Shared memory, esempio di LockFile, di Mutex con il file locking,

[gapil.git] / sources / Mutex.c

diff --git a/sources/Mutex.c b/sources/Mutex.c
index ddbb9b11354447b120502d9f6924db08a8c5e2fc..d0099982305d5d42c0b1c36ac3baead2afac66f1 100644 (file)
--- a/sources/Mutex.c
+++ b/sources/Mutex.c
@@ -22,7 +22,7 @@
  *
  * Author: S. Piccardi Dec. 2002
  *
- * $Id: Mutex.c,v 1.2 2002/12/03 22:30:11 piccardi Exp $
+ * $Id: Mutex.c,v 1.3 2002/12/05 23:38:22 piccardi Exp $
  *
  *****************************************************************************/
 #include <sys/sem.h>     /* IPC semaphore declarations */
@@ -109,3 +109,63 @@ int MutexUnlock(int sem_id)
 {
     return semop(sem_id, &sem_ulock, 1);
 }
+/***************************************************************************** 
+ *
+ * File locking mutex 
+ *
+ * Create a mutex usinf file locking. Use file locking to lock a file
+ * as a mutex request, and unlock it as a mutex release.
+ *
+ * Author: S. Piccardi Dec. 2002
+ *
+ *****************************************************************************/
+/*
+ * Function LockMutex: lock a file (creating it if not existent).  
+ *
+ * Input:  a filename
+ * Output: a return code  (0 OK, -1 KO)
+ */
+int LockMutex(const char *path_name)
+{
+    int fd, res;
+    struct flock lock;                                /* file lock structure */
+    /* first open the file (creating it if not existent) */
+    if ( (fd = open(path_name, O_EXCL|O_CREAT)) < 0) {    /* first open file */
+       return fd;
+    }
+    /* set flock structure */
+    lock.l_type = F_WRLCK;                        /* set type: read or write */
+    lock.l_whence = SEEK_SET;        /* start from the beginning of the file */
+    lock.l_start = 0;                  /* set the start of the locked region */
+    lock.l_len = 0;                   /* set the length of the locked region */
+    /* do locking */
+    if ( (res = fcntl(fd, F_SETLKW, &lock)) < 0 ) {
+       return res;
+    }
+    return 0;
+}
+/*
+ * Function UnlockMutex: unlock a file.  
+ *
+ * Input:  a filename
+ * Output: a return code  (0 OK, -1 KO)
+ */
+int UnlockMutex(const char *path_name)
+{
+    int fd, res;
+    struct flock lock;                                /* file lock structure */
+    /* first open the file */
+    if ( (fd = open(path_name, O_RDWR)) < 0) {            /* first open file */
+       return fd;
+    }
+    /* set flock structure */
+    lock.l_type = F_UNLCK;                               /* set type: unlock */
+    lock.l_whence = SEEK_SET;        /* start from the beginning of the file */
+    lock.l_start = 0;                  /* set the start of the locked region */
+    lock.l_len = 0;                   /* set the length of the locked region */
+    /* do locking */
+    if ( (res = fcntl(fd, F_SETLK, &lock)) < 0 ) {
+       return res;
+    }
+    return 0;
+}