Risistemati ed insiriti nella relativa sezione gli esempi di uso dei

[gapil.git] / sources / message_getter.c

diff --git a/sources/message_getter.c b/sources/message_getter.c
index 5ffba091b1a1c1a2b4910b026bc0194e70cb9fda..8b3ec2d3c0856bffc35f74b61cfe5a0975303647 100644 (file)
--- a/sources/message_getter.c
+++ b/sources/message_getter.c
@@ -93,42 +93,38 @@ int main(int argc, char *argv[])
         usage();
     }
     Signal(SIGINT, HandSigInt);
-    // Get shared memory segment
-    shm_ptr = CreateShm(shmname, MSGMAXSIZE, 0666, 0);
-    if ( shm_ptr == NULL) {
+    // get a shared memory segment
+    if ((shm_ptr = CreateShm(shmname, MSGMAXSIZE, 0666, 0)) == NULL) {
        perror("Cannot find shared memory");
        exit(1);
     }
-    // set initial string
-    strncpy((char *) shm_ptr, argv[optind], MSGMAXSIZE);
-    // open the semaphore or create it locked
-    if ( (sem = sem_open(semname, O_CREAT, 0666, 0)) == SEM_FAILED ) {
+    // get a locked semaphore
+    if ((sem = sem_open(semname, O_CREAT|O_EXCL, 0666, 0)) == SEM_FAILED) {
        perror("Cannot open semaphore");
        exit(1);
     }
-    // check if first time creation, and unlock
-    if ( sem_getvalue(sem, &i) != 0) {
-       perror("cannot get initial semaphore value");
+    // set initial string
+    strncpy((char *) shm_ptr, argv[optind], MSGMAXSIZE);
+    // do initial release
+    if (sem_post(sem) != 0) {
+       perror("cannot do semaphore initial release");
        exit(1);
-    } else 
-       if (i == 0)
-           if ( sem_post(sem) != 0) {
-               perror("cannot do semaphore initial release");
-               exit(1);
-           }
+    }
     // main loop
     while(1) {
-       // acquire semaphore
-       if ( sem_wait(sem) != 0) {
+       if (sem_getvalue(sem, &i) !=0) {             // get sem values
+           perror("cannot get semaphore value");
+           exit(1);
+       }
+       printf("sem=%i, ", i);                       // print sem values
+       t = time(NULL);                              // get time
+       printf("%s", ctime(&t));                     // print time
+       if (sem_wait(sem) != 0) {                    // acquire semaphore
            perror("cannot use semaphore");
            exit(1);
        }
-       t = time(NULL);
-       printf("%s", ctime(&t));
-       sem_getvalue(sem, &i);
-       printf("sem=%i,  ", i);
-       printf("message: %s\n", (char *) shm_ptr );
-       if ( sem_post(sem) != 0) {
+       printf("message: %s\n", (char *) shm_ptr );  // print message
+       if (sem_post(sem) != 0) {                    // release semaphore
            perror("cannot release semaphore");
            exit(1);
        }
@@ -152,7 +148,7 @@ void usage(void) {
 
 void HandSigInt(int sig)
 {
-    RemoveShm(shmname);
-    sem_unlink(semname);
+    if (RemoveShm(shmname) != 0) perror("Cannot remove shared memory");
+    if (sem_unlink(semname)!= 0) perror("Cannot remove semaphore") ;
     exit(0);
 }