32-bit client can’t connect to 64-bit COM server

March 10th, 2010 by Andy No comments »

In a previous post I described how to host a COM server in a managed process using RegistrationServices.RegisterTypeForComClients.  I’ve been using this approach successfully for a while, but today I hit a snag.   I changed my C# server process from 32-bit to 64-bit, and immediately my 32-bit C++ client could no longer connect.

In theory it shouldn’t matter to the client whether the server is 32-bit or 64-bit – everything is out-of-process so there is no compatibility issue.   But I could see that COM was refusing to allow my client to connect to the running 64-bit server process, and instead was trying to launch a new server process (which was failing because I don’t allow that).

I have seen this type of problem many times before with COM, and it’s almost always due to security configuration – specifically the ‘run as’ configuration of the server.   So I spent a lot of time investigating that, but it turned out to be something much simpler.  Since Windows 2003 SP1, COM has a rule on x64 that if a 32-bit client CoCreates an out-of-proc server, COM will try to connect to a 32-bit server.  If the client is 64-bit, COM will try to connect to a 64-bit server.  So in my case, COM could see that the 64-bit server was running, but because the client was 32-bit it decided to launch a new (hopefully 32-bit) server process to service the request.

Fortunately there are two easy ways around the problem.  The first option is to modify the client to specify  CLSCTX_ACTIVATE_64_BIT_SERVER in the CoCreateInstance call.  The other (probably better) option is to add a PreferredServerBitness flag to the AppID registry entry for the server.

CLSCTX_ACTIVATE_64_BIT_SERVER is described here, and PreferredServerBitness here.

Debug mode on the Pentax K20D DSLR

January 5th, 2010 by Andy 6 comments »

I really like my Pentax K20D DSLR, but when I first got it the autofocus was not accurate, particularly with my favourite FA 50mm 1.4 lens.   Fortunately the camera has an autofocus adjustment in the standard menu, which fixed the problem, but I recently discovered that there is a hidden ‘debug’ menu that offers even more control over autofocus.   However the procedure to turn on the debug menu is a little fiddly, so I thought I’d document it here.

[Note that these instructions only apply to the K20D.   Other Pentax and Samsung cameras also have a debug mode, but the instructions are slightly different for each camera – see the end of the post for links.]

Step 1: Create a text file called MODSET.442 in the root of your SD card.   The file should contain the following single line:


You can use any plain text editor, for example Windows Notepad.  Make sure that the file is called MODSET.442 and not MODSET.442.txt

Step 2: Put the SD card into the camera but leave the card door open.

Step 3: Hold down the Menu button and turn on the camera.  Keep holding down the Menu button until the debug menu appears.


Step 4:  Close the SD card door.

Step 5: To enable debug mode, press the right arrow to change Debug Mode from DIS to EN, then press the OK button.


Step 6: Press the MENU button to get to the standard camera menu.   (If nothing happens, make sure you have closed the SD card door.   If necessary, turn the camera off and on again after closing the door.)

Press the right arrow twice to get to the Setup menu:


This is just the standard Setup menu, but some new items have been added to the bottom.  Press the up arrow to quickly jump to the bottom to see them.


Select AF TEST then click the right arrow button.


You can now set the global focus correction.  In this screenshot the correction is set to –90 and I am about to increase it by 20 (making it –70).   Press the OK button and you are ready to take a test shot with your new AF setting.  (Some reports suggest that the camera must be restarted after setting the correction value, but it seems to apply immediately on my camera.)

Step 7:  Once you have finished playing with the AF correction, you will want to turn off the debug menu.  To do so, just turn the camera on and when the debug menu appears, set DEBUG MODE to DIS and click OK.   Your camera should now be totally back to normal.

You can leave the MODSET.442 on your SD card and then re-enable the debug menu at any time by starting from step 2.  Or you can just delete the file if you prefer.

If some part of the instructions doesn’t seem to be working, check your SD card door.   For some steps it must be open, and others it must be closed – follow the instructions exactly as above.

The debug menu is also available on several other Pentax and Samsung cameras – see the pentax-hack site for details.

Also there are detailed instructions for the Pentax K-x here, which I found very useful, even though the steps are slightly different than the K20D.

After many many test shots I think I’ve settled on –90 as my correction value.   That allows me to run my FA 50mm 1.4 with no ‘standard’ correction, and my other lenses seem happy too.

Using ANTLR to parse boolean queries

December 23rd, 2009 by Andy 1 comment »

ANTLR is a well-known parser generator.  You supply it with a grammar and it builds a lexer and parser in the programming language of your choice.   I’ve just spent a few hours getting to grips with ANTLR basics, so I thought I’d document it for future reference.

My basic requirement is to transform an end-user boolean query to an XML document.   A simple example of a query I need to parse is:

john AND (joe OR sue)

I want the generated parser to produce the following syntax tree for this query:


It should then be trivial to walk the tree and write the XML document I need.

An ANTLR grammar is specified in a text file with a .g extension.   Here’s how my SimpleBoolean.g starts:

grammar SimpleBoolean;

  language = CSharp2;
  output = AST;

I’m specifying that the generated code should be C#, and that the parser should build an abstract syntax tree (AST).

Next I specify the lexer rules:

LPAREN : '(' ;
RPAREN : ')' ;
AND : 'AND';
OR : 'OR';
WS :  ( ' ' | '\t' | '\r' | '\n') {$channel=HIDDEN;}  ;
WORD :  (~( ' ' | '\t' | '\r' | '\n' | '(' | ')' ))*;

These rules are used to turn the source text into a stream of tokens.  So parentheses and operators are special tokens, and anything else is either whitespace (which is skipped) or a word.

Finally I specify the parser rules:

expr : andexpr;
andexpr : orexpr (AND^ orexpr)*;
orexpr : atom (OR^ atom)*;
atom : WORD | LPAREN! expr RPAREN!;

This is the confusing bit.  The chain of expressions (expr –> andexpr –> orexpr) is used to signify precedence.  In this case I’ve made OR higher precedence than AND.   Also notice that andexpr (for example) does not require an AND – it is optional.  This is why the grammar supports an expr containing only an OR, even though expr is defined in terms of andexpr.

The symbol suffixes (^ on the operators and ! on the parentheses) are there to direct the AST generation.  ^ signifies a tree branch, whereas ! indicates something that should be omitted from the tree.   Anything else is a leaf.   (The parentheses are omitted because they are redundant – the structure of the tree gives the order of evaluation implicitly.)

So SimpleBoolean.g is now complete, and all that remains is to ask ANTLR to generate a C# parser from it.  I used the ANTLRWorks IDE for this, but you could use the command-line.   Once the C# files are generated, and the ANTLR .NET runtimes files added to a C# project, we’re ready to write some C#.   Here’s some code that parses a query and then walks the syntax tree and writes the nodes to the console:

class Program
    static void Main(string[] args)
        ANTLRStringStream expression = new ANTLRStringStream("john AND (joe OR sue)");
        var tokens = new CommonTokenStream(new SimpleBooleanLexer(expression));
        var parser = new SimpleBooleanParser(tokens);

        SimpleBooleanParser.expr_return ret = parser.expr();
        CommonTree ast = (CommonTree)ret.Tree;

    static void Print(CommonTree tree, int level)
        Console.WriteLine(new string('\t', level) + tree.Text);
        if (tree.Children != null)
            foreach (CommonTree child in tree.Children)

which prints the following:


For a more comprehensive ANTLR tutorial, see this series of blog posts.