X-Git-Url: https://gapil.gnulinux.it/gitweb/?p=gapil.git;a=blobdiff_plain;f=sources%2Fmessage_getter.c;h=8b3ec2d3c0856bffc35f74b61cfe5a0975303647;hp=5ffba091b1a1c1a2b4910b026bc0194e70cb9fda;hb=9fc37da8fe691ce7ca6222773aace47c5edef3d1;hpb=5b56553e2294af812321ffaea6b296d2ad068f41

diff --git a/sources/message_getter.c b/sources/message_getter.c
index 5ffba09..8b3ec2d 100644
--- 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);
 }