Formalising Java RMI with Explicit Code Mobility - DJ - Distributed

36 Pages·2005·2.32 MB·English

by  Alexander Ahern

Formalising Java RMI
with Explicit Code
Mobility
Alexander Ahern
Nobuko Yoshida
Department of Computing
Imperial College London
Motivation
Distribution is important to modern object-
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oriented programming
Yet, existing formalisms are insufficient:
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Single location
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No modelling of distributed runtime
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DJ – Distributed Java
First formalisation of Java RMI
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New primitives for type-safe code mobility
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A novel proof technique for type safety of
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distributed programs
Proof of correctness of several RMI
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optimisations
3
Call Aggregation
[Bogle & Liskov 1994, Yeung & Kelly 2003]
int m1(RemoteObject r, int a) {
int x = r.f(a);
int y = r.g(a, x);
int z = r.h(a, y);
r
nt e
return z; e v
r
li e
} C S
x and y are dead from the
client’s point of view
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Call Aggregation
[Bogle & Liskov 1994, Yeung & Kelly 2003]
// Client
int m1(RemoteObject r, int a) {
(unit -> int) t = freeze() {
int x = r.f(a);
r
nt e
int y = r.g(a, x); e v
r
li e
int z = r.h(a, y); C S
return z;
};
return r.run(t);
}
// Server
int run((unit -> int) x) {
return defrost(x);
}
5
DJ – Model
DJ = Java + distribution + new primitives and types
Creates a closure
e ::= freeze(T x) { e }
| defrost(e, e)
| …
Evaluates a
T ::= T -> T | … closure
A new arrow type for
closures
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Runtime Syntax
We require lots of syntax
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Don’t worry! You don’t need to
remember this!
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Networks consist
Networks of zero or more
JVMs executing in
parallel
JVM
JVM
Virtual machines
Each machine communicate by Remote
keeps a table of Method Invocations
JVM
classes, and has a
JVM
private memory
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Remote Method Invocation
Nature of parameters affects the nature of
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remote calls
If a parameter is not a subtype of
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java.rmi.Remote, then it is passed by value
For object parameters, this requires object
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serialisation
This is the conversion of structured data into an array
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of bytes suitable for network transfer
We model all of these features in DJ
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Remote Method InvoByctesa artei on
transferred to
Deserialise
the server
0 1 1 0 bytes into
Serialise actual
structured form
parameters
Network
Network
Evaluate local
Deserialisation can trigger
method call
Bytes transferred to
class downloading
the client
1 0 1 0
Network
Network
Serialise
Return value deserialised, returned
return value
to caller
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