From 08860d002a81ca71406c49c33e300441bc110d50 Mon Sep 17 00:00:00 2001
From: Santo Cariotti <santo@dcariotti.me>
Date: Fri, 24 Sep 2021 20:09:56 +0200
Subject: os: add homework 8
---
Year_2/OS/hw/hw8.c | 163 +++++++++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 163 insertions(+)
create mode 100644 Year_2/OS/hw/hw8.c
diff --git a/Year_2/OS/hw/hw8.c b/Year_2/OS/hw/hw8.c
new file mode 100644
index 0000000..0e2ecc4
--- /dev/null
+++ b/Year_2/OS/hw/hw8.c
@@ -0,0 +1,163 @@
+/*
+ Homework n.8
+
+ Modificare l'homework precedente (n.7) sostituendo il canale di comuniciazione
+ offerto dalla coda di messaggi tra padre e figlio con un segmento di memoria
+ condiviso e una coppia di semafori (esattamente due) opportunamente utilizzati
+ per il coordinamento.
+
+*/
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/ipc.h>
+#include <sys/sem.h>
+#include <sys/shm.h>
+#include <sys/types.h>
+#include <sys/wait.h>
+#include <unistd.h>
+
+#define DIM_MSG 1024
+
+int
+WAIT(int des, int n)
+{
+ struct sembuf op[1] = { { n, -1, 0 } };
+ return semop(des, op, 1);
+}
+
+int
+SIGNAL(int des, int n)
+{
+ struct sembuf op[1] = { { n, 1, 0 } };
+ return semop(des, op, 1);
+}
+
+void
+execute(int id_shm, int id_sem)
+{
+ pid_t pid;
+ char* msg;
+ char command[DIM_MSG];
+ int n;
+ char* p;
+ int pipefd[2];
+
+ if ((msg = (char*)shmat(id_shm, NULL, 0)) == (char*)-1) {
+ perror("shmat");
+ exit(1);
+ }
+
+ while (1) {
+ WAIT(id_sem, 0);
+
+ /* The variable `command` will be the substring of the passed string
+ * until the first space, ignoring all parameters */
+ n = 0;
+ p = msg;
+ while (*p != '\0') {
+ if (*p == ' ')
+ break;
+ n++;
+ p++;
+ }
+
+ strncpy(command, msg, n);
+ command[n] = '\0';
+
+ if (strcmp(command, "exit") == 0)
+ break;
+
+ if (pipe(pipefd) == -1) {
+ perror("pipe");
+ exit(1);
+ }
+
+ pid = fork();
+ if (pid == -1) {
+ perror("fork");
+ exit(1);
+ }
+
+ if (pid == 0) {
+ dup2(pipefd[1], 1);
+ dup2(pipefd[1], 2);
+ close(pipefd[0]);
+ execlp(command, "", NULL);
+ fprintf(stderr, "Error executing '%s'\n", command);
+ exit(1);
+ } else {
+ wait(NULL);
+
+ close(pipefd[1]);
+ n = read(pipefd[0], msg, 1024);
+ msg[n] = '\0';
+ SIGNAL(id_sem, 1);
+ close(pipefd[0]);
+ }
+ }
+}
+
+int
+main()
+{
+ int id_shm, id_sem;
+ int pid;
+ int n;
+ char* msg;
+
+ if ((id_shm = shmget(IPC_PRIVATE, DIM_MSG, IPC_CREAT | 0644)) == -1) {
+ perror("shmget");
+ exit(1);
+ }
+
+ if ((id_sem = semget(IPC_PRIVATE, 2, IPC_CREAT | 0644)) == -1) {
+ perror("semget");
+ exit(1);
+ }
+
+ /* Set values to 0 */
+ semctl(id_sem, 0, SETVAL, 0);
+ semctl(id_sem, 1, SETVAL, 0);
+
+ pid = fork();
+ if (pid == -1) {
+ perror("fork");
+ exit(1);
+ }
+
+ if ((msg = (char*)shmat(id_shm, NULL, 0)) == (char*)-1) {
+ perror("shmat");
+ exit(1);
+ }
+
+ if (pid != 0) {
+ while (1) {
+ printf("Insert a command: ");
+ fgets(msg, DIM_MSG, stdin);
+ n = strlen(msg);
+ msg[n - 1] = '\0';
+
+ /* Ignore empty string */
+ if (strcmp(msg, "") == 0)
+ continue;
+
+ SIGNAL(id_sem, 0);
+
+ if (strcmp(msg, "exit") == 0) {
+ break;
+ }
+
+ WAIT(id_sem, 1);
+ printf("%s\n", msg);
+ sleep(1);
+ }
+ } else {
+ execute(id_shm, id_sem);
+ }
+
+ shmctl(id_shm, IPC_RMID, NULL);
+ semctl(id_sem, 0, IPC_RMID, 0);
+
+ return 0;
+}
--
cgit v1.2.3-18-g5258