Revisione completa (e relativa razionalizzazione) dei sorgenti degli esempi.

[gapil.git] / sources / SharedMem.c

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+/***************************************************************
+ *
+ * File SharedMem.c 
+ * Routine for Shared Memory use
+ *
+ * Author: S. Piccardi
+ *
+ * $Id: SharedMem.c,v 1.1 2002/12/03 11:06:05 piccardi Exp $
+ *
+ ***************************************************************/
+#include <sys/shm.h>                  /* SysV IPC shared memory declarations */
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <stdio.h>                                 /* standard I/O functions */
+#include <fcntl.h>
+#include <signal.h>                          /* signal handling declarations */
+/*
+ * Function ShmCreate:
+ * Create and attach a SysV shared memory segment to the current process.
+ *
+ * First call get a shared memory segment with KEY key access and size SIZE,
+ * by creating it with R/W privilege for the user (this is the meaning of
+ * the ored flags). The function return an identifier shmid used for any 
+ * further reference to the shared memory segment. 
+ * Second call attach the shared memory segment to this process and return a
+ * pointer to it (of void * type). 
+ * Then initialize shared memory to the given value
+ *
+ * Input:  an IPC key value
+ *         the shared memory segment size
+ * Return: the address of the segment
+ */
+void * ShmCreate(key_t ipc_key, int shm_size, char fill) 
+{
+    void * shptr;
+    int shmid;                        /* ID of the IPC shared memory segment */
+    shmid = shmget(ipc_key,shm_size,IPC_CREAT|0666);           /* get shm ID */
+    if (shmid < 0) { 
+       return (void *) shmid;
+    }
+    shptr = shmat(shmid,0,0);                      /* take the pointer to it */
+    if ( shptr == 0 ){    
+        perror("cannot attach shared memory");
+       exit(1);
+    }
+    memset((void *)shptr, fill, shm_size); /* second counter starts from "0" */
+    return shptr;
+}
+/*
+ * Function ShmFind:
+ * Find a shared memory segment 
+ * Input:  an IPC key value
+ *         the shared memory segment size
+ * Return: the address of the segment
+ */
+void * ShmFind(key_t ipc_key, int shm_size) 
+{
+    void * shptr;
+    int shmid;               /* ID of the IPC shared memory segment */
+    if ( (shmid=shmget(ipc_key,shm_size,0))<0 ){  /* find shared memory ID */
+        perror("cannot find shared memory");
+        exit(1);
+    }
+    if ( (shptr=shmat(shmid,0,0)) < 0 ){    /* take the pointer to it */
+        perror("cannot attach shared memory");
+        exit(1);
+    }
+    return shptr;
+}