diff tests/lockdelay.py @ 28289:d493d64757eb stable 3.7.2

hg: obtain lock when creating share from pooled repo (issue5104)

There are race conditions between clients performing a shared clone
to pooled storage:

1) Clients race to create the new shared repo in the pool directory
2) 1 client is seeding the repo in the pool directory and another goes
   to share it before it is fully cloned

We prevent these race conditions by obtaining a lock in the pool
directory that is derived from the name of the repo we will be
accessing.

To test this, a simple generic "lockdelay" extension has been added.
The extension inserts an optional, configurable delay before or after
lock acquisition. In the test, we delay 2 seconds after lock acquisition
in the first process and 1 second before lock acquisition in the 2nd
process. This means the first process has 1s to obtain the lock. There
is a race condition here. If we encounter it in the wild, we could
change the dummy extension to wait on the lock file to appear instead
of relying on timing. But that's more complicated. Let's see what
happens first.

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/tests/lockdelay.py	Sat Feb 27 18:22:49 2016 -0800
@@ -0,0 +1,26 @@
+# Dummy extension that adds a delay after acquiring a lock.
+#
+# This extension can be used to test race conditions between lock acquisition.
+
+from __future__ import absolute_import
+
+import os
+import time
+
+from mercurial import (
+    lock as lockmod,
+)
+
+class delaylock(lockmod.lock):
+    def lock(self):
+        delay = float(os.environ.get('HGPRELOCKDELAY', '0.0'))
+        if delay:
+            time.sleep(delay)
+        res = super(delaylock, self).lock()
+        delay = float(os.environ.get('HGPOSTLOCKDELAY', '0.0'))
+        if delay:
+            time.sleep(delay)
+        return res
+
+def extsetup(ui):
+    lockmod.lock = delaylock