Saturday, April 28, 2018

Another Bug

So you've put in the time and effort to refactor your code and data for parallel execution and are eager to see some parallel action. Unfortunately, you might be disappointed; in some cases your tasks might get serialized, performed sequentially in a single thread. With the overhead you've just introduced, your code probably performs a little bit worse than before.

If you thought TParallel.Join was a nasty bug, things can apparently get even worse. Reading further in Primož Gabrijelčič's book Delphi High Performance, Chapter 7, "Exploring Parallel Practices":

There's a nasty bug in the System.Threading code that was introduced in Delphi 10.2 Tokyo. I certainly hope that it will be fixed in the next release, as it makes the Parallel Programming Library hard to use. It sometimes causes new threads not to be created when you start a task. That forces your tasks to execute one by one, not in parallel.

(Interestingly, I'm able to reproduce it reliably in XE7, too.)

The ParallelTasks sample project demonstrates the issue.
If you run the "Check primes 2" code with four tasks first, then two tasks, and finally one task, you'll get the expected result:

However, running the code with one task first, then two tasks, and finally four tasks will give you this:

The author offers two different workarounds:
- insert a little delay after each call to TTask.Run (in the sample code, uncomment the Sleep(1) call in btnCheckPrimes2Click method), or
- create your own thread pool and limit the minimum number of running threads in it (in the sample code, see btnCustomThreadPoolClick method).

Sunday, April 22, 2018

Don't lose time with a known Delphi bug affecting TParallel.Join

Writing multi-threaded code is hard and takes a lot of time. That's why it's especially annoying to waste time with bugs like this.

Reading (and enjoying) Primož Gabrijelčič's book Delphi High Performance, I've come across this paragraph in Chapter 7: Exploring Parallel Practices:
There's not much to say about Join, except that in current Delphi it doesn't work correctly. A bug in the 10.1 Berlin and 10.2 Tokyo implementations causes Join to not start enough threads. For example, if you pass in two tasks, it will only create one thread and execute tasks one after another. If you pass in three tasks, it will create two threads and execute two tasks in one and one in another.
The code accompanying the book is available on Github: PacktPublishing/Delphi-High-Performance

G+ discussion
TParallel,Join does not create enough threads (Embarcadero's Quality Portal RSP-19557)

The author offers a simple workaround by starting a dummy task (which does nothing) first; you can see an example here.

Some time ago (using Delphi XE7), I wrote a library with my own TThreadPool class using and encapsulating the Windows IOCP. The result turned out well, it was rock-solid. Reading about bugs like this in the latest-and-greatest Delphi version makes me glad I chose to write my own implementation from scratch and saved a lot of time hunting for bugs like this in Delphi's runtime library (in addition to my own).

Sunday, April 15, 2018

Artificial Intelligence Transgender: Kings and Queens

Researching for some Natural Language Processing tasks for a .NET application recently, I've come across Facebook's FastText library.

FastText is an open-source, free, lightweight library that allows users to learn text representations and text classifiers. It works on standard, generic hardware. Models can later be reduced in size to even fit on mobile devices.
It's written in C++ and builds on modern Mac OS and Linux distributions. Since it uses some C++11 features, it requires a compiler with good C++11 support. Python bindings are included.

Using this library, you can train models which represent words as multi-dimensional vectors. The models can be queried to find correlations between these vectors in the multi-dimensional space. Depending on the volume and quality of your input data, as well as the training parameters you specify, you can obtain better or worse results to your queries. An introductory explanation of how it works: king - man + woman is queen; but why?

An unofficial FastText fork for Windows is available on GitHub. I'm using this as a starting point to create a DLL in Visual Studio, exposing the C++ classes in a "flattened" C-style API as described in the article Using C++ objects in Delphi by Rudy Velthuis. Such a DLL can also be used from .NET via platform invoke.

As a result, when it's done I'll be able to use this library from Python, .NET, Delphi/Free Pascal and JavaScript (by embedding ChakraCore).

Some examples of console output from my experiments:

King - Man + Woman = ? (JavaScript)

C:\Code\fasttextConsole\chakra\Win64\Debug>ftcc ft.js
Loading file "C:\Data\fasttext\wiki\enwik9.bin"...
Computing vectors...
positive words:
king woman
negative words:
"queen": 0.7796817421913147
"regnant": 0.7554017305374145
"consort": 0.7433754205703735
"daughter": 0.7231032848358154
"throne": 0.721994161605835

Berlin - Germany + Argentina = ? (C#)

Loading file "C:\Data\fasttext\wiki\enwik9.bin"...done.
Computing vectors...done.
positive words:
berlin argentina
negative words:
"aires": 0.8183396
"buenos": 0.8142648
"argentinan": 0.7616609
"argentinas": 0.7580159
"caracas": 0.740073

Berlin - Germany + Slovakia = ? (Free Pascal)

Loading file 'C:\Data\fasttext\wiki\enwik9.bin'...done.
Computing vectors...done.
positive words:
berlin slovakia
negative words:
'zagreb': 0.81 (Oops! ;-))
'bratislava': 0.79 (Yeah!)
'budapesti': 0.79
'slavonski': 0.79
'podgorica': 0.78

Playstation - Sony + Nintendo = ? (JavaScript)

C:\Code\fasttextConsole\chakra\Win64\Debug>ftcc ft.js
Loading file "C:\Data\fasttext\wiki\enwik9.bin"...
Computing vectors...
positive words:
playstation nintendo
negative words:
"gamecube": 0.8729094862937927
"nintendogs": 0.8490696549415588
"playstationjapan": 0.840140163898468
"snes": 0.8312469720840454
"sega": 0.822517454624176

Here are some code examples:

1. C-style API (DLL exported functions)
2. Imports for .NET
3. Wrapper class for .NET
4. C# usage
5. Imports for Pascal
6. Pascal usage
7. Pascal class for ChakraCore host
8. JavaScript usage

Monday, April 02, 2018

First steps with Lazarus Qt5 interface

Steps for building and installing Qt5 for Lazarus

Using a quick test project with relevant code shown here: unit1.pas
I'm using Qt 5.6.2 because that's the version with which Lazarus qt5 interface has been tested. You can experiment with later versions, too.

Windows 32-bit

Using MinGW

$(LazarusDir): C:\fpcupdeluxe\lazarus
$(QtDir): C:\Qt\Qt5.6.2

- download: qt-opensource-windows-x86-mingw492-5.6.2.exe
- install
- open command prompt in the bindings directory $(LazarusDir)\lcl\interfaces\qt5\cbindings
set PATH=$(QtDir)\5.6\mingw49_32\bin;$(QtDir)\Tools\mingw492_32\bin;%PATH%
mingw32-make install
$(FpcDir)\bin\i386-win32\strip.exe $(QtDir)\5.6\mingw49_32\bin\Qt5Pas1.dll

Windows 64-bit

Using Visual Studio 2015

$(LazarusDir): C:\fpcupdeluxe\lazarus
$(QtDir): C:\Qt\Qt5.6.2

- download: qt-opensource-windows-x86-msvc2015_64-5.6.2.exe
- install
- fix the binding sources in the bindings directory $(LazarusDir)\lcl\interfaces\qt5\cbindings to be able to compile with Visual Studio: patch
- open command prompt in the bindings directory $(LazarusDir)\lcl\interfaces\qt5\cbindings
set PATH=$(QtDir)\5.6\msvc2015_64\bin;%PATH%
"C:\Program Files (x86)\Microsoft Visual Studio 14.0\VC\vcvarsall.bat" amd64

- edit the Makefile to remove -Wfatal-errors from CXXFLAGS
nmake install

OSX 64-bit

$(LazarusDir): ~/fpcupdeluxe/lazarus
$(QtDir): ~/Qt5.6.2

- download: qt-opensource-mac-x64-clang-5.6.2.dmg
- install
- open terminal in the bindings directory $(LazarusDir)/lcl/interfaces/qt5/cbindings
sudo make install

Linux 64-bit (Mint 18.3 Sylvia)

$(LazarusDir): ~/fpcupdeluxe/lazarus
$(QtDir): ~/Qt5.6.2

- make sure OpenGL headers are installed:
sudo apt install mesa-common-dev
sudo ln -s /usr/lib/x86_64-linux-gnu/mesa/ /usr/lib/
sudo ldconfig

- download:
- install
Modify the system-wide config in /usr/lib/x86_64-linux-gnu/qt-default/qtchooser/default.conf to point to your Qt5 directories:

- open terminal in the bindings directory $(LazarusDir)/lcl/interfaces/qt5/cbindings
sudo make install
sudo strip $(QtDir)/5.6/gcc_64/lib/

Happy Easter!