Merge lp:~osomon/software-center/fixDatabaseLockError into lp:software-center

[Olivier Tilloy]

This branch fixes bug #625189 and its many duplicates.

Previously, if two instances of update-software-center-agent were running concurrently, one of them would crash when trying to acquire a write lock on the temporary DB file. With this fix, the second instance will simply exit cleanly with a warning.

Testing is relatively easy: just run two instances of update-software-center-agent simultaneously.

I’m not sure how end users would end up in this situation though: from what I understand, the only caller of update-software-center-agent is the constructor of SoftwareCenterApp, so that seems to indicate that two instance of S-C would be running simultaneously, which is not allowed…

[Michael Vogt (mvo)]

Many thanks!

review: Approve

[Michael Vogt (mvo)]

It might be that someone started s-c and exited quickly. Then started it again so (before the first update-software-center-agent would finish).

=== modified file 'utils/update-software-center-agent'
--- utils/update-software-center-agent	2011-02-08 17:24:29 +0000
+++ utils/update-software-center-agent	2011-02-22 18:04:54 +0000
@@ -72,7 +72,13 @@
         sys.exit(1)
 
     # get a writable DB
-    db = xapian.WritableDatabase(pathname, xapian.DB_CREATE_OR_OVERWRITE)
+    try:
+        db = xapian.WritableDatabase(pathname, xapian.DB_CREATE_OR_OVERWRITE)
+    except xapian.DatabaseLockError:
+        # Ref: http://launchpad.net/bugs/625189
+        logging.warn("Another instance of the update agent already holds "
+                     "a write lock on %s" % pathname)
+        sys.exit(1)
 
     # the following requires a http connection, so we do it in a 
     # seperate database