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SCOOP: an introduction

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Title: SCOOP: an introduction

1
SCOOP an introduction

Bertrand Meyer
Chair of Software Engineering,
ETH Zurich, Switzerland
http//se.inf.ethz.ch

2
Why SCOOP?

Extend object technology with general and
powerful concurrency support
Provide the industry with simple techniques for
parallel, distributed, internet, real-time
programming
Make programmers sleep better!

3
The SCOOP model

Simple Concurrent Object-Oriented Programming
High-level concurrency mechanism
Fully uses inheritance and other O-O techniques
Applicable to many physical setups
multiprocessing, multithreading, distributed
execution, Web services...
Based on Design by Contract and Eiffel concepts

4
Object-oriented computation
Actions
Objects
Processor

To perform a computation is
to use certain processors
to apply certain actions
to certain objects.

5
What makes an application concurrent?

Processor
autonomous thread of control supporting
sequential execution of instructions on one or
more objects
Can be implemented as
Process
Thread
AppDomain (.NET)
Web service

Actions
Objects
Processor
6
Feature call synchronous

x CLASS_X
...
x.f (a)

Object 1
Object 2
f (a A) require a / Void ensure
not a.empty
previous_instruction
x
.
f
(
a
)
next_instruction
(
CLASS_T
)
(CLASS_
X
)
Processor
7
Separate feature call (asynchronous)

x separate CLASS_X
...
x.f (a)

Object 1
Object 2
f (a A) require a / Void ensure
not a.empty
previous_instruction
x
.
f
(
a
)
next_instruction
(
CLASS_T
)
(CLASS_
X
)
Processor 2
Processor 1
8
Access control policy

Target of separate call must be formal
argument of enclosing routine
store (buffer separate BUFFER INTEGER
value INTEGER) is
-- Store value into buffer.
do
buffer.put (value)
end
Call with separate argument gives exclusive
access
store (my_buffer, 10)

9
Contracts in Eiffel

store (buffer BUFFER INTEGER value INTEGER)
is
-- Store value into buffer.
require
not buffer.is_full
value gt 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)

Precondition
10
From preconditions to wait-conditions

store (buffer separate BUFFER INTEGER value
INTEGER)
is
-- Store value into buffer.
require
not buffer.is_full
value gt 0
do
buffer.put (value)
ensure
not buffer.is_empty
end
...
store (my_buffer, 10)
If buffer is separate,.

On separate target, precondition becomes
wait condition
11
Wait by necessity

No special mechanism 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

Wait here!
12
Duels

Problem Impatient client (challenger) wants to
snatch object from another client (holder)
Cant just interrupt holder, service challenger,
and resume holder would produce inconsistent
object.
But can cause exception, which will be handled
safely.

13
Duels
Challenger ? ? Holder normal_service immediate_service
retain Challenger waits Exception in challenger
yield Challenger waits Exception in holder serve challenger
14
Mapping processors to physical resources

Concurrency Control File (CCF)
create
system
"lincoln" (4) "c\prog\appl1\appl1.e
xe"
"roosevelt" (2) "c\prog\appl2\appl2.dll"
"Current" (5) "c\prog\appl3\appl3.dll"
end
external
Database_handler "jefferson" port 9000
ATM_handler "gates" port 8001
end
default
port 8001 instance 10
end

15
Two-level architecture of SCOOP

Can be implemented on various platforms
Microsoft .NET is our reference platform

16
SCOOPLI Library for SCOOP

Library-based solution
Implemented in Eiffel for .NET
(from Eiffel Software
EiffelStudio / ENViSioN! for Visual Studio.NET)
Aim try out solutions without bothering with
compiler issues
Can serve as a basis for compiler implementations

17
SCOOPLI concepts

separate client
separate supplier
Each separate client separate supplier handled
by different processor
Class gets separateness through multiple
inheritance

18
SCOOPLI emulation of SCOOP concepts
SCOOP SCOOPLI
x separate X x X -- class X is separate x SEPARATE_X -- SEPARATE_X inherits from X and -- SEPARATE_SUPPLIER
r (x, y) -- x and y are separate r (x separate X y separate Y) is require not x.is_empty y.count gt 5 i gt 0 -- i non-separate x / Void do ... end separate_execute (x, y, agent r (x, y), agent r_precondition) r_precondition BOOLEAN is do Result not x.is_empty and y.count gt 5 end -- client class inherits from -- class SEPARATE_CLIENT
19
SCOOPLI Architecture

SEPARATE_HANDLER locking checking wait
conditions scheduling of requests
PROCESSOR_HANDLERs execute separate calls
implement processors

20
Example Dining philosophers

class PHILOSOPHER inherit
PROCESS
rename
setup as getup
redefine step end
feature BUTLER
step is
do
think eat (left, right)
end
eat (l, r separate FORK) is
-- Eat, having grabbed l and r.
do end
end

21
Example Bounded buffer usage

Usage of bounded buffers
buff BUFFER_ACCESS MESSAGE
my_buffer BOUNDED_BUFFER MESSAGE
create my_buffer
create buff.make (my_buffer)
buff.put (my_buffer, my_message)
buff.put (my_buffer, her_message)
my_query buff.item (my_buffer)

22
Example elevator
Client
Inheritance
For maximal concurrency, all objects are separate
23
Dynamic diagram
1
CABIN_BUTTON
ELEVATOR
asynchronous call
4
2
synchronous call
3
ENGINE
GUI_MAIN_WINDOW
Scenario Pressing the cabin button to move the
elevator
1 Cabin button calls elevator.accept (target)
2 Elevator calls engine.move (floor)
3 Engine calls gui_main_window.move_elevator
(cabin_number, floor)
4 Engine calls elevator.record_stop (position)
24
Class BUTTON