How Crashplan breaks xpcshell tests on Windows

I recently switched to a Windows laptop and have been going through the usual teething pains related. One thing that confused me though was that when I was running xpcshell tests on my new machine they would frequently fail with access denied errors. I’ve seen this sort of thing before so I know some service was monitoring files and opening them after they had changed, when this happens they can’t be deleted or edited until the service closes them again and often tests open, close and delete files so fast that there isn’t time for that to happen.

It took me a little while to remember that I can just use Process Monitor to track down the offending service. Just fire it up, set a filter to only include results to a particular directory (the temp directory in this case) and go create a file there and see what shows up. I was quite surprised to see Crashplan, the backup software I (and probably many people in Mozilla) use. Surprised because Crashplan isn’t set to backup my temp directory and really I shudder to think what the performance cost is of something continually accessing every file that changes in the temp directory.

Turns out you can turn it off though. Hidden in the depths of Crashplan’s advanced backup settings is an option to disable real-time filesystem watching. From what I can see online the downside to this is that files will only be backed up once a day, but that’s a pretty fine tradeoff to¬† having functioning xpcshell tests for me. There is also an option to put crashplan to sleep for an hour or so, that seems to work too but I don’t know exactly what that does.

It confuses me a little why Crashplan monitors files it never intends to backup (even when the backup server isn’t connected and backups aren’t in progress) and it is quite a lot of file accesses it does too. Seems likely to be a bug to me but at least I can workaround it for now.

WebApp Tabs, version control and GitHub

The extension I’ve been working on in my spare time for the past couple of weeks is now available as a first (hopefully not too buggy) release. It lets you open WebApps in Thunderbird, properly handling loading new links into Firefox and making all features like spellchecking work in Thunderbird (most other extensions I found didn’t do this). You can read more about the actual extension at its homepage.

Mostly I’ve been really encouraged during the development of this at just how far our platform has come for developing restartless add-ons. When we first made it possible in Firefox 4 there was a whole list of things that were quite difficult to do but we’ve come a long way since then. While there are still things that are difficult there are lots of things that are now pretty straightforward. My add-on loads simple XUL overlays, style overlays, installs JS XPCOM components with category manager registration, all similar to older add-ons. In fact I’m struggling to think of things that it is still hard to do though I’m sure other more prolific developers will have plenty of comments on that!

The other thing I’ve been doing with this extension is experimenting with git and GitHub. I think it’s been an interesting experience, there are continual arguments over which is better between git and mercurial with many pros and cons listed. I think most of these were done some time ago before mercurial and git really matured because from what I’ve seen there is really little difference between the two. They have slightly different default branching styles, but both can do the same kind of branching that the other can if you want and there are a few other minor differences but nothing that would really make me all that bothered over deciding which to use. I think the only place where git has a bonus is with GitHub, and really as far as I can see there isn’t a reason why someone couldn’t develop a similar site backed by mercurial repositories, it’s just that no-one really has.

GitHub is pretty nice with built-in basic issue tracking and documentation though it still has some frustrating issues. It seems odd for example that you can’t fork your own project, only someone else’s, but that’s only a minor niggle really. As project hosting goes I can’t say I’ve come across anything better that I can remember.