1. Multithreading Made Simple with OmniThreadLibrary
Primož Gabrijelčič

2. Introduction

3. OmniThreadLibrary is …
… VCL for multithreading
Simplifies programming tasks
Componentizes solutions
Allows access to the bare metal
… trying to make multithreading possible for mere mortals
… providing well-tested components packed in reusable classes with high-level parallel programming support
… parallel programming today!
“Why multithreading?” is most probably not a question anymore
“Why not TThread?” is harder to answer - maybe a good answer would be “Because not CreateWindow”

4. Delphi 2007 and above; currently Win32 only
Project status
OpenBSD license
Actively developed
1008 commits
Actively used
2.0: 2710 downloads [in 7 months]
2.1: 1187 downloads [in 3 months]
2.2: current release, XE2 support
Delphi 2007 and above; currently Win32 only

5. Add the OtlParallel unit to the uses list That’s all folks!
Installation
Download last installation from the Google Code or checkout the SVN repository
code.google.com/p/omnithreadlibrary/
Add installation folder and its src subfolder to the project search path or Win32 library path
Add the OtlParallel unit to the uses list
That’s all folks!

6. Future
Win64
FMX
OS/X
iOS?

7. OmniThreadLibrary basics

8. Task vs. thread Task is part of code that has to be executed
Thread is the execution environment
You take care of the task, OTL takes care of the thread

9. Communication TOmniValue = variant
T/IOmniBlockingCollection = threadsafe queue with read-blocking behaviour
Message/data passing can solve most synchronisation problems (shared data access, deadlocking)

10. High-level multithreading

11. Be afraid
“New programmers are drawn to multithreading like moths to flame, with similar results.”
-Danny Thorpe

12. Why high-level approach?
Designing parallel solutions is hard
Writing multithreaded code is hard
Testing multicore applications is hard
Debugging multithreading code is pure insanity
Debugging multithreading code is hard
Cross out off of this stuff – high-level primitives help you exactly with that

13. High-level multithreading
Async
start background task and continue
Future
start background calculation and retrieve the result
Join
start multiple background tasks and wait
ParallelTask
start multiple copies of one task and wait

14. High-level multithreading
ForEach
parallel iteration over many different containers
Pipeline
run a multistage process
Fork/Join
divide and conquer, in parallel
Delphi 2009 required

15. Parallel.Async(code) Async Demo (probably HttpGet): async
get and ignore result
async with communication
task.comm.send …
async with invoke
explain that this is better handled with Future

16. Future:=Parallel.Future<type>. (calculation);
Query Future.Value;
future httpget
add termination handler
show exception handling

17. Parallel.Join([task1, task2, task3, … taskN]).Execute
Use Join to get three different pages with HttpGet
explain exception handling

18. Parallel.ParallelTask.Execute (code)
need a better demo

19. ParallelFor
Parallel.ForEach(from, to).Execute( procedure (const value: integer); begin //… end)
Parallel.ForEach(source).Execute( procedure (const value: TOmniValue); begin //… end)

20. ParallelFor
Demo simple parallel for; nowait variant; ordered variant; maybe even aggregates
Demo enumeration over different sources

21. Pipeline example Pipeline example:
Simple read-compress-encrypt-write process
For each doesn’t help here, both in compression and encryption process (may) depend on previously processed data
What does R-C-E-W process really do? It consists of four parts, each processing data.
Usually we don’t process complete data in each part before continuing into next.
We can rewrite this code to use queues instead of fixed buffers. Why? …
… Because now we can split those four parts into four threads.
Threads execute overlapped.
Total execution time (providing multicore machine) if much shorter.

22. Parallel.Pipeline([stage1, stage2, stage3]). Run
“encryption” demo should work fine
demo throttling
explain exception handling

23. Fork/Join
Divide and conquer
QuickSort demo

24. Multithreading is hard?

25. Why high-level approach?
Designing parallel solutions is hard
Writing multithreaded code is hard
Testing multicore applications is hard
Debugging multithreading code is pure insanity
Debugging multithreading code is hard
Cross out off of this stuff – high-level primitives help you exactly with that

26. Questions?