Chair of Software Engineering PPoPP 2003, , San Diego SCOOP it up! Piotr Nienaltowski Chair of Software Engineering, ETH Zurich, Switzerland joint work with Volkan Arslan and Bertrand Meyer ETH Zurich

Chair of Software Engineering PPoPP 2003, , San Diego Motivation  Extend a pure, strongly typed, object-oriented language (Eiffel, …) with a simple, general and powerful concurrency model  Provide the IT industry with a simple and powerful model for parallel programming  Make programmers sleep better!  Let them forget about all the nightmares of parallel programming and make their lives easier

Chair of Software Engineering PPoPP 2003, , San Diego The SCOOP model  Simple Concurrent Object-Oriented Programming  High-level concurrency mechanism  Full use of inheritance and other object-oriented techniques  Applicable to many physical setups: multiprocessing, multithreading, distributed execution, etc.  Based on Design by Contract

Chair of Software Engineering PPoPP 2003, , San Diego Object-oriented computation To perform a computation is  to use certain processors  to apply certain actions  to certain objects.

Chair of Software Engineering PPoPP 2003, , San Diego What makes an application concurrent? Processor: autonomous thread of control supporting sequential execution of instructions on one or more objects Can be implemented as:  CPU  Process  Thread  AppDomain (.NET) …

Chair of Software Engineering PPoPP 2003, , San Diego Feature call (synchronous)  Fundamental scheme of O-O computation: feature call x.f (a)  x: CLASS_X

Chair of Software Engineering PPoPP 2003, , San Diego Separate feature call (asynchronous)  Fundamental scheme of O-O computation: feature call x.f (a)  x: separate CLASS_X

Chair of Software Engineering PPoPP 2003, , San Diego Access control policy  Target of a separate call must be a formal argument of the enclosing routine: store (buffer: separate BUFFER; value: INTEGER) is -- Store value into buffer. do buffer.put (value) end  To obtain exclusive access to a separate object, use it as argument of the call: store (my_buffer, 10)

Chair of Software Engineering PPoPP 2003, , San Diego From preconditions to wait-conditions Contracts in Eiffel store (buffer: BUFFER; value: INTEGER) is -- Store value into buffer. require not buffer.is_full value > 0 do buffer.put (value) ensure not buffer.is_empty end... store (my_buffer, 10)  If b is separate, precondition becomes wait condition (instead of correctness condition)

Chair of Software Engineering PPoPP 2003, , San Diego From preconditions to wait-conditions Contracts in Eiffel store (buffer: separate BUFFER; value: INTEGER) is -- Store value into buffer. require not buffer.is_full value > 0 do buffer.put (value) ensure not buffer.is_empty end... store (my_buffer, 10)  If buffer is separate, precondition becomes wait condition.

Chair of Software Engineering PPoPP 2003, , San Diego Synchronization  No special mechanism needed for client to resynchronize with supplier after separate call.  The client will wait only when it needs to: x.f x.g (a) y.f … value := x.some_query

Chair of Software Engineering PPoPP 2003, , San Diego Synchronization  No special mechanism needed for client to resynchronize with supplier after separate call.  The client will wait only when it needs to: x.f x.g (a) y.f … value := x.some_query  This mechanism is called wait by necessity.

Chair of Software Engineering PPoPP 2003, , San Diego Two-level architecture of SCOOP  SCOOP can be implemented in several environments  Microsoft.NET is our current platform SCOOP platform-independent.NET Compact Framework POSIX Threads …

Chair of Software Engineering PPoPP 2003, , San Diego Future work  Extension of access control policy  multiple locking of separate objects based on the concept of pure functions  Instruction-level parallelism  Deadlock prevention  Extending SCOOP for real-time systems  duel mechanism with priorities  timing assertions

Chair of Software Engineering PPoPP 2003, , San Diego Conclusion SCOOP model is simple yet powerful  Full concurrency support  Full use of object-oriented techniques  Just one new keyword separate  Based on Design by Contract  Several platforms and architectures

Chair of Software Engineering PPoPP 2003, , San Diego Scoop it up! PostDoc and RA/PhD positions available At the Chair of Software Engineering, ETH Zurich, lead by Bertrand Meyer  SCOOP project (PostDoc/RA)  Formal methods for O-O programming (RA)