The design and implementation of a scalable concurrent virtual machine (Robert Virding)

Robert Virding
Principle Language Expert
at Erlang Solutions Ltd.

Erlang Solutions Ltd.
The Design and Implementation of
a Scalable, Concurrent Virtual
Machine
© 1999-2011 Erlang Solutions Ltd.

Erlang Solutions Ltd.

• The one stop shop for all your Erlang needs
• Founded in 1999, Offices in UK, Sweden and Poland
• Clients on six continents
• System development experience in:
- Telecom, banking, e-commerce, track & trace, VOIP, etc.

• We do:
- In-house system development, on-site consultancy, and
contracting,
- Erlang-based recruitment and Professional training at all
levels

© 1999-2011 Erlang Solutions Ltd. 2

Concurrency vs. Parallelism

• Parallelism is what the system provides
• Concurrency is a property of the problem/
solution

(as good a definition as any)


Erlang is COP

Concurrency Oriented Programming


Problem domain/Erlang properties

• Light-weight concurrency
• Asynchronous message passing
• Process isolation
• Error handling
• Complex coordination
• Soft real-time
• Continuous evolution of system


Erlang is a functional language

• Immutable data
• No looping constructs
• Pattern matching is ubiquitous


The BEAM
The main Erlang implementation
Will cover:
• Processes/scheduling
• Memory management
• Communication
• Error handling
(Bogdan’s Erlang Abstract Machine)


Processes and scheduling

• Want light-weight concurency
• Must have processes (isolation)
➡Implement processes ourselves (green processes)

+ They are really light-weight
+ Complete control of scheduling
- Not a general machine


Processes and scheduling

• One run-queue per thread
• Scheduled as cooperating coroutines
• Multi-core/multi-thread ➡ multi-queues
- Process stealing

• No really viable alternatives


Memory management/GC

• Soft real-time requires unobtrusive GC
• Must ensure process isolation
• Stop-the-world collector
vs.
interactive/concurrent collector
- independent of parallelism


Alternatives:

• Shared heap
• Separate process heaps
• Hybrid
Erlang does NOT require separate
heaps and message copying!


• Shared heap
• Reduces copying of data
• Complicates GC
- must use incremental/concurrent collector

• Less well-suited to multi-core
• Complicates handling of processes



• Separate process heaps
• Increases copying of data
• Simplifies GC
- can use stop-the-world per process collector

• Fits well on multi-core
• Scales well
• Simplifies handling of processes


• Hybrid heaps
• Reduces copying of data
- messages on shared heap

• May in part determined at compile-time
• Complicates GC
• Less well-suited on multi-core
• Erlang BEAM uses very restricted hybrid heaps

Communication - asynchronous
message passing

• Scales well
• Suits multi-core
- needs only limited synchronisation

• Suitable as a building block


Erjang - Erlang on the JVM

• A real Erlang on the JVM
• Will cover:
• Why the JVM?
• How it runs Erlang code
• How it does concurrency
• How it does scheduling
• Memory management/GC
• Miscellaneous © 1999-2011 Erlang Solutions Ltd. 16

Erjang - Why the JVM?

• Wide-spread VM
• Very mature VM
• Improved interface between Erlang and other JVM
languages
• Access to libraries

(Kresten wanted to learn Erlang)


Erjang - Running Erlang code

• Uses BEAM VM assembler code as source to
generate Java
- helps ensure compatibility


Erjang - Concurrency

• Uses Kilim to provide concurrency and message
passing
- ??description??

• Cooperative coroutines
• Asynchronous message passing


Erjang - Scheduling

• One run-queue per thread
• Scheduled as cooperating coroutines
• Multi-core/multi-thread ➡ multi-queues


Erjang - Memory management/GC

• Uses standard JVM memory management/GC
- shared heap
- stop-the-world collector
➡Cannot guarantee soft real-time behaviour (yet)


Erjang - Miscellaneous

• Needs special handling for tail-call optimisation
(a must for functional languages)


• The Erlang User Conference brings together the best minds and names in
Erlang Programming

• This year, the Erlang User Conference will be held in a brand new location
– the exciting, spacious building of the München Bryggeriet.

• An enticing addition to the 2011 conference will be two further tracks.

• We will also be holding a day of tutorials on 4 November.

• In the 3 days prior to the conference, 31 October – 2 November, we will be
holding an Erlang University with a selection of Erlang courses suitable for
all levels of expertise.


Questions?

Thank you

Robert Virding
robert.virding@erlang-solutions.com


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