Semaphoren

Semaphoren/semaphoren.c

+/* gcc sema_vorgabe.c -o sema_vorgabe -lpthread */
+#include <unistd.h>
+#include <stdlib.h>
+#include <stdio.h>
+#include <pthread.h>
+#include <semaphore.h>
+
+sem_t sem_1; 
+sem_t sem_2;
+
+void *print_stern (void *dummy) {
+   char ch = '*';
+
+   while(1) {
+      sem_wait(&sem_1);
+      putchar(ch);
+      fflush(stdout);
+      sem_post(&sem_2);
+  }
+
+  return NULL;
+}
+
+void *print_minus (void *dummy) {
+   char ch = '-';
+
+   while(1) {
+      sem_wait(&sem_2);
+      putchar(ch);
+      fflush(stdout);
+      sem_post(&sem_1);
+   }
+
+  return NULL;
+}
+
+int main () {
+   pthread_t tref1, tref2;
+ 
+   if(sem_init(&sem_1, 0, 0)){
+	perror("sem_1 init fail");
+	return -1;
+   }
+   if(sem_init(&sem_2, 0, 1)){
+	perror("sem_2 init fail");
+   	return -1;
+   }
+  
+   if (pthread_create (&tref1, NULL, print_minus, NULL)) {
+      fprintf(stderr, "error: creating thread 1 failed.\n");
+      return EXIT_FAILURE;
+   }
+ 
+   if (pthread_create (&tref2, NULL, print_stern, NULL)) {
+      fprintf(stderr, "error: creating thread 2 failed.\n");
+      return EXIT_FAILURE;
+   }
+
+   if (pthread_join (tref1, NULL)) {
+      fprintf(stderr, "error: joining thread 1 failed.\n");
+      return EXIT_FAILURE;
+   }
+   if (pthread_join (tref2, NULL)) {
+      fprintf(stderr, "error: joining thread 2 failed.\n");
+      return EXIT_FAILURE;
+   }
+
+   return EXIT_SUCCESS;
+}