first commit

src/SharedMemoryAccess.cpp

@@ -0,0 +1,65 @@
+//
+// Created by Cigerxwin  Chaker on 05.11.19.
+//
+#include <iostream>
+#include <sys/_types.h>
+#include <sys/ipc.h>
+#include <sys/shm.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <sys/stat.h>
+//#include "sharedMemory.h"  /* header is important for the shmID. name could be different. maybe not needed cause: (shmget(memory_access_key, NULL, 0)) */
+#include <sys/sem.h>
+#include <unistd.h>
+
+int initSemaphore (void) {
+    /* Testen, ob das Semaphor bereits existiert */
+    semId = semget (semKey, 0, IPC_PRIVATE);
+    if (semId < 0) {
+        /* ... existiert noch nicht, also anlegen        */
+        /* Alle Zugriffsrechte der Dateikreierungsmaske */
+        /* erlauben                                     */
+        umask(0);
+        semId = semget (semKey, 1, IPC_CREAT | IPC_EXCL | PERM);
+        if (semId < 0) {
+            return -1;
+        }
+        /* Semaphor mit 1 initialisieren */
+        if (semctl (semId, 0, SETVAL, (int) 1) == -1)
+            return -1;
+    }
+    return 1;
+}
+
+int semaphoreOperation (int op) {
+    semaphore.sem_op = op;
+    semaphore.sem_flg = SEM_UNDO;
+    if( semop (semId, &semaphore, 1) == -1) {
+        perror(" semop ");
+        exit (EXIT_FAILURE);
+    }
+    return 1;
+}
+
+void writeToShm(char* text, int size) {
+    int shmId = shmget(memoryAccessKey, NULL, 0);
+    if(shmId < 0 ) {
+        exit(EXIT_FAILURE);
+        /* we could return -1, not sure if it will be useful to continue after there is no shm allocated for any reason*/
+    } else {
+        char *shm_pointer = (char *) shmat(shmId, NULL, 0);
+        semaphore_operation(LOCK);
+        memcpy(shm_pointer, text, size);
+        semaphore_operation(UNLOCK);
+    }
+}
+
+char* getShmPointer() {
+    int shmId = shmget(memoryAccessKey, NULL, 0);
+    if(shmId < 0) {
+        exit(EXIT_FAILURE);
+        /* we could return -1, not sure if it will be useful to continue after there is no shm allocated for any reason*/
+    } else {
+        return (char *) shmat(shmId, NULL, 0);
+    }
+}

src/SharedMemoryAccess.h

@@ -0,0 +1,20 @@
+//
+// Created by Cigerxwin  Chaker on 05.11.19.
+//
+
+#ifndef LIBRARY_SHAREDMEMORYACCESSS_H
+#define LIBRARY_SHAREDMEMORYACCESSS_H
+
+#define PERM 0666      /* Zugriffsrechte */
+#define LOCK       -1
+#define UNLOCK      1
+#define SemKey  123458L
+
+int memoryAccessKey; /* var type is int. but could be another type. */ //TODO: look after type in sharedmemory group
+int semId;
+struct sembuf semaphore;
+int initSemaphore (void);
+int semaphoreOperation (int op);
+char* getShmPointer(void);
+void writeToShm(char* text, int size);
+#endif //LIBRARY_SHAREDMEMORYACCESSS_H