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ex2.c (2135B)

      1 #include <sys/wait.h>
      2 
      3 #include <err.h>
      4 #include <stdio.h>
      5 #include <stdlib.h>
      6 #include <string.h>
      7 #include <unistd.h>
      8 
      9 /*
     10  * Εργαστήριο ΛΣ2 (Δ6) / Εργασία 1: Άσκηση 2 / 2020-2021
     11  * Ονοματεπώνυμο: Χρήστος Μαργιώλης
     12  * ΑΜ: 19390133
     13  * Τρόπος μεταγλώττισης: `cc ex2.c -o ex2`
     14  */
     15 
     16 /* 
     17  * Print a process' info. `n` indicates which process is being
     18  * printed -- for example `printproc(2)` will print P2.
     19  */
     20 static void
     21 printproc(int n)
     22 {
     23 	printf("p: %d\tpid: %d\tppid: %d\n", n, getpid(), getppid());
     24 }
     25 
     26 int
     27 main(int argc, char *argv[])
     28 {
     29 	char buf[32];	/* Message buffer */
     30 	int fd[2];	/* Pipe(2) file descriptors */
     31 	int n;		/* Bytes returned from read(2) */
     32 	int i = 3;	/* P2 will create 3 child procs */
     33 
     34 	/* Create pipe */
     35 	if (pipe(fd) < 0)
     36 		err(1, "pipe");
     37 
     38 	printproc(0);
     39 
     40 	/* Create P1 */
     41 	switch (fork()) {
     42 	case -1:
     43 		err(1, "fork");
     44 	case 0:
     45 		printproc(1);
     46 		(void)strcpy(buf, "Hello from your first child\n");
     47 		/* Close the read fd and send message to P0 */
     48 		(void)close(fd[0]);
     49 		if (write(fd[1], buf, sizeof(buf)) != sizeof(buf))
     50 			err(1, "write");
     51 		exit(EXIT_SUCCESS);
     52 	default:
     53 		/* Close the write fd and receive message from P1 */
     54 		(void)close(fd[1]);
     55 		if ((n = read(fd[0], buf, sizeof(buf))) != sizeof(buf))
     56 			err(1, "read");
     57 		/* Print the message to stdout */
     58 		if (write(STDOUT_FILENO, buf, n) != n)
     59 			err(1, "write");
     60 		if (wait(NULL) < 0)
     61 			err(1, "wait");
     62 		/* Create P2 */
     63 		switch (fork()) {
     64 		case -1:
     65 			err(1, "fork");
     66 		case 0:
     67 			printproc(2);
     68 			/* create P3, P4 and P5 */
     69 			while (i--) {
     70 				switch (fork()) {
     71 				case -1:
     72 					err(1, "fork");
     73 				case 0:
     74 					printproc(2 + i + 1);
     75 					exit(EXIT_SUCCESS);
     76 				default:
     77 					/* Wait for all children to exit first */
     78 					if (wait(NULL) < 0)
     79 						err(1, "wait");
     80 				}
     81 			}
     82 			exit(EXIT_SUCCESS);
     83 		default:
     84 			/* wait for P2 to exit */
     85 			if (wait(NULL) < 0)
     86 				err(1, "wait");
     87 		}
     88 		/* 
     89 		 * Finally, the parent process executes ps(1) after
     90 		 * everything else has exited 
     91 		 */
     92 		if (execl("/bin/ps", "ps", NULL) < 0)
     93 			err(1, "execl");
     94 	}
     95 
     96 	return 0;
     97 }