whenjobs initial version.

[whenjobs.git] / lib / flock.c

diff --git a/lib/flock.c b/lib/flock.c
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+++ b/lib/flock.c
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+/* whenjobs
+ * (C) Copyright 2012 Red Hat Inc.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
+ */
+
+#include <config.h>
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <errno.h>
+#include <sys/file.h>
+
+#include <caml/memory.h>
+#include <caml/mlvalues.h>
+#include <caml/fail.h>
+
+/* flock_exclusive_nonblocking : file_descr -> unit
+ *
+ * The reason we need this function is that OCaml only gives us access
+ * to the 'fcntl'-style of locking.  These locks are not preserved
+ * over fork(2) (WTF POSIX?) making them pretty much useless.
+ * Therefore use BSD-style flock instead.
+ */
+value
+whenjobs_flock_exclusive_nonblocking (value fdv)
+{
+  CAMLparam1 (fdv);
+
+  /* file_descr is opaque, but on un*x-like platforms it's an integer */
+  int fd = Int_val (fdv);
+
+  if (flock (fd, LOCK_EX|LOCK_NB) == -1)
+    caml_failwith (strerror (errno));
+
+  CAMLreturn (Val_unit);
+}