* ability to use locks on database file

src/database.c

@@ -81,6 +81,14 @@ simdb_open(const char *path, int mode, int *error) {
     return NULL;
   }
 
+  if ((mode & SIMDB_FLAG_WRITE) && (mode & (SIMDB_FLAG_LOCK|SIMDB_FLAG_LOCKNB))) {
+    int locktype = (mode & SIMDB_FLAG_LOCKNB) ? F_TLOCK : F_LOCK;
+    if (lockf(fd, locktype, 0) < 0) {
+      *error = SIMDB_ERR_LOCK;
+      return NULL;
+    }
+  }
+
   errno = 0;
   bytes = pread(fd, buf, SIMDB_REC_LEN, 0);
   if (bytes < SIMDB_REC_LEN) {
@@ -106,8 +114,7 @@ simdb_open(const char *path, int mode, int *error) {
     return NULL;
   }
 
-  if (mode & SIMDB_FLAG_WRITE)
-    flags |= SIMDB_FLAG_WRITE;
+  flags = mode & SIMDB_FLAGS_MASK;
 
   /* all seems to be ok */
 
@@ -166,6 +173,8 @@ simdb_error(int error) {
     return "wrong parameters passed to finction";
   } else if (error == SIMDB_ERR_SAMPLER) {
     return "given file not an image, damaged or has unsupported format";
+  } else if (error == SIMDB_ERR_LOCK) {
+    return "can't add lock on database file";
   }
   return "unknown error";
 }

src/simdb.h

@@ -12,7 +12,10 @@
 /**
  * @defgroup SIMDBFlags Database runtime flags
  *  @{ */
+#define SIMDB_FLAGS_MASK    0xFF
 #define SIMDB_FLAG_WRITE    1 << (0 + 0)  /**< database has write access */
+#define SIMDB_FLAG_LOCK     1 << (0 + 1)  /**< use locks for file with write access (only with @ref SIMDB_FLAG_WRITE) */
+#define SIMDB_FLAG_LOCKNB   1 << (0 + 2)  /**< same as above, but not wait for lock (only with @ref SIMDB_FLAG_WRITE) */
 /** @} */
 
 /**
@@ -43,6 +46,7 @@
 #define SIMDB_ERR_READONLY    -6 /**< database opened in read-only mode */
 #define SIMDB_ERR_USAGE       -7 /**< wrong arguments passed */
 #define SIMDB_ERR_SAMPLER     -8 /**< given file not an image, damaged or has unsupported format */
+#define SIMDB_ERR_LOCK        -9 /**< can't add lock on database file */
 /** @} */
 
 /** opaque database handler */