getpid(),getppid());
exit(0);
}
else
{
//我还是是父进程p1，我要fork出p3
pid_t pid3 = fork();
if(pid3 == 0)
{
printf("p3 pid:%d ppid%d\n",getpid(),getppid());
//父进程P3生成P4,P5,然后等p4,p5结束后生成p6
pid_t pid4 = fork();
if(pid4 == 0)
{
printf("p4 pid:%d ppid%d\n",getpid(),getppid());
//我是p4
exit(0);
}
else
{
//我是p3, 还要fork出p5
pid_t pid5 = fork();
if(pid5 == 0)
{
printf("p5 pid:%d ppid%d\n",getpid(),getppid());//我是p5
exit(0);
}
else
{
//我还是p3
printf("pid:%d finish\n",wait());
}
printf("pid:%d finish\n",wait());//wait(pid4);
}
//p4,p5结束，生成p6
pid_t pid6 = fork();
if(pid6 == 0)
{
printf("p6 pid:%d ppid%d\n",getpid(),getppid());
//我是p6
exit(0);
}
else
{
printf("pid:%d finish\n",wait());//wait(pid6);
}
exit(0);
}
else
{
//我是p1
printf("pid:%d finish\n",wait());//wait(pid2);//回收p2
printf("pid:%d finish\n",wait());//wait(pid3);//回收p3
}
sleep(1);
//p2,p3执行完,生成p7
pid_t pid7 = fork();
if(pid7 == 0)
{
printf("p7 pid:%d ppid%d\n",getpid(),getppid());
//我是p7
exit(0);
}
else
{
printf("pid:%d finish\n",wait());//wait(pid7);
}
}
getchar();
}

复制代码

运行结果
p2  pid:25401 ppid25400
p3  pid:25402 ppid25400
pid:25401 finish
p4  pid:25403 ppid25402
p5  pid:25404 ppid25402
pid:-1 finish
pid:-1 finish
p6  pid:25405 ppid25402
pid:-1 finish
pid:-1 finish
p7  pid:25408 ppid25400
pid:-1 finish

使用waitpid

#include<stdio.h>
#include<unistd.h>
#include<stdlib.h>
#include<errno.h>
int main()
{
pid_t pid2 = fork();
if(pid2 == 0)
{
//我是子进程p2，被P1 fork出的
printf("p2 pid:%d ppid%d\n",getpid(),getppid());
exit(0);
}
else
{
//我还是是父进程p1，我要fork出p3
pid_t pid3 = fork();
if(pid3 == 0)
{
printf("p3 pid:%d ppid%d\n",getpid(),getppid());
//父进程P3生成P4,P5,然后等p4,p5结束后生成p6
pid_t pid4 = fork();
if(pid4 == 0)
{
printf("p4 pid:%d ppid%d\n",getpid(),getppid());
//我是p4
exit(0);
}
else
{
//我是p3, 还要fork出p5
pid_t pid5 = fork();
if(pid5 == 0)
{
printf("p5 pid:%d ppid%d\n",getpid(),getppid());//我是p5
exit(0);
}
else
{
//我还是p3
printf("pid:%d finish\n",waitpid(pid5,NULL,0));
}
printf("pid:%d finish\n",waitpid(pid4,NULL,0));//wait(pid4);
}
//p4,p5结束，生成p6
pid_t pid6 = fork();
if(pid6 == 0)
{
printf("p6 pid:%d ppid%d\n",getpid(),getppid());
//我是p6
exit(0);
}
else
{
printf("pid:%d finish\n",waitpid(pid6,NULL,0));//wait(pid6);
}
exit(0);
}
else
{
//我是p1
printf("pid:%d finish\n",waitpid(pid2,NULL,0));//wait(pid2);//回收p2
printf("pid:%d finish\n",waitpid(pid3,NULL,0));//wait(pid3);//回收p3
}
//sleep(1);
//p2,p3执行完,生成p7
pid_t pid7 = fork();
if(pid7 == 0)
{
printf("p7 pid:%d ppid%d\n",getpid(),getppid());
//我是p7
exit(0);
}
else
{
printf("pid:%d finish\n",waitpid(pid7,NULL,0));//wait(pid7);
}
}
getchar();
}

复制代码

运行结果
p2  pid:25606 ppid25605
p3  pid:25607 ppid25605
pid:25606 finish
p4  pid:25608 ppid25607
p5  pid:25609 ppid25607
pid:25609 finish
pid:25608 finish
p6  pid:25610 ppid25607
pid:25610 finish
pid:25607 finish
p7  pid:25611 ppid25605
pid:25611 finish