Fanboy? Moi...?

See you back here in September!

So what’s been keeping me away from WordPress?

• Spending too much time in WinDbg tracking down .NET and COM memory issues.
• Wanting to have a good look at Visual Studio 2010 and .NET 4.0 (though not as much as I’d like, yet)
• Playing lots of Bayonetta, and some Heavy Rain.
• Doing lots of internal demos of the WPF\F# GUI-building toolset we’ve been working on. Should be interesting, specially now Luca’s coming on board.
• Experimenting with iPad development

Hopefully I’ll get the chance to write something about all of this soon.

This is such a common source of bugs, and such an important requirement, that from Vista onwards Microsoft introduced a new set of functions in the Windows API explicitly to support it: One-Time Initialization.

And even if you get away with doing naughty things in DllMain now, don’t think that it’ll stay that way forever. We got away with it for years, then when .NET came along it introduced all sorts of additional correctness checks. For instance, the Managed Debugging Assistant (MDA) in Visual Studio will shout loudly should you attempt to run managed code during DllMain.

Managed Debugging Assistant 'LoaderLock' has detected a problem in 'C:\YourApp.vshost.exe'.
Additional Information: Attempting managed execution inside OS Loader lock. Do not attempt to run managed code inside a DllMain or image initialization function since doing so can cause the application to hang.

And it’s easier than you think to do so. For example, calling something as innocuous as GetWindowText can result in managed code being run.

How can you get around this?

One of the approaches I’ve used has been to make use of Win32 asynchronous procedure calls. Specifically you can call QueueUserAPC to add a function to the queue, and this can contain the initialisation you would’ve otherwise done in DllMain.

However there is significant gotcha regarding use of APCs: your function will not be called until the thread is in an “alertable wait state”. This means you (or some other code on the thread) need to call an alertable wait function such as SleepEx, WaitForSingleObjectEx and specify TRUE for the alertable parameter.

Once your APC is getting called successfully you’ll be in much better place; your code will be executed outside of the scope of the dreaded OS loader lock and you’ll be doing things by the book, hopefully avoiding all the potential pitfalls that lie in wait within DllMain.

I had a look at the text of the first exception, and from that it was obvious:


Unable to cast COM object of type 'System.__ComObject' to interface type 'IWhatever'. This operation failed because the QueryInterface call on the COM component for the interface with IID '{CAD939D0-5E5D-11D7-AA0B-0002B33FE9DX}' failed due to the following error: Bad variable type. (Exception from HRESULT: 0x80020008 (DISP_E_BADVARTYPE)).


The message contains curly brackets around the IID, and they’re being intrepreted as insertion points by a call to String.Format!

Workaround

So that explained why it only happens in debugger runs; as this post helpfully points out the WPF databinding is enabled by default in that case. To workaround it, you can disable logging programmatically or using the App.config file to only display Critical output. So if your app is named foo.exe, create a file foo.exe.config that contains:

<configuration>

  <system.diagnostics>

    <sources>

      <source name="System.Windows.Data" switchName="SourceSwitch"/>

    </sources>

    <switches>

      <add name="SourceSwitch" value="Critical" />

    </switches>

  </system.diagnostics>

</configuration>

Fix…?

Hopefully there’ll be a fix for this at some point soon, as disabling the logging is a pretty large hammer to crack this small nut.

A couple of apologies are in order. Firstly, sorry if you tried to hit the site and found it down. I totally wasn’t prepared for the traffic; my bad. Secondly, sorry if you’ve posted a comment on the article here or elsewhere and I haven’t responded. I’m been swamped and the day job always seems to get in the way, dammit.

Anyway, thanks for reading, keep in touch, and I’ll try and get over that ‘difficult second album’ period I seem to be having.

After a bit of poking around, I came across this post. It points out the root cause of the problem is the PHP regular expression engine (PCRE) that Wordpress uses.

The easiest way to fix the problem is to ignore the advice in that post about modifying formatting.php, and instead make the fix to PHP.INI which is mentioned in the comments. I edited my copy to include the following line, which increases the backtracking limit from the default of 100000:

pcre.backtrack_limit = 1000000

After getting IIS to pick up the changes (iisreset) my missing content appeared again.

I’ve added a widget to the sidebar to give you a flavour.

Now, where’s that copy and paste…

• Preview window so you can easily check volume levels before recording
• Ability to pass recording settings on command line so you can use Windows Scheduler to record automatically at a certain time

It’s available here: http://www.opcode.co.uk/opd2d/default.asp

OpD2d has been downloaded about 5000 times a month for the past few years, and I’d like to take this opportunity to thank the people who’ve been generous enough to paypal me a few quid as thanks. This is much appreciated, and helps to keep me in t-shirts.