c - 有没有办法更好地路由流程？

Question

我尝试使用 fork() 创建进程树，以便每个父进程的子进程数在给定数组中，例如，如果数组是 {2,1,3,0,0,0,0}树看起来像这样:

                |   a   |
                /       \
             | b |     |  c  |
             /         /  |  \                 
          | d |   | e | | f | | g |

通过检查 fork() 返回的值是否为 0，我能够创建进程并将父进程与子进程分开。我设法创建了一个流程树，但我设法创建的树是对称的，而不是我真正想要构建的。 sibling 之间的路由过程我想不通，

我如何分别检查每个进程应该为它创建多少子进程，以及在不为其他同级进程创建的情况下为它创建？

这是我到目前为止得到的:

int main() {
    int nums[7] = { 2,1,3,0,0,0,0 };
    int pid, pid2;
    size_t len = sizeof(nums)/sizeof(int);
    int childs2;
        printf("\nProcess number %d has pid= %d\n", 0, getpid());
        int childs = 1;
        while( childs <= nums[0] ) {
            pid = fork();
            if (pid == 0 ) {
                printf("Process number %d has pid= %d\n", childs, getpid());
                printf("I am Process with pid=%d and my parent pid=%d\n", getpid(), getppid());
                waitpid(getppid());
                for (int i=1; i<len; i++) {
                    childs2 = 0;
                    if (childs2 < nums[i]) {
                        pid2 = fork();
                        if (pid2 == 0) {
                            printf("Process number %d has pid= %d\n", childs, getpid());
                            printf("I am Process with pid=%d and my parent pid=%d\n", getpid(), getppid());
                            waitpid(getppid());
                            break;
                        } else {
                            wait(NULL);
                            childs2++;
                        }
                    } else {
                        childs2++;
                    }
                }
                break;
            } else {
            wait(NULL);
            childs++;
            }
        }
    return 0;
}

我必须区分进程才能知道哪个进程是叶进程，哪个进程是父进程。为此，我需要在每个过程中执行不同的操作，但我想不出办法，

我的输出是:

Process number 0 has pid= 98431
Process number 1 has pid= 98432
I am Process with pid=98432 and my parent pid=98431
Process number 1 has pid= 98433
I am Process with pid=98433 and my parent pid=98432
Process number 1 has pid= 98434
I am Process with pid=98434 and my parent pid=98432
Process number 2 has pid= 98435
I am Process with pid=98435 and my parent pid=98431
Process number 2 has pid= 98436
I am Process with pid=98436 and my parent pid=98435
Process number 2 has pid= 98437
I am Process with pid=98437 and my parent pid=98435

树看起来像:

                |   a   |
                /       \
             | b |      | c |
             /   \      /   \                 
          | d | | e || f | | g |

但我希望输出为:

Process number 0 has pid= 98431
Process number 1 has pid= 98432
I am Process with pid=98432 and my parent pid=98431
Process number 2 has pid= 98433
I am Process with pid=98433 and my parent pid=98431
Process number 3 has pid= 98434
I am Process with pid=98434 and my parent pid=98432
Process number 4 has pid= 98435
I am Process with pid=98435 and my parent pid=98433
Process number 5 has pid= 98436
I am Process with pid=98436 and my parent pid=98433
Process number 6 has pid= 98437
I am Process with pid=98437 and my parent pid=98433

所以树看起来像:

                |   a   |
                /       \
             | b |     |  c  |
             /         /  |  \                 
          | d |   | e | | f | | g | 

.

Answer 1

我们需要做的是跟踪我们在列表中的进程以及子进程在列表中的位置。以下代码显示了如何执行此操作。

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

#include <unistd.h>


#define NumberOf(a) (sizeof (a) / sizeof *(a))


/*  Create children for process p.

    In a child, return the number of that child process.
    In the parent, return -1.
*/
static int CreateChildren(int NumberOfChildren[], int FirstChild[], int p)
{
    //  Create children for process p.
    printf("Process %d has pid %u and parent %u.\n",
        p, (unsigned) getpid(), (unsigned) getppid());

    for (int i = 0; i < NumberOfChildren[p]; ++i)
    {
        pid_t pid = fork();
        if (pid == -1)
        {
            perror("fork");
            exit(EXIT_FAILURE);
        }
        if (pid == 0)
            /*  This is a child process, and it is child i of process p, so
                its process number is FirstChild[p] + i.  Return that.
            */
            return p = FirstChild[p] + i;
    }

    //  Wait for children to finish.
    for (int i = 0; i < NumberOfChildren[p]; ++i)
        wait(0);

    //  Tell caller the parent finished.
    return -1;
}


int main(void)
{
    int NumberOfChildren[] = { 2, 1, 3, 0, 0, 0, 0 };

    size_t N = NumberOf(NumberOfChildren);

    // Check the NumberOfChildren array for consistency.    
    {
        int sum = 0;
        for (size_t n = 0; n < N; ++n)
        {
            if (NumberOfChildren[n] < 0)
            {
                fprintf(stderr,
                    "Error, number of children cannot be negative but is %d.\n",
                    NumberOfChildren[n]);
                exit(EXIT_FAILURE);
            }
            sum += NumberOfChildren[n];
        }

        if (sum != N-1)
        {
            fprintf(stderr,
                "Error, the numbers of children sum to %d desecendants "
                "of the root, but array has %zu elements after the root "
                "element.\n",
                sum, N-1);
            exit(EXIT_FAILURE);
        }
    }

    /*  Compile information about the children -- set FirstChild[n] to the
        index of the element in NumberOfChildren that is for the first child
        of process n.
    */
    int FirstChild[N];
    {
        int NextChild = 1;
        for (int n = 0; n < N; ++n)
        {
            FirstChild[n] = NextChild;
            NextChild += NumberOfChildren[n];
        }
    }

    //  This is the root process.  Set p to its index.
    int p = 0;

    /*  Create children for process p.  When a child is created, it will
        return its process number, and we will loop to create children for it.
    */
    while (p >= 0)
        p = CreateChildren(NumberOfChildren, FirstChild, p);
}

示例输出:

Process 0 has pid 2648 and parent 2641.Process 1 has pid 2649 and parent 2648.Process 2 has pid 2650 and parent 2648.Process 3 has pid 2651 and parent 2649.Process 4 has pid 2652 and parent 2650.Process 5 has pid 2653 and parent 2650.Process 6 has pid 2654 and parent 2650.