ITDevCon 2011–recap

ITDevCon 2011 has closed its doors and I’m back at home, completely washed out. It was tiresome but it was also fun!

All the sessions I’ve visited were interesting and I always managed to learn something new. If I would have to expose three most important products I didn’t knew before, I would mention (in the order I learned about them) CopyCat, a great database replication engine which you can compile into your application; Delphi Relax, an extension to Delphi’s WebBroker and DataSnap REST architecture; and DORM, a new ORM for Delphi.

ITDevCon 2011

Just few photos from the opening session …

--- Published under the Creative Commons Attribution 3.0 license

Nasty COM regression in XE2

David Heffernan found a nasty RTL bug in XE2 COM implementation.

Is COM broken in XE2, and how might I work around it?

I’ve found a workaround (see the link above), but it is ugly and this should really be fixed in the next XE2 update so please – vote on the QC #100414!

Update: XE2 Update 2 fixes the bug described above. Great response time from Embarcadero!

 

Multithreading Made Simple–additional material

Thank you for listening to my CodeRage 6 presentation! I’m very sorry that there were some issues with the sound that were caused by network problems :( If you want to look at the presentation again (or for the first time), please go to the Embarcadero CodeCentral or download the presentation from my Dropbox.

To help you understanding the complicated world of multithreading I’ve repacked the complete presentation in a longish PDF with slides and a transcript of my talk. (Actually, it was done vice versa – first I wrote that script and only then I prepared the presentation based on the script.) You can also download the code that was used for the presentation.

If you have any questions or if you asked me something after the presentation and I didn’t understand your question and answered something completely unrelated or even if my answer was too short and you want to learn more - feel free to leave a comment here or open a new topic in the forum.

Multithreading Made Simple

Keep in mind – my session on high-level OmniThreadLibrary stuff goes on air at 06:00 AM PDT / 15:00 CET.

OmniThreadLibrary in Practice [1]–Web Download and Database Storage

From time to time I get a question on the OmniThreadLibrary forum that could be of interest to other OmniThreadLibrary users. As I believe that many of you don’t follow that forum I have decided to repost such questions on the blog (and provide answers, of course).

The first question in this series was asked by GoustiFruit:

I need to download a list of web pages, extract data on them and then store these data in a SQLite database. The downloading/extracting part will happen in multiple threads (I'm using Synapse), but querying the database needs to be done asynchronously as I can only have one concurrent access to it.
So I'd like to know how (conceptually) I could implement that ? My first idea is to run one single thread for querying the DB, run several threads for each Url to download/analyse and then exchange messages between these threads and the querying thread, with the extracted data as a parameter: does it make sense or am I totally wrong? I also read things about the connection pool concept but I'm not sure if it applies when only one connection is allowed at one time?

CodeRage 6 is Starting!

Tomorrow starts the CodeRage week!

My presentation is scheduled for Friday, 21st, at 06:00 PDT / 15:00 CET, which is early for the West coast folks but great for East cost and us Europeans. See you there!

OmniThreadLibrary 2.2

Only three months since 2.1 and a new release is already here? What’s going on?

I had to change some things to make OTL work in XE2 and although I could simply release new files as a patch I noticed that I’ve also done quite some work on exception handling and that I could equally well wrap everything in a new release.

Here it is: ZIP, SVN, UML diagrams (provided by Rich Shealer; Rich, thanks!).

Hear Me at CodeRage

CodeRage 6 will start in ten days! Will you be there? I’ll be joining it for the sixth time as a listener and for the first time as presenter!
The exact date and time of the presentation was not determined yet (if you look at the session list you’ll see some empty spots – I’m one of them). I’ll let you know when the timeslot is fixed. In the meantime, go and register for the conference!
The topic of my talk you can probably guess – multithreading with the OmniThreadLibrary. Due to a limited session time and to attract as wide an audience as possible, I’ve decided to focus on high-level OTL functionality. The title of the talk is Multithreading made simple and it will deal with Async, Future, ForEach, Pipeline, ForkJoin, Join, and ParallelTask.

NeverSleepOnThreadContention–NOT!

FastMM is a wonderful memory manager, but it can slow down quite a lot when used in multithreading environment. While Pierre has implemented some conditional defines that could help the multithreaded code, namely NeverSleepOnThreadContention and SwitchToThread, I’m now making a point that you shouldn’t ever use them! Just see for yourself.

Meet Me in Verona

I know that XE2 on Win64, OS/X and iOS is all the rage but some of us (or is it most of us?) still have to make living in the Win32 world. That’s why my ITDevCon 2011 talks are not focused into specific technologies but into techniques and tools that will make your life easier. (At least your life as a programmer, that is.)

If you have time and you live close enough, come to Verona at the end of October and meet many interesting people. Lots of speakers, three separate tracks, free lunch and wifi – what do you want more? David I is rumored to be there, Marco Cantù will lead sessions all the time and you’ll have a chance to talk to me. I’ll be giving four sessions, some targeted at beginners, some at experienced programmers. (All between those extremes are also invited, of course.)

Life after 2.1: Parallel data production [Introducing Parallel.Task]

An interesting problem appeared on StackOverflow shortly ago – how to generate large quantities of data as fast as possible and store it in a file. (As one could expect) I wrote a parallel solution using OmniThreadLibrary, more specifically the Parallel.ForEach high-level primitive. I’m not posting the complete solution here, just the important part – a method that accepts two parameters, requested file size and output stream, and generates the data. Actual initialization of data buffers is delegated to the FillBuffer method which you can see in the StackOverflow post.

Life after 2.1: Pimp My Pipeline

While the biggest focus on the Pipeline improvement was on the exception handling, there were also some changes in the basic functionality.

The most important (and code breaking!) change happened to the Input function, which was renamed to From. If you now want to pass a input queue to a pipeline, use pipeline.From(queue).

Second code breaking change happened to the Run function which now returns IOmniPipeline (i.e. the pipeline interface) itself, not the output blocking collection. Luckily, both changes will be caught by the compiler which would not want to compile the old code any more.

Multithreading is Hard!

I have known for a long time that there’s a potential race condition between two writers in TOmniBlockingCollection but I thought that it doesn’t present and clear and present danger. Boy was I wrong!

Life after 2.1: Parallel.Join’s new clothes

Parallel.Join has started its life as a very simple construct.

class procedure Join(const task1, task2: TProc); overload;
class procedure Join(const task1, task2: TOmniTaskDelegate); overload;
class procedure Join(const tasks: array of TProc); overload;
class procedure Join(const tasks: array of TOmniTaskDelegate); overload;

Later it got an optional parameter of the IOmnITaskConfig type, but that didn’t change its simplicity. You called Join, it executed some code in parallel, and only when all code blocks completed its execution, your main thread would proceed by executing the statement following the Join call.
Then I started to think about handling exceptions (just as I did for the Parallel.Future) and somehow this simplicity didn’t feel right to me anymore. At the same time I got involved in a prolonged discussion with Антон Алисов (Anton Alisov) and together we defined new features that new Join would have to have.

OmniThreadLibrary 2.1 hotfix

All users of the 2.1 release, please download this very important hotfix.

There was a nasty bug in OtlEventMonitor where FreeAndNil was called on a variable containing garbage from the stack. >:-(

Great thanks to [Антон Алисов] for finding the problem.

Life after 2.1: Exceptions in Parallel.Future

The main focus in the next OmniThreadLibrary release is on exception handling in high-level constructs (i.e. the OtlParallel unit). The first one to get this support is Parallel.Future. Why? Simple reason – it has a well-defined point of interaction with the owner (the Value function) and only one background task, which makes exception handling easy to implement.
IOmniFuture<T> was extended with three functions.

  IOmniFuture<T> = interface
    procedure Cancel;
    function  DetachException: Exception;
    function  FatalException: Exception;
    function  IsCancelled: boolean;
    function  IsDone: boolean;
    function  TryValue(timeout_ms: cardinal; var value: T): boolean;
    function  Value: T;
    function  WaitFor(timeout_ms: cardinal): boolean;
  end; { IOmniFuture<T> }

Any exception thrown in the background task and not caught in the future-calculating code will be caught by the IOmniFuture<T> implementation. When a Value is accessed, this exception will be raised in the owner thread.

Life after 2.1: Async redux

OtlParallel unit defines four overloaded Async methods in OTL v2.1:

class procedure Async(task: TProc; taskConfig: IOmniTaskConfig = nil); overload;
class procedure Async(task: TOmniTaskDelegate; 
  taskConfig: IOmniTaskConfig = nil); overload;
class procedure Async(task: TProc; onTermination: TProc; 
  taskConfig: IOmniTaskConfig = nil); overload;
class procedure Async(task: TOmniTaskDelegate; onTermination: TProc;
  taskConfig: IOmniTaskConfig = nil); overload;

As it turned out, two of them are not necessary anymore. Since the introduction of the taskConfig parameter, termination procedure can also be specified by setting taskConfig.OnTerminated.

OmniThreadLibrary 2.1

Yes, it is ready. Get the ZIP or check it from SVN.

If you’re following the trunk, do the update. You’ll actually get more than 2.1 as I’ve already merged in development branch with support for exception handling in Parallel.Future and Parallel.Join. Warning – those changes may break the code as two version of Parallel.Async were removed. Check the history.txt and documentation in OtlParallel.pas for more info.

This time you can also download full UML diagrams for OmniThreadLibrary, courtesy of Rich Shealer.

2.1 release should be mostly non-breaking, except for changes in OtlHook exception filtering mechanism and removed EXIT_EXCEPTION exit code (see below for more info).

I’d like to thank dottor_jeckill, Rico Krasowski, vcldeveloper and TOndrej, who helped make this release even more awesomer.

Getting ready for OmniThreadLibrary 2.1

After a long long wait (sorry folks, due to events out of my control this release took many months longer that I expected) OmniThreadLibrary 2.1 is finally ready!

I’m just putting together change log, testing demos to see if everything is working as it should and so on … A day or two and it will be packed and ready to go. If you’re impatient, just go ahead and check out the current version from the SVN – all the code is already in there.

I have a small favor to ask, though. If you’re using OmniThreadLibrary in D2009 or D2010 – can you please make sure that all tests are included in the appropriate Tests.<version>.groupproj file (and create missing <project name>.<version>.dproj files in the process)? And send the changes to me, of course – my email address is in OTL source files. It would be best if you can leave a comment here if you choose to help me so that the work won’t be duplicated by other programmers.

Thanks in advance, that will really help me getting OTL out quickly. (Otherwise I have to set up a virtual machine and install D2009 and D2010 as I’m not using them for everyday work anymore.)

EDIT: D2010 projects and updated test group are now in the repository, thanks to [vcldeveloper].

EDIT: D2009 projects and updated test group are now in the repository, thanks to [TOndrej].