In the previous installment I introduced the idea of a readers-writer lock. Today I'll look into readers-writer lock implementations (yes, multiple) that are available in the Delphi run-time library.
The Delphi Geek
random ramblings on Delphi, programming, Delphi programming, and all the rest
Tuesday, December 08, 2020
Sunday, November 08, 2020
Readers-writer lock - Part 1: Why?
One of the pleasant surprises in Delphi 10.4.1 was the addition of a new readers-writer lock implementation TLightweightMREW. While it was probably not noticed by most of the users, I was quite happy to see it implemented.
So now you are asking yourself - what is this readers-writer lock and why am I so happy to see it in Delphi? Well, I'm glad that you're asking! Let me explain ...
In multithreaded programming (as most of my horror stories start), we frequently run into a problem of resource sharing. Two threads want to modify a shared resource at the same time and that can cause many problems, from information being overwritten to corrupted data and program crashes.
To fix this, we add resource protection. Usually that is just a critical section (typically through a TCriticalSection wrapper), or Delphi's TMonitor. Sometimes, however, protecting resources with a simple critical section causes an unnecessary performance drop, and that's when a readers-writer lock (may) come into play.
Saturday, May 30, 2020
OmniThreadLibrary 3.07.8
Version 3.07.8 is mostly a bugfix release. It fixes few small bugs and enables support for Delphi 10.4.
You can get it now on git, download the ZIP archive, install it with Delphinus or with GetIt (in few days).
For more information, visit OmniThreadLibrary home page or write your question on the forum.
Wednesday, May 27, 2020
Top three Delphi 10.4 features
Friday, February 14, 2020
Long live Delphi!
Friday, November 29, 2019
Sales! Sales! Sales!
Parallel Programming with OmniThreadLibrary
printed book: 25% off (use coupon BLACKFRIDAY25)
Delphi High Performance
Hands-on Design Patterns with Delphi
Friday, November 08, 2019
ITDevCon X
Monday, September 30, 2019
CompareValue for booleans
CompareValue function is incredibly practical when you are writing comparers (functions that determine how some data structure is ordered). System.Math and System.StrUtils define a bunch of functions that can be used to compare integers, doubles, strings … There’s, however, no CompareValue for booleans.
A CompareValue function compares two parameters, traditionally named left and right, and returns 0 if they are the same, –1 if left is smaller and 1 if right is smaller.
If we use the usual ordering of false < true, we can write the missing function as follows:
function CompareValue(left, right: boolean): integer; overload; begin if left < right then Result := -1 else if left > right then Result := 1 else Result := 0; end;
Your task for today – if you choose to accept it – is: Write this function without any if statements.
Thursday, September 12, 2019
Visit “What’s new in Rio 10.3.2” in Ljubljana
On September 26th I’ll talk about RAD Studio Rio in Ljubljana. We’ll discuss 10.3 a bit and 10.3.1/10.3.2 updates in more detail. We’ll also look into the future to see what 10.4 might bring.
This will also be a good opportunity to see my latest book, Design patterns with Delphi, or get your own copy signed.
Participation is free, but you should register here so we can prepare enough food for everyone.
Tuesday, July 16, 2019
When True is not
Writeln ( True); Magic;Writeln ( True);
… output this:?
TRUE FALSE
Simple!
Tuesday, July 02, 2019
The case of a missing begin/end
Did you know that this is a valid syntax?
case a of
0: Writeln(0);
else
Writeln('else');
Writeln(a);
end;
This code indeed compiles and works exactly as the following fragment.case a of
0: Writeln(0);
else begin
Writeln('else');
Writeln(a);
end;
end;
I personally would never drop begin/end inside a case/else statement, but at least someone must disagree. I found such example in a very (VERY!) old code (it was written for Delphi 2) and I was quite surprised that it compiles at all.EDIT
Anton Alisov suggested formatting first example as:
case a of
0: Writeln(0);
else
Writeln('else');
Writeln(a);
end;
I guess this makes more sense (but just an itsy bitsy teenie weenie bit more).Thursday, June 06, 2019
Monday, April 29, 2019
Spring4D European Conference 2019 sessions
Slides and code for the Spring4D conference are now published on the conference page.
Slides and code for my two sessions – Design patterns with Spring4D and Interception and dynamic proxy – are also available on my presentations page.
Saturday, April 27, 2019
FastMM4 large memory allocation–benchmarking VirtualAlloc
TLThere were, however, other interesting results that my simple benchmark pointed out. More on that in a moment, but first…; DR Yes, allocating from the top is slower. No, the difference is not big and in most cases you’ll not even notice it.
Thursday, April 18, 2019
Books, books, books
You probably know that I write books. A big part of making a book, however, is not just writing it, but letting all the potential readers out there know that the book exists. I'm doing a lot there - and so is my publisher - but still we can't reach all the potential readers ourselves.
That's where you come in!
If you have read any of my books and if you loved it and want the others to know, please consider publishing a review on the Amazon site. More reviews make Amazon algorithms treat the book with more respect and they recommend it more to customers.
Leave the review here: Delphi High Performance, Hands-on Design Patterns with Delphi.
You can also just tell your colleagues in any social circle - digital or real-life - that you like the book. Spread the word!
If you think that is too much and you don't want to get involved so deep, it doesn't matter. I still love you.
Thank you,
Primož
Monday, April 08, 2019
Deep Dive into Design Patterns
While writing Design Patterns with Delphi, I spent quite some time researching existing literature on design patterns implementation in Delphi, design patterns in other languages, other types of patterns, design principles and so on …
In case you would like to dig deeper than the book takes you, here is my reading list.
Tuesday, March 26, 2019
Spring conference, spring edition

It’s
You can join us for a day or two. Your call, but I would
“Bee there Orr Bee A Rectangular Thyng
”
- The Band With Rocks In *
Friday, March 08, 2019
Delphi developer needed (Slovenia)
Slovenian company BASS is looking for a Delphi developer (on-site in Celje, Slovenia).
(I’m not affiliated with them; they just asked me to spread a word around. If you have any questions, contact them directly.)
Wednesday, February 27, 2019
Design Patterns with Delphi (book)
Hurrah, hurray, my third book is here! It’s called Hands-On Design Patterns with Delphi and (just like my first book) I wrote it for Packt Publishing. (The second book was self-published and I expect the fourth one to be, too.)
As the name says, “Design Patterns with Delphi” deals with design patterns. It is a bit different from most of design pattern books and websites you will find on the Internet. Case in point A: There are no UML diagrams. I don‘t speak UML. Tried to learn it few times but for some reason the whole concept doesn‘t agree with me. If you like diagrams, don’t fear though. Any book on design patterns - and most websites covering that topic - will gladly show how any design pattern can be diagrammed. That, however, is not important and should not govern your decision to buy the book.
More important is case in point B: This book speaks Delphi. All the examples are written in Delphi and language features are used to the full. I also covered few less known Delphi idioms in separate sections. You’ll still be able to follow the discussion even though you may program in a different Pascal dialect.
There’s also case in point C: Examples make sense. I deeply dislike classical design pattern examples of the “And then we want to write this program for different toolkits and it should also be able to draw circles, not only squares” kind. Euch! I tried to find a good example for each design pattern. Admittedly, I ended with few examples that draw triangles and squares on screen (mostly because some patterns were designed specifically for solving such problems), but most of them are of a more practical nature.
This book covers all three classical design pattern categories - Creational patterns, Structural patterns, and Behavioral patterns. It also discusses patterns from the newer Concurrency patterns category. At the end I threw in some borderline-pattern(ish) topics and ended with a discussion of few patterns that cannot be strictly classified as “design” patterns.
In this book you’ll find:
- Chapter 1
An introduction to patterns. Exploration of design principles, design patterns, and idioms. A mention of anti-patterns. A short description of most important design principles. Delphi idioms: creating and destroying objects. - Chapter 2
Creation patterns part 1. Singleton. Dependency injection. Lazy initialization. Object pool. - Chapter 3
Creation patterns part 2. Factory method, Abstract factory, Prototype, Builder. Delphi idioms: Assign and AssignTo. - Chapter 4
Structural patterns part 1. Composite. Flyweight. Marker interface. Bridge. Delphi idioms: comparers and hashers. - Chapter 5
Structure patterns part 2. Adapter. Proxy. Decorator. Facade. Delphi idioms: replacing components in runtime. Also: helpers. - Chapter 6
Behavioral patterns part 1. Null object. Template method. Command. State. - Chapter 7
Behavioral patterns part 2. Iterator. Visitor. Observer. Memento. Delphi idioms: for .. in. - Chapter 8
Concurrency patterns part 1. Locking. Lock striping. Double-checked locking. Optimistic locking. Readers-writers lock. Delphi idioms: tasks and threads. Also: bitwise operators. - Chapter 9
Concurrency patterns part 2. Thread pool. Messaging. Future. Pipeline. - Chapter 10
Writing Delphi programs. Event-driven programming. Actions. LiveBindings. Form inheritance. Frames. Data modules. - Chapter 11
Wrapping it up. Exceptions. Debugging. Functional programming.
I hope you will like this book and learn a lot from it. I know I did during the nine months I spent writing it. And if you find any bug in the code, let me know so I can correct it in the second release!
Saturday, February 23, 2019
OmniThreadLibrary 3.07.7
New OmniThreadLibrary is out! Get it while it’s hot!
Version 3.07.7 is mostly a bugfix release. It fixes a stupid mistake introduced in version 3.07.6 plus some other minor bugs.
You can get it now on git, download the ZIP archive, install it with Delphinus or with GetIt.
For more information, visit OmniThreadLibrary home page or write your question on the forum.
Tuesday, January 29, 2019
Caching with class variables
Tuesday, November 27, 2018
RAD Studio 10.3 Rio in Slovenia
On December, 6th I’ll be showing all that is new and shiny in 10.3 Rio to anyone that happens to pass by!
Join me in Ljubljana at 9:30 in the “standard” venue … just don’t forget to register first.
Monday, November 26, 2018
OmniThreadLibrary 3.07.6
Version 3.07.6 brings official support for Delphi 10.3 Rio, few changes and bugfixes.
You can get it now on git, download the ZIP archive, install it with Delphinus or with GetIt.
For more information, visit OmniThreadLibrary home page or write your question on the forum.
Tuesday, November 20, 2018
For..to..step in Delphi!
Today I was porting some legacy code and noticed a weird warning:
Weird warning, I thought. Obviously the loop variable can be passed as a var parameter as the code compiles. Why a warning and not an error, then?
Thursday, November 08, 2018
Using configuration records and operators to reduce number of overloaded methods
When writing libraries you sometimes want to provide users (that is, programmers) with a flexible API. If a specific part of your library can be used in different ways, you may want to provide multiple overloaded methods accepting different combinations of parameters.
For example, IOmniPipeline interface from OmniThreadLibrary implements three overloaded Stage functions.
function Stage(pipelineStage: TPipelineSimpleStageDelegate;
taskConfig: IOmniTaskConfig = nil): IOmniPipeline; overload;
function Stage(pipelineStage: TPipelineStageDelegate;
taskConfig: IOmniTaskConfig = nil): IOmniPipeline; overload;
function Stage(pipelineStage: TPipelineStageDelegateEx;
taskConfig: IOmniTaskConfig = nil): IOmniPipeline; overload;
Delphi’s own System.Threading is even worse. In class TParallel, for example, there are 32 overloads of the &For class function. Thirty two! Not only it is hard to select appropriate function; it is also hard to decode something useful from the code completion tip. Check the image below – can you tell which overloaded version I’m trying to call? Me neither!
Because of all that, it is usually good to minimize number of overloaded methods. We can do some work by adding default parameters, but sometimes this doesn’t help. Today I’d like to present an alternative solution – configuration records and operator overloading. To simplify things, I’ll present a mostly made-up problem. You can download it from github.
Wednesday, June 20, 2018
Delphi - always full of surprises!
IOW, following two lines do exactly the same:
s := Copy('123456789', 4, 6);
s := Copy('123456789', 4);
Works for arrays, too!
Of course, this is not documented.
Sunday, May 20, 2018
Introducing MultiBuilder
Typically I develop new stuff on Berlin or Tokyo and then occasionally start a batch script that tests if everything compiles and runs unit tests for all supported platforms in parallel. (I wrote about that system two years ago in article Setting Up a Parallel Build System.) Dealing with 14 DOS windows, each showing compilation log, is cumbersome, though, and that's why I do this step entirely too infrequently.
For quite some time I wanted to write a simple framework that would put my homebrew build batch into a more formal framework and which would display compilation results in a nicer way. Well, this weekend I had some time and I sat down and put together just that - a MultiBuilder. I can promise that it will be extensively used in development of OmniThreadLibrary v4. (Which, incidentally, will drop support for 2007 to XE. You've been notified.)
The rest of this post represents a short documentation for the project, taken from its GitHub page.
I don't plan to spend much time on this project. If you find it useful and if you would like to make it better, go ahead! Make the changes, create a pull request. I'll be very happy to consider all improvements.
Monday, May 14, 2018
See you in Piacenza!
On June, 6th I'll lead a seminar titled Writing High Performance Delphi Applications. It will be based on material from my Delphi High Performance book. We will look into variety of topics - algorithmic complexity, performance considerations when using built-in Delphi types, memory manager internals and optimisations and parallel programming. This will also be a good chance to grab a signed copy of the "high performance" and Parallel Programming with OmniThreadLibrary books (wink, wink ;) ).
Next day I'll participate on the conference programme with a talk called Defensive programming for a better future. Without even starting Delphi (look ma, no hands!) I'll look into different areas of programming where some common sense and simple guidelines can represent a difference between well- functioning code and a nest of bugs.
See you!
Wednesday, April 25, 2018
Multithreading is (still) hard!
No matter how long you deal with it and how good you (think) you are, you will make a mistake. Usually, it will be a problem that will only exhibit itself in a rare circumstances, most probably on a hard-to-reach customer machine. With some (bad) luck it will only appear on Friday afternoons or during your vacation.
That is why I'm always introducing multithreading with the "Don't do it yourself!" motto. Use a standard library! (And by that I mean OmniThreadLibrary, of course. ;) ) As your code, it too will have bugs. Unlike your code, it has 1000+ users running it in very different environments which means that at least it is tested as much as possible.
There are, nevertheless, bugs that escape detection for a long time. In 2011, for example, I fixed a well-hidden problem in TOmniBlockingCollection ("Multithreading is Hard!"). As nasty as that was, it was nothing compared to the bug I found recently!
As it turned out, the implementation of a bounded (fixed-size) multiple-producer multiple-consumer lock-free queue TOmniBoundedQueue (try saying that in one breath!) was buggy since its inception! As this queue is basis to all OmniThreadLibrary communication channels it is really surprising that the bug hid from everybody for 9 (yes, nine!) long years.
Friday, March 02, 2018
Delphi High Performance
Last year they published Expert Delphi by Paweł Głowacki, followed this year by my book and (as I have it on a good authority) at least one more. All books are available in electronic and printed formats. They also offer Delphi video lectures.

Writing a book that tells you "this is how you make your algorithm faster" is, sadly, impossible. That's why we consultants are for ;) In the book I only gave few advises (with lots of examples) about working with the GUI and about caching results from calculations.
Only then do I go deep into Delphi. Writing fast applications means knowing how built-in data types behave. I look into data life-cycle, what happens when a data of some type is modified and how it is passed in function calls. The life-cycle part cannot be explained without talking about memory which brings in a discussion of memory managers in general and FastMM in specifics.
Only then does the book introduce multithreading. Whole three chapters are dedicated to it and one of them is specifically written to show you why multithreading is hard, what you should never do when writing multithreaded code and why you shouldn't approach this topic with a preconception that it will automatically speed up your code. Only then do I introduce TThread and modern concepts such as tasks, futures, parallel for and so on. Most of the time I stay with the Delphi RTL and show how modern multithreading concepts can be neatly implemented on that basis. Only at the end I introduce OmniThreadLibrary's concept of a pipeline.
At the end the book admits that sometimes you have to look around and find a prepackaged solution elsewhere. As this solution will be typically compiled for C or C++, the book shows how to link in C object files, how to write a proxy DLL which allows you to use a C++ library and at least tries to introduce you to the world of pain related to all that. Reading this book will definitely not give you enough information on the topic of linking, but at least it will give you a good starting point so that you can research further.
I really hope that you'll like this book. It was a great joy to write, but also lots of very hard work. At the end, all the hard work was immediately forgotten when Stefan Glienke (who very kindly reviewed the whole book and pointed out some glaring errors - Stefan, thanks!) said:
"This is the best Delphi book (for me personally) I've read since 'Delphi in a Nutshell'. It is 'must buy' for our department and mandatory that everyone reads it."
Wednesday, February 28, 2018
Parallel Programming with OmniThreadLibrary - the book is here!
The book covers OmniThreadLibrary version 3.07.5 which was also released today.
The printed book will also be updated, but most probably only with major updates to OmniThreadLibrary. There will not be an update for release 3.07.6 (if there will be such release), but most probably there will be a new version of printed book when OmniThreadLibrary 3.08 is released and there most definitely will be one when version 4.0 comes out.
Here are your options at the moment.
2. To buy the hardcover printed book go to Lulu. For the next month the price is reduced from $49.99 to $45.99 as an introductory offer! I'm still deciding the possibility of also releasing a paperback version but I'm not entirely sure about that as paperback binding on Lulu is reportedly not of high quality. A price of the paperback would be about $10 lower than the price of the hardcover (that is the difference in print costs) and if you think that would make a difference for you, leave me a note.
3. To buy both versions (ebook and printed), go to Lulu and buy the printed book first! You will get an email with a link for ebook at reduced price $9.99 (and combo with webinars for $14.99).
All existing owners of the electronic book should have already received an email with notification about the new release. This email also contains a link to a specially reduced printed book for mere $29.99! If you previously bought the ebook but didn't receive the email, let me know!
Before I sign out for today, let me tell you that writing this book was lots of hard work but also a great joy and I could never do it without all the great people who bought the ebook before it was even completed. Thank you!
OmniThreadLibrary 3.07.5
There are only small number of changes in this release.
General improvements
- Reduced number of times NameThreadForDebugging is called when threadpool is used.
Bug fixes
- [VyPu] fixed race condition in TOmniCriticalSection.Release which affected code that was using TOmniCriticalSection.LockCount.
- OtlThreadPool did not respect OTL_DontSetThreadName define.