Question

I have a Delphi 2009 program that handles a lot of data and needs to be as fast as possible and not use too much memory.

What small simple changes have you made to your Delphi code that had the biggest impact on the performance of your program by noticeably reducing execution time or memory use?

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Thanks everyone for all your answers. Many great tips.

For completeness, I’ll post a few important articles on Delphi optimization that I found.

Before you start optimizing Delphi code at About.com

Speed and Size: Top 10 Tricks also at About.com

Code Optimization Fundamentals and Delphi Optimization Guidelines at High Performance Delphi, relating to Delphi 7 but still very pertinent.

Answer 1

The biggest improvement came when I started using AsyncCalls to convert single-threaded applications that used to freeze up the UI, into (sort of) multi-threaded apps.

Although AsyncCalls can do a lot more, I’ve found it useful for this very simple purpose. Let’s say you have a subroutine blocked like this: Disable Button, Do Work, Enable Button.
You move the ‘Do Work’ part to a local function (call it AsyncDoWork), and add four lines of code:

var  a: IAsyncCall;    
a := LocalAsyncCall(@AsyncDoWork);  
while (NOT a.Finished) do 
  application.ProcessMessages;  
a.Sync;

What this does for you is run AsyncDoWork in a separate thread, while your main thread remains available to respond to the UI (like dragging the window or clicking Abort.) When AsyncDoWork is finished the code continues. Because I moved it to a local function, all local vars are available, an the code does not need to be changed.

This is a very limited type of ‘multi-threading’. Specifically, it’s dual threading. You must ensure that your Async function and the UI do not both access the same VCL components or data structures. (I disable all controls except the stop button.)

I don’t use this to write new programs. It’s just a really quick & easy way to make old programs more responsive.