Friday, August 1, 2008

Structure Inlining with .Net 3.5 SP1

I just stumbled on a fascinating performance improvement coming up in .Net 3.5 SP1.

When working with value types (structs) the JIT currently hits the stack each time you access a field - which is quite inefficient.

In SP1 they've added an algorithm called "value type scalar replacement"; which intuitively does exactly what it sounds like!

Take the following code:
static int MyMethod1(int v)
Point point; // gets a stack location.

// All 3 field accesses involve stack operations.
point.x = v;
point.y = v * 2;

return point.x;

The JIT will replace the value type (Point is a struct) with scalars:
static int MyMethod2(int v)
int x; int y; // Was “struct point;”. Now replaced by x and y.
x = v;
y = v * 2;

return x;

After the JIT inlines the structure, it can optimise the routine by placing the integers on the register rather than the stack.

What's the difference?

We are roughly looking at a 10x improvement! (Using a quick and dodgy test app)

This is fantastic, especially when dealing with lots of structs like points and rectangles etc.

What's the catch?

This isn't magically going to work on all your value types; there are strict guidelines when this replacement can occur:

- The value type must have no more than 4 fields

- These fields must be value types, or object references

- You must use [StructLayout(LayoutKind.Sequential)], which is the default anyhow.

There some other catches, but if you are creating complicated structures, you really should think about making them a class.

More Improvements

This is just a snippet of the algorithm, whereas the original article explains it in much more detail.

BTW: This is in the CLR, so all .Net languages benefit! And of course this includes F# and FParsec.

Cheers to SP1!

Wednesday, July 23, 2008

Advanced Domain Model queries using Linq - Part IV

This should be the last part in my series of posts.  In this part I'll cover support for parameters via method calls.

Parameter Support (Contrived Example)

Continuing the Library example, how would you query the books that will be overdue next week?

Well you could write the following:
var nextWeek = from a in repository.AsQueryable()
where a.CheckOverdue(DateTime.Today.AddDays(7))
select a;

How it works

The CheckOverdue Property simply returns a Lambda Expression as it's result.
class CheckOverdueProperty : QueryProperty<Loan, Func<DateTime, bool>>
public CheckOverdueProperty()
: base(x => y => (x.DateReturned == null && (y - x.DateBorrowed).TotalDays > x.LoanPeriod))
{ }

I've modified the expression parsing routines to support parameters (including multiple) and even nested lambdas!

Nested Lambdas?

I can't really see the need for it, but hey... why not! Curry anyone? :)
class MyProperty : QueryProperty<Loan, Func<int, Func<int, Func<int, double>>>>
public MyProperty()
: base(a => x => y => z => x + y + z + a.LoanPeriod)
{ }

So how would you call such a monstrosity?
var test = from a in repository.AsQueryable()
select a.MyProperty(5)(4)(3);

But check out the SQL! Great work Linq to Sql guys!
SELECT (CONVERT(Float,5 + 4 + 3)) + [t0].[LoanPeriod] AS [value]
FROM [dbo].[Loan] AS [t0]

Declaration Syntax

If you're particularly astute, you'll have noticed that my syntax for declaring a QueryProperty has changed slightly since the last post.

Here's the class declaration of the CheckOverdue Property:
public bool CheckOverdue(DateTime date)
return CheckOverdueProperty.GetValue<CheckOverdueProperty>(this)(date);

Although this is a method, you can still define it as a property (notice that I return a lambda expression).
public Func<DateTime, bool> CheckOverdue
get { return CheckOverdueProperty.GetValue<CheckOverdueProperty>(this); }

So What's Changed?

Well, QueryProperties no longer derive from an Attribute class.  Although it worked, I felt dirty about it.

I borrowed from Fredrik's syntax and pass the property type to the Attribute - much cleaner.

Since I'm no longer defining the QueryProperty as static, I had to change the way it is referenced by the class property.

The code above shows my attempt at making this easy, yet efficient - but it's up to you how to implement it.  E.g. this would work well too:
public Func<DateTime, bool> CheckOverdue
get { return CheckOverdueProperty.Value(this); }

private static CheckOverdueProperty CheckOverdueProperty = new CheckOverdueProperty();

If you can think of better ways I'd love to hear it! 

Expression Parser

Since I posted the parser code in my last post, here it is again - and my has it grown!
class QueryPropertyEvaluator : ExpressionVisitor
// Basic member access support for QueryProperties
protected override Expression VisitMemberAccess(MemberExpression m)
if (m.Expression != null)
var property = GetProperty(m.Member);

if (property != null)
return Expression.Invoke(property.GetExpression(), m.Expression);

return base.VisitMemberAccess(m);

// Support method call abstractions over QueryProperties
// Assumes method call has same parameters (in order!) as QueryProperty
// Also supports static methods, as long as first parameter is the class object
protected override Expression VisitMethodCall(MethodCallExpression m)
Expression obj = this.Visit(m.Object);
IEnumerable<Expression> args = this.VisitExpressionList(m.Arguments);

var property = GetProperty(m.Method);

if (property != null)
if (obj != null)
// Method on QueryProperty class
return VisitLambdaInvocation(Expression.Invoke(property.GetExpression(), obj), args);
// Assumes static method where first parameter is object instance
return VisitLambdaInvocation(Expression.Invoke(property.GetExpression(), args.First()), args.Skip(1));

if (obj != m.Object || args != m.Arguments)
return Expression.Call(obj, m.Method, args);

return m;

// Support lambda expressions within QueryProperties
protected override Expression VisitInvocation(InvocationExpression iv)
IEnumerable<Expression> args = this.VisitExpressionList(iv.Arguments);
Expression expr = this.Visit(iv.Expression);

// Rewrite InvokeExpression - Folds out inner lambda
if (expr.NodeType == ExpressionType.Invoke)
return VisitLambdaInvocation((InvocationExpression)expr, args);

if (args != iv.Arguments || expr != iv.Expression)
return Expression.Invoke(expr, args);

return iv;

// Recursively 'flattens' the lambda invocation expressions
// Rewrites the nested lambda expression tree to work with Linq to SQL
protected Expression VisitLambdaInvocation(Expression expression, IEnumerable<Expression> args)
if (expression.NodeType != ExpressionType.Invoke)
return Expression.Invoke(expression, args);

var invoke = (InvocationExpression)expression;
var lambda = (LambdaExpression)invoke.Expression;

// Func<TClass, Func<Arg0, Arg1..., Result>> -> Func<TClass, Result>
var arguments = lambda.Type.GetGenericArguments().ToArray();
arguments[arguments.Length - 1] = arguments.Last().GetGenericArguments().Last();

return Expression.Invoke(
VisitLambdaInvocation(lambda.Body, args),

#region MemberInfo caching

private Dictionary<MemberInfo, QueryProperty> lookup = new Dictionary<MemberInfo, QueryProperty>();

// This is not strictly needed, but adds a performance improvement.
// Feel free to remove this code if you think memory is more important
protected QueryProperty GetProperty(MemberInfo info)
QueryProperty result = null;

if (lookup.TryGetValue(info, out result) == false)
var attribute = Attribute.GetCustomAttribute(info, typeof(QueryPropertyAttribute)) as QueryPropertyAttribute;

if (attribute != null)
lookup.Add(info, result = attribute.GetProperty());

return result;



As usual, here is the sample code for you to experiment with yourself.

I hope you've enjoyed this series, I certainly have. 

If I get the chance I might write a post explaining the expression parsing in detail, or the compiled queries - but till then...


Thursday, July 17, 2008

Advanced Domain Model queries using Linq - Part III

I didn't intend to post so quickly after my last post, but some comments from Nick motivated me to try something different.

So what's changed?

Not much.  Defining your query properties has changed (and obviously some implementation details).  All the linq syntax stuff stays the same.

Here's the same Loan class, rewritten:
class Loan
public decimal OverdueFee
get { return OverdueFeeAttribute.Property.GetValue(this); }

public bool IsOverdue
get { return IsOverdueAttribute.Property.GetValue(this); }

public double DaysOverdue
get { return DaysOverdueAttribute.Property.GetValue(this); }

And here's our query property definition:
class IsOverdueAttribute : QueryPropertyAttribute
public IsOverdueAttribute() : base(Property) { }

public static readonly QueryProperty<Loan, bool> Property = new QueryProperty<Loan,bool>(
x => (x.DateReturned == null && (DateTime.Now - x.DateBorrowed).TotalDays > x.LoanPeriod));

class OverdueFeeAttribute : QueryPropertyAttribute
public OverdueFeeAttribute() : base(Property) { }

public static readonly QueryProperty<Loan, decimal> Property = new QueryProperty<Loan, decimal>(
x => (decimal)(x.DaysOverdue * 0.45));

class DaysOverdueAttribute : QueryPropertyAttribute
public DaysOverdueAttribute() : base(Property) { }

public static readonly QueryProperty<Loan, double> Property = new QueryProperty<Loan, double>(
x => x.IsOverdue ? (DateTime.Now - x.DateBorrowed).TotalDays - x.LoanPeriod : 0);

What's the difference?

Well, depending on your programming tastes, it's cleaner.  We've reduced some of the tight coupling, and we now have the ability to spread the logic (which is more suitable in certain situations).

And if you're wondering why I seem to have an obsession with static members, it's mainly due to performance - and truth be told, I'm pre-optimizing here.  Generally I'm not such a fan... honest!

Performance anxiety

Speaking of performance, using Attributes has a penalty.  According to my tests, it's roughly 30% slower to parse the expression.  

This might sound like a lot, but we're talking about 0.37 vs 0.28 milliseconds per query here - and once you consider the database retrieval time... it's really nothing.

I don't even parse the expression tree with linq to objects - so no impact at all!

Bonus code (Expression Parser)

Here's my expression parsing code, I know you want to see it:
class QueryPropertyEvaluator : ExpressionVisitor
protected override Expression VisitMemberAccess(MemberExpression m)
if (m.Expression != null)
var attribute = Attribute.GetCustomAttribute(m.Member, typeof(QueryPropertyAttribute)) as QueryPropertyAttribute;

if (attribute != null)
return Expression.Invoke(attribute.Property.GetExpression(), m.Expression);

return base.VisitMemberAccess(m);

Beautiful isn't it!

Feedback please

If you've been following this little series, I'd love to hear what you think of the new syntax.

I'm still hesitant, since this new syntax results in more code - but I think it's a cleaner approach.

As usual, you can find the sample app here - enjoy!

Wednesday, July 16, 2008

Advanced Domain Model queries using Linq - Part II

Since my previous post I've rewritten the internals to make use of LinqKit - a fantastic lightweight project.

See the changes

I took my rewrite as an opportunity to support the full query syntax:
var overdue = from a in repository.AsQueryable()
where a.IsOverdue == true
select a.OverdueFee;

var days = repository.AsQueryable()
.Where(x => x.IsOverdue)
.Select(x => x.DaysOverdue);

and added easy support for compiled queries (currently only supporting linq to objects and linq to sql):
var query = repository.Compile(
source => from x in source
where x.IsOverdue == true
select x.OverdueFee);

var results = repository.Execute(query);

I've also optimized the expression parsing (speed difference is negligible to normal queries), and I tweaked the QueryProperty construction:
#region IsOverdue Property

public bool IsOverdue
get { return IsOverdueProperty.GetValue(this); }

static public readonly QueryProperty<Loan, bool> IsOverdueProperty = new QueryProperty<Loan, bool>(
x => x.IsOverdue,
x => x.DateReturned == null && (DateTime.Now - x.DateBorrowed).TotalDays > x.LoanPeriod);


The big change here is that I've added an extra parameter; a reference back to the mapping property.

I'd really like a memberof(Loan.IsOverdue) keyword style syntax in C#, but since there's not, I use this expression to grab the MemberInfo - which is used in the expression parser.

It's a slight DRY drawback, but it's a faster way than using reflection (and avoids an ugly string lookup) - and it's much faster than using attributes.

Get the code

Most of the big changes are all implementation specific, so be sure to check out the sample app.

Please let me know what you think!

BTW: Joseph, I made some architectural changes to the LinqKit.ExpandableQuery stuff.  Externally it behaves exactly the same, but it now lets me reuse a lot more code.

It's light on the comments, but I'm hoping my next post will explain myself.

ed: Continue to Part III

Tuesday, July 15, 2008

Ctrl . - My favourite shortcut

I'm a huge keyboard shortcut fan (for a windows developer)... for common tasks it's just annoying to have to grab the mouse.

For me, one such task was the rename / resolve support in Visual Studio:unresolved 
Using the mouse to bring up this dialog has got to be the most frustrating task in Visual Studio.

So much so, I refused to use it; instead opting for the right-click 'resolve' approach, or even manually typing in namespaces.


A few months ago, I stumbled on "Ctrl ." and to my delight ended my coding frustration.

I'm now more productive, less frustrated... do yourself a favour and give "Ctrl ." a go!

Monday, July 7, 2008

Advanced Domain Model queries using Linq

I read a fantastic blog article from Nick Blumhardt yesterday which kicked off some crazy ideas in my head.

The Problem

With the following class, I can query on IsOverdue using linq... but not using linq to sql (or linq to nhibernate).  How frustrating!
class Loan
// Member details omitted
public bool IsOverdue
return DateReturned == null &&
(DateTime.Now - DateBorrowed).TotalDays > LoanPeriod;

This is a fundamental issue in relational to object mapping systems, but we can fix it using some linq trickery.


I think my solution is very cool, but I'm not sure how acceptable it is for a production environment. 

Please leave feedback if you like it / makes you want to vomit.

The change

Let's modify the Loan class implementation of IsOverdue:
#region IsOverdue Property

public bool IsOverdue
get { return IsOverdueProperty.GetValue(this); }

static public readonly QueryProperty<Loan, bool> IsOverdueProperty = QueryProperty.Register<Loan, bool>(
x => x.DateReturned == null && (DateTime.Now - x.DateBorrowed).TotalDays > x.LoanPeriod);


Here we move the logic for IsOverdue into a separate QueryProperty member that takes care of the nasty details.

Hopefully you'll agree that the code is still fairly readable, and encapsulated with all the logic still bundled inside the Loan class.

By moving this logic into a lambda expression, we can now write queries for both database and object collections! e.g
// Database Access
using (var db = new RepositoryDatabase<Loan>())
var overdue = db.Where(y => y.IsOverdue && y.LoanPeriod == 5);

// Collection Access
using (var list = new RepositoryCollection<Loan>())
var overdue = list.Where(y => y.IsOverdue && y.LoanPeriod == 5);

More Goodness

When coding these query properties it can be very handy to reference other query properties. e.g.
#region DaysOverdue Property

public double DaysOverdue
get { return DaysOverdueProperty.GetValue(this); }

static public readonly QueryProperty<Loan, double> DaysOverdueProperty = QueryProperty.Register<Loan, double>(
x => x.IsOverdue ? (DateTime.Now - x.DateBorrowed).TotalDays - x.LoanPeriod : 0);


#region OverdueFee Property

public decimal OverdueFee
get { return OverdueFeeProperty.GetValue(this); }

static public readonly QueryProperty<Loan, decimal> OverdueFeeProperty = QueryProperty.Register<Loan, decimal>(
x => (decimal)(x.DaysOverdue * 0.45));


This allows us to create very complicated queries in a very simple manner.

The Catch

Too good to be true?  You're right; there's a devil in the details. 

You might have picked it up already - how does linq interpret my query property correctly?

By modifying the expression tree!

My Repository class implements the Where() and translates the expression; replacing any QueryProperty references with a call to the actual lambda expression.

The really ugly part is that it's a string based lookup ie. "<name>Property".  Though I also check the type to be extra safe.

It's really not a bad trade off, considering it's very similar to how WPF DependencyProperty's work.

The Conclusion

This is a really easy and seamless way to implement custom queryable properties in your domain objects.

I've only touched on a fraction of the possibilities with this technique, but it shows the power and flexibility of linq.

Make sure you check out the sample application for the full code.

ed: Continue to Part II

Friday, June 27, 2008

Loop optimization trickery

A while ago I was playing around with C# 3.5 lambda expressions trying to work out how it behaves with variable scope.

What do you think is written to the console?
class Program
static void Main(string[] args)
// Write number to console in worker thread
for (int i = 1; i < 9; i++)
DoLater(() => Console.Write(i));

// Call action delegate on separate thread
static void DoLater(Action action)
// I'm avoiding using another lambda here to simplify test
new Thread(new ParameterizedThreadStart(DoLater)).Start(action);

// Calls the action after waiting for a second
static void DoLater(object action)

If you initially guessed (like me) that it displays the numbers 1-9 in some random order (eg. '14385726') - you'd be wrong...   it actually produces '999999999' every time.

So I cranked up .net reflector (I love it) and had a look at my code (optimization set to .NET 1.0 - then translated by me):
private static void Main(string[] args)
AutoDelegateClass tmpVar = new AutoDelegateClass();
tmpVar.i = 1;
while (tmpVar.i < 9)
DoLater(new Action(tmpVar.Method));

This is much more obvious...  .net optimizes the lambda expression out of the loop!

Well that was unexpected, but guess what happens when I change main to this:
static void Main(string[] args)
for (int i = 1; i < 9; i++)
int j = i;
DoLater(() => Console.Write(j));

This works! ie. it does not optimize the lambda expression out of the loop.

Although confusing at first, it actually makes a lot of sense from the compiler point of view - the initial expression doesn't actually change, since we are referencing a mutable variable... so why not optimize it?

It might be convenient to turn off this optimization programmatically - kind of like a volatile keyword or something, but it's no big deal.

I guess it goes to show that functional code works best with immutable data... and that reflector is way cool.

BTW: The exact same thing occurs in foreach over a collection; and also using classes rather than structs.

Monday, June 23, 2008

UI - You don't know how much you suck

I made a small mistake in my last post - instead of 'do what you want' what I meant to say was:

Hire a damn graphic designer and buy some icons!

This is a subtle difference, but the delusion of competency is unfortunately common.m-diy-disaster

Like your home handyman disasters, the DYI attitude for user interfaces can cost you big time.

However IT departments are usually too cheap, and some developer ego's are too big to realize that they can't do everything... thus UI abominations are created everyday.

UI development is hard, harder than most people think. 

The UI layer is where everything comes together, and as a result it's here you find all the issues with the underlying architecture.

If you're a UI developer - you suck, so make sure you check out the UI guidelines for your dev system (Microsoft, Apple, Gnome or KDE).

If you're not a UI developer; shut up, fix your code and give the UI guys a break.

Oh, and good luck!

Disclaimer: I've done both jobs, so I suck twice as much.

Tuesday, April 22, 2008

UI - You can't please everyone

Although it's difficult to create good UI, it doesn't mean that bad UI is easy - in fact some people go to great lengths to produce bad UI.

That said, good UI simply boils down to:

Intuitive, Pretty and Performant - in a combination that targets the intended user.

eg. A programmer is going to prefer performance over pretty, and a hairdresser might prefer pretty over intuitive... but you still need all three for a good user experience.

If you don't have access to your user (and that's generally the case), just pretend that you are the user.

If you wouldn't use your own app; that's a good sign of bad UI.

In the end, you can't please everyone - so please yourself, then at least one person is happy.

Wednesday, February 20, 2008

Six Percent Genius

Project Euler (pronounced "Oiler") provides a number (~182) of challenging math/programming problems... which is a fantastic environment to play with F#!

I've only completed 6% of the questions but I've already learnt a lot. (F# is huge)

If you have some free time (or get bored during your compiles), I'd definitely recommend having a go - in your own language of choice of course!

Tuesday, January 15, 2008

Deriving Miss Daisy

As I've mentioned previously, I'm slowly reading through SICP - it's an amazing book and reading it has been a humbling experience.

'Geeking' Out

I completely geeked out reading one example on functional derivatives.  (Take a math expression as a parameter and return the derivative as an expression)

It's in the first chapter, and they use this to implement Newton's Method -> to then implement a Sqrt function!

Approximate Derivative

After I picked my brain off the floor, I decided to have a crack at implementing derivatives in C# using lambda expressions:


Using the formula of a derivative (above), we can simply code an approximate derivative (below):

Func<double, double> Approximate(Func<double, double> f)
var h = 0.0001;
return a => ((f(a + h) - f(a)) / h);

Symbolic Derivation

Easy huh!  So for fun I decided to use linq expression trees to derive algebraically.

It's easy to get an expression tree in C# - simply use the Expression<> type.
Func<double, double> Derive(Expression<Func<double, double>> e)
var lambda = new Derivative().Eval(e) as LambdaExpression;
return (Func<double, double>) lambda.Compile();

I parse the expression tree using Matt Warren's ExpressionVisitor class - and using the basic rules of Derivation (Constant, Product and Quotient rules) we get:
class Derivative : ExpressionVisitor
public Expression Eval(Expression exp)
return this.Visit(Evaluator.PartialEval(exp));

protected override Expression VisitBinary(BinaryExpression b)
// Product Rule: (fg)' = f'g + fg'
if (b.NodeType == ExpressionType.Multiply)
return Expression.Add(
Expression.Multiply(Eval(b.Left), b.Right),
Expression.Multiply(b.Left, Eval(b.Right)));

// Quotient Rule: (f/g)' = (f'g - fg') / (g*g)
if (b.NodeType == ExpressionType.Divide)
return Expression.Divide(
Expression.Multiply(Eval(b.Left), b.Right),
Expression.Multiply(b.Left, Eval(b.Right))),
Expression.Multiply(b.Right, b.Right));

return base.VisitBinary(b);

// Parameter Derivation: f(x)' = 1
protected override Expression VisitParameter(ParameterExpression p)
return Expression.Constant(1.0);

// Constant Rule f(a)' = 0
protected override Expression VisitConstant(ConstantExpression c)
return Expression.Constant(0.0);

Wrapping it up

To quickly finish this long blog post, here's the usage code:
// f(x * x * x)' = 3 * x * x
var approx = Approximate(x => x * x * x);
var derive = Derive(x => x * x * x);

var y1 = approx(1); // 3.0000300001109532
var y2 = derive(1); // 3.0

And there it is!  Useful? maybe not.  Fun? Definitely!

Monday, January 7, 2008

The 'Y' in Blog

It's quite demoralizing when you consider how much you don't know. I am continually reminded that I underestimate it's sheer quantity... it's a sad realization.

Since there is so much already written by people more knowledgeable and intelligent than myself, why do I write?

Well, I started this blog to show my appreciation, and hopefully to contribute something back to the development community.

So kudos to all of you... keep sharing the love (of maths & programming)!

Associate with people who are searching for answers, avoid those who have found them.

Happy New Year!