Presented on July 14, 2013 at the annual KDE Akademy conference: ThreadWeaver is the concurrency scheduler framework in KDE. It provides a high-level multi-threading API convenient for application programming, combined with powerful features like aggregate tasks, task dependencies and queue policies. With the dawn of KDE Frameworks, ThreadWeaver has been refactored, extensively tested, benchmarked and generally polished. This presentation will introduce the audience to ThreadWeaver programming and central concepts, explain the (few) changes and additions in the API in KDE Frameworks, and show some performance benchmarking results.

1. ThreadWeaver in KDE
Frameworks 5
Demos, New Features, Performance
Mirko Boehm <mirko@kde.org>
Akademy 2013
1Friday, July 19, 13

2. Agenda
introduction to ThreadWeaver
key concepts: job aggregates, policies, queues
API changes for Frameworks 5
performance considerations, benchmarks
outlook and new feature quizz
2Friday, July 19, 13

3. CWD: ~
miroslav@silberpfeil: >whoami
- KDE Contributor since 1997:
-- hacking (kdecore, kdepim, applications)
-- board member 1999 to 2006
-- Desktop Summit 2011
- FSFE Team Germany
- researching Free Software and Intellectual Property
issues at TU Berlin
- European Representative, Open Invention Network
- Founder/CEO,Endocode AG
- married, two kids, lives in Berlin
CWD: ~
miroslav@silberpfeil: >
3Friday, July 19, 13

4. Agenda
introduction to ThreadWeaver
key concepts: job aggregates, policies, queues
API changes for Frameworks 5
performance considerations, benchmarks
outlook and new feature quizz
4Friday, July 19, 13

5. Hello World
Demo time!
5Friday, July 19, 13

6. Hello World demo(s)
global ThreadWeaver pool
job memory management
shared pointers
raw pointers, jobs as stack variables
Lambda jobs
6Friday, July 19, 13

7. Sequence
Demo
Demo time!
7Friday, July 19, 13

8. Sequence Demo
job aggregates: collections, sequences
job error reporting
sequences abort on failure
signals and slots to communicate
sharing data between jobs
8Friday, July 19, 13

9. Image
Viewer
Demo time!
9Friday, July 19, 13

10. Image Viewer
queue policies
resource restrictions
dependencies
job priorities
worker thread count, individual queue instances
10Friday, July 19, 13

11. Outlook
Use job aggregates
to model execution
flow graph.
(Or: How to draw a
sad robot.)
11Friday, July 19, 13

12. Agenda
introduction to ThreadWeaver
key concepts: job aggregates, policies, queues
API changes for Frameworks 5
performance considerations, benchmarks
outlook and new feature quizz
12Friday, July 19, 13

13. Jobs
units of queueing and execution
shared pointers for memory management
raw pointers for stack variables
success status,
cancellation requests
priorities as a hint to the scheduler
13Friday, July 19, 13

14. Queue Policies
decide whether or not a job can be executed
are assigned to jobs
may be shared between jobs or queues
built-ins:
resource restriction policy, dependency policy
custom policies can be implemented
14Friday, July 19, 13

15. Queues
manage worker threads
global instance or individual instances
suspend/resume/finish
signaling
15Friday, July 19, 13

16. Philosophy
scheduling vs. programmed concurrency
critical path modeling
minimalism (jobs, queueing methods, concepts)
simplicity
16Friday, July 19, 13

17. Agenda
introduction to ThreadWeaver
key concepts: job aggregates, policies, queues
API changes for Frameworks 5
performance considerations, benchmarks
outlook and new feature quizz
17Friday, July 19, 13

18. API changes
few, but important
shared pointers for jobs
global instance child of QApplication
public Queue class
ExecuteWrapper
all *RunHelper* classes removed
18Friday, July 19, 13

19. Agenda
introduction to ThreadWeaver
key concepts: job aggregates, policies, queues
API changes for Frameworks 5
performance considerations, benchmarks
outlook and new feature quizz
19Friday, July 19, 13

20. 20Friday, July 19, 13

21. Agenda
introduction to ThreadWeaver
key concepts: job aggregates, policies, queues
API changes for Frameworks 5
performance considerations, benchmarks
outlook and new feature quizz
21Friday, July 19, 13

22. Feature quizz
progress tracking
minijobs
embed QRunnables
Job::execUntilFinished(QEventLoop/QDialog/qApp)
AnyOfCollection
UI elements/visualizations
22Friday, July 19, 13

23. Questions?
23Friday, July 19, 13

24. References
demos:
github.com/mirkoboehm/ThreadWeaverDemos
benchmarks:
github.com/mirkoboehm/QBenchmarkParser
code:
kdelibs frameworks branch, tier1/threadweaver
24Friday, July 19, 13