SCOOP: Simple Concurrent Object-Oriented Programming

1
SCOOP Simple Concurrent Object-Oriented
Programming

• Piotr Nienaltowski, Volkan Arslan, Bertrand Meyer
• presented by Mark Schall

2
The Problem

• What is the simplest, smallest and most
  convincing extension to the method of systematic
  object-oriented software construction that can
  address the needs of concurrent and distributed
  computing as well as those of sequential
  computation? Bertrand Meyer

3
SCOOP Model

• High-level concurrency mechanism
• Based on Design by Contract
• Full use of inheritance
• Applicable to many physical setups
  multiprocessing, multithreading, distributed
  execution

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Brief History

• First published in 1993 by Bertrand Meyer
• Designed as extension to Eiffel
• First prototype was implemented in 1995

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Architecture

• Top Layer
• platform independent
• Bottom Layer
• language/platform specific

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Bottom Layer

• Eiffel
• Added single new keyword separate
• .NET
• Add two new classes to be inherited
• SEPARATE_CLIENT
• SEPARATE_SUPPLIER

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Separate Calls

• Keyword separate declares if an object should be
  handled on the same processor or not

• SOME_ROUTINE( x separate CLASS ) is
• do
• x.f()
• end
• x separate CLASS
• create x.make
• b.SOME_ROUTINE(x)

x.f() will be handled on a different processor
then the call b.SOME_ROUTINE(x)
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Client and Supplier
Object b (Client) Processor 1
Object x (Supplier) Processor 2
SOME_ROUTINE(x) x.f()
f() is do end
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Processors

• Not just mean physical CPU
• Threads
• Processes
• Computers in a distributed system
• Application Domain

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Access control policy

• Separate calls are valid if the target of the
  call is an argument of the enclosing routine
• SOME_ROUTINE( x separate CLASS ) is
• do
• x.f()
• end
• a separate CLASS
• create a.make
• SOME_ROUTINE(a) -- instead of a.f()

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Basic Access Control Policy Example

• Processor 1
• while( !lock(a) )
• wait( a )
• SOME_ROUTINE(a)
• a.f()
• release(a)

Processor 2 f() is do end
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Access control policy

• Using Design by Contract
• store(buffer separate BUFFER value INTEGER) is
• require -- precondition
• buffer_not_full not buffer.is_full
• do
• buffer.put(value)
• ensure -- postcondition
• buffer_not_empty not buffer.is_empty
• end
• buf separate BUFFER
• store(buf, 20)

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Wait by necessity

• Client Objects
• do not need to wait for feature calls of a
  supplier in order to call another feature call
• must wait on query calls for all previous calls
  to finish on the same supplier

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Example

• some_feature( x, y, z separate CLASS ) is
• do
• x.f
• y.f
• x.g
• z.f
• y.g
• v x.is_empty -- wait for x.f and x.g
• v x.value gt y.value -- wait for y.f and y.g
• end

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Producer/Consumer Example

• ProduceAndConsume( p separate PRODUCER, c
  separate CONSUMER ) is
• do
• c.consume_n(5)
• p.produce_n(5)
• end
• buf separate BUFFER
• consumer separate CONSUMER
• producer separate PRODUCER
• create c.make(buf)
• create p.make(buf)
• ProduceAndConsume(producer, consumer)

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Producer
store (buffer separate BUFFER INTEGER value
INTEGER) is require buffer_not_full not
buffer.is_full value_provided value /
Void do buffer.put (value) end

• produce_n (n INTEGER) is
• local
• value INTEGER
• i INTEGER
• do
• from i 1
• until i gt n
• loop
• value random_gen.next
• store (buf, value)
• i i 1
• end
• end
• end -- class PRODUCER

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Consumer

• consume_n (n INTEGER) is
• local
• i INTEGER
• do
• from i 1
• until i gt n
• loop
• consume_one (buf)
• i i 1
• end
• end

consume_one (buffer separate BUFFER INTEGER)
is require buffer_specified buffer /
Void buffer_not_empty not buffer.is_empty do valu
e buffer.item buffer.remove end
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Producer/Consumer Example

• ProduceAndConsume( p separate PRODUCER, c
  separate CONSUMER ) is
• do
• c.consume_n(5)
• p.produce_n(5)
• end
• buf separate BUFFER
• consumer separate CONSUMER
• producer separate PRODUCER
• create c.make(buf)
• create p.make(buf)
• ProduceAndConsume(producer, consumer)

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Reusing old software

• Support for inheritance allows for reuse of
  non-concurrent software
• May only require a simple wrapper class
• separate class BUFFER
• inherit QUEUE
• end

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Distributed Computing

• Processors can be Computers in the network
• Concurrency Control File
• maps processors to physical addresses
• machines
• processes
• etc.
• Can take advantage of .NET Remoting library

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Distributed Computing
Internet
Home Desktop
arctic.cse.msu.edu
LAN
pacific.cse.msu.edu
Processor 1
Processor 4
Processor 3
o5
o1
o3
Processor 5
Processor 2
o4
o6
o2
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Duels

• An attempt to grab a shared object from the
  current holder
• Holder
• retain (default)
• yield
• Challenger
• wait_turn (default)
• demand
• insist
• Exceptions interrupt either the Holder or
  Challenger to settle the Duel

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Future Work

• Real-time programming
• Priority mechanisms
• Timeout controls
• Deadlock Avoidance

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Future Work

• RECOOP Reliable and Efficient Concurrent
  Object-Oriented Programs
• Microsofts Safe and Scalable Multicore Computing
  RFP
• Continuation of SCOOP
• Developing a practical formal semantics and proof
  mechanism