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

[gapil.git] / sources / Mutex.c

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+/*****************************************************************************
+ *
+ * File Mutex.c: define a set of functions for mutex manipulation 
+ *
+ * Author: S. Piccardi Dec. 2002
+ *
+ * $Id: Mutex.c,v 1.1 2002/12/03 11:06:05 piccardi Exp $
+ *
+ *****************************************************************************/
+#include <sys/sem.h>     /* IPC semaphore declarations */
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+#include <signal.h>      /* signal handling declarations */
+
+#include "Gapil.h"
+/*
+ * Function MutexCreate: create a mutex/semaphore
+ *
+ * First call create a semaphore, using the given key. 
+ * We want only one semaphore so we set second argument to 1; third 
+ * parameter is the flag argument, and is set to create a semaphore 
+ * with R/W privilege for the user.
+ * Second call initialize the semaphore to 1 (unlocked)
+ *
+ * Input: an IPC key value (to create an unique semaphore)
+ * Return: the semaphore id# or -1 on error
+ */
+int MutexCreate(key_t ipc_key) 
+{
+    const union semun semunion={1};             /* semaphore union structure */
+    int sem_id, ret;
+    sem_id = semget(ipc_key, 1, IPC_CREAT|0666);         /* get semaphore ID */
+    if (sem_id == -1) {                              /* if error return code */
+       return sem_id;
+    }
+    ret = semctl(sem_id, 0, SETVAL, semunion);             /* init semaphore */
+    if (ret == -1) {
+       return ret;
+    }
+    return sem_id;
+}
+/*
+ * Function MutexFind: get the semaphore/mutex Id given the IPC key value
+ *
+ * Input: an IPC key value
+ */
+int MutexFind(key_t ipc_key) 
+{
+    return semget(ipc_key,1,0);
+}
+/*
+ * Function MutexRead: read the current value of the mutex/semaphore
+ *
+ * Input:  a semaphore id #
+ * Return: the semaphore value
+ */
+int MutexRead(int sem_id) 
+{
+    return semctl(sem_id, 0, GETVAL);
+}
+/*
+ * Define sembuf structures to lock and unlock the semaphore 
+ * (used to implement a mutex)
+ */
+struct sembuf sem_lock={                                /* to lock semaphore */
+    0,                                   /* semaphore number (only one so 0) */
+    -1,                                    /* operation (-1 to use resource) */
+    SEM_UNDO};                                /* flag (set for undo at exit) */
+struct sembuf sem_ulock={                             /* to unlock semaphore */
+    0,                                   /* semaphore number (only one so 0) */
+    1,                                  /* operation (1 to release resource) */
+    SEM_UNDO};                                      /* flag (in this case 0) */
+/*
+ * Function MutexLock: to lock a mutex/semaphore
+ *
+ * Input:  a semaphore id #
+ * Output: semop return code  (0 OK, -1 KO)
+ */
+int MutexLock(int sem_id) 
+{
+    return semop(sem_id, &sem_lock, 1);
+}
+/*
+ * Function MutexUnlock: to unlock a mutex/semaphore
+ *
+ * Input:  a semaphore id #
+ * Return: semop return code (0 OK, -1 KO)
+ */
+int MutexUnlock(int sem_id) 
+{
+    return semop(sem_id, &sem_ulock, 1);
+}