--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/osdep/unix/flockcyg.c	Mon Sep 14 15:17:45 2009 +0900
@@ -0,0 +1,92 @@
+/* ========================================================================
+ * Copyright 1988-2006 University of Washington
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * 
+ * ========================================================================
+ */
+
+/*
+ * Program:	flock emulation via fcntl() locking
+ *
+ * Author:	Mark Crispin
+ *		Networks and Distributed Computing
+ *		Computing & Communications
+ *		University of Washington
+ *		Administration Building, AG-44
+ *		Seattle, WA  98195
+ *		Internet: MRC@CAC.Washington.EDU
+ *
+ * Date:	10 April 2001
+ * Last Edited:	30 August 2006
+ */
+
+
+/* Cygwin does not seem to have the design flaw in fcntl() locking that
+ * most other systems do (see flocksim.c for details).  If some cretin
+ * decides to implement that design flaw, then Cygwin will have to use
+ * flocksim.  Also, we don't test NFS either.
+ *
+ * However, Cygwin does have the Windows misfeature (introduced in NT 4.0)
+ * that you can not write to any segment which has a shared lock, and you
+ * can't lock a zero-byte segment either.  This screws up the shared-write
+ * mailbox drivers (mbx, mtx, mx, and tenex).  As a workaround, we'll only
+ * lock the first byte of the file, meaning that you can't write that byte
+ * shared.  It's been suggested to lock the maximum off_t type, but that
+ * risks having a future version of Windows (or Cygwin) deciding that this
+ * also means "no lock".
+ */
+
+#undef flock			/* name is used as a struct for fcntl */
+
+/* Emulator for flock() call
+ * Accepts: file descriptor
+ *	    operation bitmask
+ * Returns: 0 if successful, -1 if failure under BSD conditions
+ */
+
+int flocksim (int fd,int op)
+{
+  char tmp[MAILTMPLEN];
+  int logged = 0;
+  struct flock fl;
+				/* lock one bytes at byte 0 */
+  fl.l_whence = SEEK_SET; fl.l_start = 0; fl.l_len = 1;
+  fl.l_pid = getpid ();		/* shouldn't be necessary */
+  switch (op & ~LOCK_NB) {	/* translate to fcntl() operation */
+  case LOCK_EX:			/* exclusive */
+    fl.l_type = F_WRLCK;
+    break;
+  case LOCK_SH:			/* shared */
+    fl.l_type = F_RDLCK;
+    break;
+  case LOCK_UN:			/* unlock */
+    fl.l_type = F_UNLCK;
+    break;
+  default:			/* default */
+    errno = EINVAL;
+    return -1;
+  }
+  while (fcntl (fd,(op & LOCK_NB) ? F_SETLK : F_SETLKW,&fl))
+    if (errno != EINTR) {
+      /* Can't use switch here because these error codes may resolve to the
+       * same value on some systems.
+       */
+      if ((errno != EWOULDBLOCK) && (errno != EAGAIN) && (errno != EACCES)) {
+	sprintf (tmp,"Unexpected file locking failure: %s",strerror (errno));
+				/* give the user a warning of what happened */
+	MM_NOTIFY (NIL,tmp,WARN);
+	if (!logged++) syslog (LOG_ERR,"%s",tmp);
+	if (op & LOCK_NB) return -1;
+	sleep (5);		/* slow things down for loops */
+      }
+				/* return failure for non-blocking lock */
+      else if (op & LOCK_NB) return -1;
+    }
+  return 0;			/* success */
+}