new file mode 100644
--- /dev/null
+++ b/mercurial/lock.py
@@ -0,0 +1,46 @@
+# lock.py - simple locking scheme for mercurial
+#
+# Copyright 2005 Matt Mackall <mpm@selenic.com>
+#
+# This software may be used and distributed according to the terms
+# of the GNU General Public License, incorporated herein by reference.
+
+import os, time
+
+class LockHeld(Exception):
+ pass
+
+class lock:
+ def __init__(self, file, wait = 1):
+ self.f = file
+ self.held = 0
+ self.wait = wait
+ self.lock()
+
+ def __del__(self):
+ self.release()
+
+ def lock(self):
+ while 1:
+ try:
+ self.trylock()
+ return 1
+ except LockHeld, inst:
+ if self.wait:
+ time.sleep(1)
+ continue
+ raise inst
+
+ def trylock(self):
+ pid = os.getpid()
+ try:
+ os.symlink(str(pid), self.f)
+ self.held = 1
+ except:
+ raise LockHeld(os.readlink(self.f))
+
+ def release(self):
+ if self.held:
+ self.held = 0
+ os.unlink(self.f)
+