Using The .NET Framework

Distributed Shared Memory
Using The .NET Framework

Thomas Seidmann

Department of Computer Science and Engineering

Faculty of Electrical Engineering and Information Technology

Slovak University of Technology

seidmann@dcs.elf.stuba.sk

http://www.cdot.ch/thomas/

Building distributed applications
with .NET (1)

•
(lower
-
level) socket programming

•
.NET Remoting

•
Web Services

•
Concentration on RPC
-
style client/server
relationship

•
Remote access to shared objects
(methods, properties)
provided by

a
server (UDDI, manual discovery)



Middleware for
distributed objects

Node 1

Node 2

Server

Building distributed applications
with .NET (2)

•
Desired scenario: peer .NET applications
collaborate on a set of shared objects

•
Replication of objects

•
Local access to methods (and properties)

•
Provide the notion of objects
shared
among

peer .NET applications

•
Semantics of an object based DSM
(Distributed Shared Memory)
–

coherence!


Node 1

Node 2

Node 3

Node 4

coherence
protocol

Consistency model and coherence
protocol

•
Causal consistency model

•
Multiple Reader Multiple Writer (MRMW)

•
Write
-
update protocol

•
Multicast transfer of
diffs

between nodes

•
Causality relationship achieved by
vector
logical clocks
-

Associative array of pairs
(PID, value)

•
Shared object identification with a
GUID

DSM Implementation Outline

•
Mechanism for obtaining the state of a
shared object

•
Registration of every change of a shared
object in a local storage

•
Listening to changes made by remote
nodes and to object state queries

DSM Implementation Outline

•
Mechanism for obtaining the state of a
shared object

serialization

•
Registration of every change of a shared
object in a local storage
interception

•
Listening to changes made by remote
nodes and to object state queries

coherence thread


Serialization, Interception

•
[serializable]

•
Binary serialization formatter

•
TransparentProxy

•
RealProxy

DSMProxy

•
Method Entry: object
diff

storage cheched

•
Method Exit:
diff

calculated; if nonzero,
then added with the vector logical clock
value to the storage

Coherence Thread

•
Accesses object diff storage and the
shared object via its
DSMProxy

•
Performs state changes according to
remote write update messages

•
Sends write update messages

•
Requests other nodes to send write
update messages (new shared object,
timeout)

DSM Implementation Overview

Multicast Channel Service

•
Object
diffs

transported with .NET
Remoting

•
Built
-
in channels are TCP
-
based

•
IP
-
Multicast uses UDP as transport
protocol

•
UdpChannel
,
Implements
IChannel

Programming Model for Shared
Objects (1)

•
Descendant of
ContextBoundObject

•
Must be serializable

•
Annotated with
ProxyAttribute

specifying
McastDSM.DSMProxy

•
(State
-
Modifying public methods annoted
with
McastDSM.ModifiesStateAttribute)

Programming Model for Shared
Objects (2)

using System;

using System.Runtime.Remoting;

using System.Runtime.Remoting.Proxies;

using McastDSM;


[Proxy(DSMProxy)]

[serializable]

public class MySharedObject : ContextBoundObject, ISharedObject {


private Guid myGuid = null;


public Guid GuidProp {


get {return myGuid;}


set {myGuid = value;}


}


public int myMethod(string) {


//... do something with string


return 0;


}

}

Programming Model for Shared
Objects (3)

using System;

using System.Runtime.Remoting;

using System.Runtime.Remoting.Channels;

using McastDSM;

using McastDSM.Channels;


public class App {


public static int Main(string[] args) {


ChannelServices.RegisterChannel (


new UdpChannel());



// Create an instance of a


// MySharedObject class


MySharedObject myObj = new MySharedObject;


myObj.GuidProp = "478280B9
-
874E
-
4795
-
B3C7
-
05CFDD96CD2C";


myObj.myMethod("Hello World");


return 0;


}

}

Conclusions

•
100% managed code, compatible with
Rotor

•
Tested with well
-
known scientific
applications (FFT
-
3D, Barnes Hut)

•
LAN environment, simulated loss of
messages (trafic shaping with FreeBSD)

•
First focus on TRANSPARENCY

•
Comfortable programming model

Future Work

•
Second focus is on PERFORMANCE (diff
calculation, message throughput)

•
Trade
-
off between transparency and
performance

•
Other serialization formatters are being
considered (SOAP)
–

might provide better
diffs

•
SOAP together with XML aware
compression (
XMill)
?

Thank you very much for your
attention

http://www.cdot.ch/thomas/