C语言中父母与两个孩子之间的管道

修改与开放流关联的文件描述符是不好的消息。我认为这很可能会给您带来麻烦，此外，这里不需要这样做。父级应该改用fdopen()在管道末端上打开新流，并通过子级而不是通过标准流对其子级进行I / O。除了更安全之外，还使流程的原始标准流可用于与其父流程进行通信。

使用这种方法，您甚至可以流传输要在进程之间来回排序的字符串，而不是在每个进程的内存中冗余地缓冲它们的块。例如，您可以执行以下操作：

#define _GNU_SOURCE
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <unistd.h>

int main(int argc, char * argv[]) {
    char * buffer = NULL;
    size_t buflen = 0;
    int nrrows;
    int fdpc1[2];
    int fdcp1[2];
    int fdpc2[2];
    int fdcp2[2];
    pid_t chpid1;
    pid_t chpid2;
    FILE *pipeout;
    FILE *pipein1;
    FILE *pipein2;
    int half;
    int i;

    fprintf(stderr, "%s!!!!!!!!!!!!!!!!!\n", argv[0]);

    getline(&buffer, &buflen, stdin);
    fprintf(stderr, "number: %s from %s\n", buffer, argv[0]);
    nrrows = strtol(buffer, NULL, 10);

    if(nrrows <= 0) {
        fprintf(stderr, "This is not a valid >0 number\n");
        return EXIT_FAILURE;
    } else if (nrrows == 1) {
        /* ... read and echo back the one row ... */
        getline(&buffer, &buflen, stdin);
        fprintf(stderr, "%s", buffer);
        return EXIT_SUCCESS;
    }

    /* There are at least two rows to sort */

    if (pipe(fdcp1) < 0) {
        fprintf(stderr, "pipe unsuccessfull\n");
        return EXIT_FAILURE;
    }
    if (pipe(fdpc1) < 0) {
        fprintf(stderr, "pipe unsuccessfull\n");
        return EXIT_FAILURE;
    }

    chpid1 = fork();
    if (chpid1 == 0) {
        /* this is child process 1 */
        close(fdcp1[1]);
        close(fdpc1[0]);
        dup2(fdcp1[0], STDIN_FILENO);
        close(fdcp1[0]);
        dup2(fdpc1[1], STDOUT_FILENO);
        close(fdpc1[1]);
        execlp("./forksort", "child1", NULL);
    } else if (chpid1 < 0) {
        fprintf(stderr, "fork unsuccessfull\n");
        return EXIT_FAILURE;
    }

    /* this is the parent process */

    close(fdcp1[0]);
    close(fdpc1[1]);

    if (pipe(fdcp2) < 0) {
        fprintf(stderr, "pipe unsuccessfull\n");
        return EXIT_FAILURE;
    }
    if (pipe(fdpc2) < 0) {
        fprintf(stderr, "pipe unsuccessfull\n");
        return EXIT_FAILURE;
    }

    chpid2 = fork();
    if (chpid2 == 0) {
        /* this is child process 2 */
        close(fdcp1[1]);
        close(fdpc1[0]);
        close(fdcp2[1]);
        close(fdpc2[0]);
        dup2(fdcp2[0], STDIN_FILENO);
        close(fdcp2[0]);
        dup2(fdpc2[1], STDOUT_FILENO);
        close(fdpc2[1]);
        execlp("./forksort", "child2", NULL);
    } else if (chpid2 < 0) {
        fprintf(stderr, "fork unsuccessfull\n");
        return EXIT_FAILURE;
    }

    /* this is the parent process */

    close(fdcp2[0]);
    close(fdpc2[1]);

    /* copy the first half of the lines from input to child 1 */

    pipeout = fdopen(fdcp1[1], "w");
    if (pipeout == NULL) {
        fprintf(stderr, "fdopen unsuccessful\n");
        return EXIT_FAILURE;
    }

    half = nrrows / 2;
    fprintf(pipeout, "%d\n", half);
    for (i = 0; i < half; i += 1) {
        getline(&buffer, &buflen, stdin);
        fprintf(stderr,"row[%d] from %s: %s", i, argv[0], buffer);
        fputs(buffer, pipeout);
    }
    fclose(pipeout);

    /* copy the second half of the lines from input to child 2 */

    pipeout = fdopen(fdcp2[1], "w");
    if (pipeout == NULL) {
        fprintf(stderr, "fdopen unsuccessful\n");
        return EXIT_FAILURE;
    }

    fprintf(pipeout, "%d\n", nrrows - half);
    for (; i < nrrows; i += 1) {
        getline(&buffer, &buflen, stdin);
        fprintf(stderr,"row[%d] from %s: %s", i, argv[0], buffer);
        fputs(buffer, pipeout);
    }
    fclose(pipeout);

    /* now read and merge sorted lines from the children */

    pipein1 = fdopen(fdpc1[0], "r");
    pipein2 = fdopen(fdpc2[0], "r");
    if (pipein1 == NULL || pipein2 == NULL) {
        fprintf(stderr, "fdopen unsuccessful\n");
        return EXIT_FAILURE;
    }

    /* ... */

    fclose(pipein1);
    fclose(pipein2);

    return 0;
}