Simple Concurrent Object-oriented Programming

Simple Concurrent Object-Oriented Programming Nati Fuks

Department of Computer Science, York University

SCOOP Outline  SCOOP Introduction  Generator  SCOOP vs Java  PRODUCER-CONSUMER example  SCOOP Semantics  Mapping from SCOOP to Eiffel+THREADs

Department of Computer Science, York University

Concurrency  Concurrent programming is difficult  e.g. Java Memory Flaw circa 1999  A variety of mechanisms must be mastered  Thread class, synchronize, wait, notify, mutexes, monitor, critical regions  Problems such as deadlock, safety and liveness properties, inheritance anomaly

Department of Computer Science, York University

SCOOP A single new keyword (separate) provides for a fullfledged concurrency mechanism !!!

SCOOP platform-independent

Eiffel + Threads

.NET Framework

Department of Computer Science, York University

POSIX

…

SCOOP SCOOP: Simple Concurrent Object-Oriented Programming. Defined by Bertrand Meyer in OOSC in 1997 Implementations: 1. Compton. Changes in the open source SmallEiffel compiler 2. This work 3. SCOOP in the .NET framework

Department of Computer Science, York University

SCOOP Generator Why SCOOP Generator? Object-Oriented Design Design By Contract Simple and intuitive concurrency model of SCOOP

What do we achieve? Concurrent programs using SCOOP

Department of Computer Science, York University

SCOOP Generator 

Eiffel SCOOP -> Eiffel + THREAD

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Standard Eiffel code (mutexes and THREADs)

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Eiffel Studio 5.4 Advantages 

Pure Eiffel

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Independence

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Target code is cross-platform

Disadvantage – Debugging on a target code Department of Computer Science, York University

Producer-Consumer Java Solution

Department of Computer Science, York University

Producer-Consumer SCOOP Solution

- same behaviour as the Java solution - only one extra keyword separate is used (||) - uses contracts with all the benefits of DbC

Department of Computer Science, York University

ROOT_CLASS class ROOT_CLASS creation make feature b: separate BUFFER p: PRODUCER -- declared separate c: CONSUMER -- declared separate make is do

end

end

-- Creation procedure. create b.make create p.make(b) create c.make(b)

Department of Computer Science, York University

Bounded BUFFER class BUFFER creation make feature put (x:INTEGER) is require count <= 3 do q.put(x) ensure count = old count + 1 and q.has (x) end remove is require count > 0 do q.remove ensure count = old count - 1 end … Department of Computer Science, York University

PRODUCER separate class PRODUCER creation make feature buffer: separate BUFFER make (b: separate BUFFER) is do …keep_producing … end keep_producing is do … produce(buffer,i) … end produce (b : separate BUFFER; i:INTEGER) is require b.count <= 2 do b.put(i) ensure b.has(i) end end

Department of Computer Science, York University

CONSUMER separate class CONSUMER creation make feature buffer: separate BUFFER make (b: separate BUFFER) is do …keep_consuming… end keep_consuming is do …consume(buffer)… end consume (b: separate BUFFER) is require b.count > 0 do b.remove ensure b.count = old b.count - 1 end end Department of Computer Science, York University

Synchronization in SCOOP A call to the routine produce with a separate will block until:

(a) the producer gets sole access to the buffer

+ (b) the buffer must not be full as indicated in the precondition

Department of Computer Science, York University

Preconditions in SCOOP if not buffer.full then buffer.put(value) produce (b: separate BUFFER; i: INTEGER) is require b.count <= 2 i >= 0 do b.put (i) end

Department of Computer Science, York University

Mapping to Eiffel + THREAD separate class ROOT_CLASS

feature

class ROOT_CLASS inherit THREAD_CONTROL feature request_pended: INTEGER_REF requests_pended_mutex:MUTEX

b:separate BUFFER b:BUFFER b_mutex: MUTEX p:PRODUCER p:PRODUCER

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Mapping to Eiffel 2 make is do

create b.make

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make is do requests_pended := 1

b_mutex.lock create b.make b_mutex.unlock

Mapping to Eiffel 3 create p.make (b) create p.make (b, b_mutex, requests_pended, requests_pended_mutex) p.launch set_feature_to_do ([Current, "KEEP_PRODUCING_ROUTINE"])

Department of Computer Science, York University

Mapping to Eiffel 4 create c.make (b)

same as p.make…

requests_pended_mutex.lock requests_pended.copy (requests_pended-1) requests_pended_mutex.unlock

end Department of Computer Science, York University

join_all end

Contributions  Analysis of Meyer’s SCOOP with a view to implementation – semantics of SCOOP via Compton’s subsystems  Based on the semantics of SCOOP – provided a mapping from SCOOP to Eiffel + Threads.  Generator parses SCOOP programs, flags syntax errors and automatically translates to portable executable code based on the mapping.  First full implementation of SCOOP  contracts  routine calls with multiple separate objects

Department of Computer Science, York University

Thank You

Department of Computer Science, York University