运行3个儿童过程

Running 3 child processes

本文关键字：过程 3个 运行      更新时间：2023-10-16

我有三个子过程和一个父母。

我希望该程序以该顺序运行[child1 then child2 tht Child3然后parent]。

我一直在尝试使用follwing代码，但它不给我正确的顺序！

代码：

#include<iostream>
#include<string.h>
#include<fstream>
#include<cstdlib>
#include <sys/types.h>
#include <sys/wait.h>
using namespace std;
int main()
{
    pid_t ch11;
    pid_t ch22;
    pid_t ch33;
    int ch1 = fork();
    int ch2 = fork();
    int ch3 = fork();

    if (ch1==0) //child1
    {    cout<<"this is child 1nGoing from 1 to child 2 ...nn";
        exit(0);
    }
    else if ( ch2==0)
    {    waitpid(ch11,0,0);
        cout<<"This is child 2nGoing from 2 To Child 3 ...nn";
        exit(0);
    }
    else if (ch3==0)
    {    waitpid(ch22,0,0);
        cout<<"This is child 3nFineshed !! going from 3 to parentnn";
        exit(0);
    }
    else
    {    waitpid(ch33,0,0);
        cout<<"This is parent , waited the whole childes to finish !!nn";
        exit(0);
    }
    return 0 ;
}

输出：

ubuntu@ubuntu-desktop:~$ c++ a.cpp -o p1
ubuntu@ubuntu-desktop:~$ ./p1
This is child 2
Going from 2 To Child 3 ...
this is child 1
Going from 1 to child 2 ...
this is child 1
Going from 1 to child 2 ...
this is child 1
Going from 1 to child 2 ...
This is child 2
Going from 2 To Child 3 ...
This is child 3
Fineshed !! going from 3 to parent
this is child 1
Going from 1 to child 2 ...
This is parent , waited the whole childs to finish.

我知道它将通过使用waitpid()函数来解决，我认为我使用waitpid()错误。

这是您代码的更好的仪器版本；它在输出中包括PID，并且输出为一条线。

#include <iostream>
#include <cstdlib>
#include <sys/wait.h>
#include <unistd.h>
using namespace std;
int main()
{
    int ch1 = fork();
    int ch2 = fork();
    int ch3 = fork();
    if (ch1 == 0) // child1
    {
        cout << (int)getpid() << ": This is child 1 - Finishedn";
        exit(0);
    }
    else if (ch2 == 0)
    {
        waitpid(ch1, 0, 0);
        cout << (int)getpid() << ": This is child 2 - Finishedn";
        exit(0);
    }
    else if (ch3 == 0)
    {
        waitpid(ch2, 0, 0);
        cout << (int)getpid() << ": This is child 3 - Finished!n";
        exit(0);
    }
    else
    {
        waitpid(ch3, 0, 0);
        cout << (int)getpid() << ": This is parent - waited for all children to finish!n";
        exit(0);
    }
    return 0;
}

样本输出：

$ ./3kids
40287: This is child 3 - Finished!
40285: This is child 1 - Finished
40286: This is child 2 - Finished
40290: This is child 1 - Finished
40289: This is child 2 - Finished
40288: This is child 1 - Finished
40284: This is parent - waited for all children to finish!
40291: This is child 1 - Finished
$

您可以看到，有一个过程认为自己是孩子3，两个过程认为自己是孩子2，而四个认为自己是孩子1的过程和一个认为自己是父母的过程。这与创建8个过程的不受约束的分叉一致。

只有3个孩子，要等待每个孩子，您需要更多的代码：

#include <iostream>
#include <cstdlib>
#include <sys/wait.h>
#include <unistd.h>
using namespace std;
void child(int n)
{
    flush(cout);        // No pending output
    int pid = fork();
    if (pid < 0)
        cerr << (int)getpid() << ": failed to forkn";
    else if (pid == 0)
    {
        cout << (int)getpid() << ": This is child " << n << " - Finishedn";
        exit(0);
    }
    else
    {
        int corpse;
        int status;
        while ((corpse = wait(&status)) != -1)
            cout << (int)getpid() << ": PID " << corpse << " exited with status "
                 << status << "n";
    }
}
int main()
{
    child(1);
    child(2);
    child(3);
    cout << (int)getpid() << ": This is parent - waited for all children to finish!n";
    return 0;
}

样本输出：

$ ./3kids
40336: This is child 1 - Finished
40335: PID 40336 exited with status 0
40337: This is child 2 - Finished
40335: PID 40337 exited with status 0
40338: This is child 3 - Finished
40335: PID 40338 exited with status 0
40335: This is parent - waited for all children to finish!
$

尽管您的评论"代码正在起作用，但它给了我错误的执行顺序。因此，我将在这里尝试。

int main()
{
    pid_t ch11;
    pid_t ch22;
    pid_t ch33;

这些变量的目的是什么？

    int ch1 = fork();

您阅读了叉式手册吗？它清楚地指出，何时创建子过程，它将在子女中返回0，并在父母中返回PID。它也可能失败，因此您应该检查过。

考虑到这一点.... 

    int ch2 = fork();

孩子和父都到达此行。因此，以前创建的儿童 forks以及。

    int ch3 = fork();

猜猜是什么。

    if (ch1==0) //child1
    {    cout<<"this is child 1nGoing from 1 to child 2 ...nn";

除非您不是（见下文）。

        exit(0);

应该是_exit。

    }
    else if ( ch2==0)
    {    waitpid(ch11,0,0);

什么？CH11甚至都不是初始化的，那么这应该做什么？您是否启用了警告来编译代码？

一般而言，我不知道您是否想制作 rickid 叉，从而创建了与父母关系的过程链，或者您想要同一父母的3个孩子过程。如果后者这是不好的，那么，如果前者这是更不错的，因为您将无法等待这样的过程。

[snip the rest]

最后，让我们地址

执行的错误序列

什么？

无法保证您的流程执行顺序。实际部

鉴于到目前为止所显示的内容，我倾向于猜测您要么误解了您的作业作业，要么"不常见"。无论哪种方式，我都强烈建议您说明应该用您的代码解决的实际问题。

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