changeset 17682:829919ef894a stable

lock: fixed race condition in trylock/testlock (issue3506) Suppose the following scenario: 1. Process A takes the lock (e.g. on commit). 2. Process B wants to grab the lock. Since lock file exists the exception is raised. In the catch block the testlock function is called. 3. Process A releases the lock. 4. Process B tries to read the lock file as a part of testlock function. This results in OSError (ENOENT) and since we're not inside the exception handler function this is propagated and aborts the whole operation. To fix this we now check in testlock function whether lock file actually exists and if not (i.e. if readlock fails) we just return.
author Tomasz Kleczek <tomasz.kleczek@fb.com>
date Thu, 27 Sep 2012 14:38:03 -0700
parents 07d577dae285
children 6d7db5794e8c b3f0f9a39c4e
files mercurial/lock.py
diffstat 1 files changed, 6 insertions(+), 1 deletions(-) [+]
line wrap: on
line diff
--- a/mercurial/lock.py	Sat Sep 29 13:33:55 2012 +0200
+++ b/mercurial/lock.py	Thu Sep 27 14:38:03 2012 -0700
@@ -97,7 +97,12 @@
         The lock file is only deleted when None is returned.
 
         """
-        locker = util.readlock(self.f)
+        try:
+            locker = util.readlock(self.f)
+        except OSError, why:
+            if why.errno == errno.ENOENT:
+                return None
+            raise
         try:
             host, pid = locker.split(":", 1)
         except ValueError: