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POBi-directional inter-process communication using two pipes
 

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    <p>I am trying to write code that forks a subprocess and communicates with it using pipes. I am using two pipes - one for writing to, and the other for reading from the standard streams of the subprocess. Here's what I have so far:</p> <pre><code>#include &lt;stdio.h&gt; #include &lt;stdlib.h&gt; #include &lt;unistd.h&gt; #include &lt;signal.h&gt; #include &lt;string.h&gt; void read_move(int fd) { FILE *stream = fdopen(fd, "r"); char c; setvbuf(stream, NULL, _IONBF, BUFSIZ); while ((c = fgetc(stream)) != EOF) { putchar(c); } fclose(stream); } void write_move(int fd, const char *move) { FILE *stream = fdopen(fd, "w"); setvbuf(stream, NULL, _IONBF, BUFSIZ); fprintf(stream, "%s", move); fclose(stream); } int main() { pid_t pid; int wpipe[2]; int rpipe[2]; if (pipe(wpipe) || pipe(rpipe)) { fprintf(stderr, "Pipe creation failed.\n"); return EXIT_FAILURE; } pid = fork(); if (pid == 0) { /* gnuchess process */ setvbuf(stdin, NULL, _IONBF, BUFSIZ); setvbuf(stdout, NULL, _IONBF, BUFSIZ); setvbuf(stderr, NULL, _IONBF, BUFSIZ); dup2(wpipe[0], STDIN_FILENO); dup2(rpipe[1], STDOUT_FILENO); dup2(rpipe[1], STDERR_FILENO); close(wpipe[0]); close(wpipe[1]); close(rpipe[0]); close(rpipe[1]); if (execl("/usr/games/gnuchess", "gnuchess", "-x", NULL) == -1) { fprintf(stderr, "Exec failed.\n"); return EXIT_FAILURE; } return EXIT_SUCCESS; } /* parent process */ printf("Sending move to GNU Chess... \n"); close(wpipe[0]); /* Close other end */ write_move(wpipe[1], "c3\n"); printf("Reading response... \n"); close(rpipe[1]); /* Close other end */ read_move(rpipe[0]); /* clean up */ close(wpipe[1]); close(rpipe[0]); /* kill gnuchess */ kill(pid, SIGTERM); return EXIT_SUCCESS; } </code></pre> <p>The output of the above program is</p> <pre><code>Sending move to GNU Chess... Reading response... </code></pre> <p>It gets stuck at the <code>getline</code> call in the <code>read_move</code> function, waiting for input. But I don't understand how that's possible, since I have closed the other end.</p> <p>What am I doing wrong?</p> <p>EDIT: I changed the <code>read_move</code> method and closed the pipe ends in the child process after the <code>dup2</code> calls.</p>
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