Simple Asynchronous Remote Invocations

for Distributed Real-Time Java*

Pablo Basanta-Val, Marisol García-Valls, and Iria Estévez-Ayres

Jornadas de tiempo real 2010- Granada 4 y 5 de febrero de 2010

* Trabajo publicado en IEEE Trans. on Industrial Informatics

Outline

• Context– Synchronous models

• Synchronous remote invocations

– Proposed asynchronous model• Client-side remote invocations• Server-side remote invocations

• Some results• Conclusions and future work

2JTR-2010

Real-time Java in industrial environments

• The use of Java in industrial application is challenging– E.g. garbage collection, byte-code portability

• Giving a well-balanced to these challenges is essential to be have a successful technology– The better the architectonical challenges are

solved, the better infrastructure available

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Asynchronous communications for distributed real-time Java

• Idea:• “A remote invocation where a client does

not wait for a response of a server”• Ideal for signaling purposes

• Current status:• DRTSJ supports distributed event

– However they are implemented using synchronous remote invocations• CORBA supports the model

– One-way invocations and AMI (Asynchronous Method Invocation)• Solutions well-known in other domains [Volker 06]

– FIRE-AND-FORGET, SYNC-WITH-SERVER, POLL-OBJECT, and RESULT-CALLBACK

• Therefore:• Lets add some [simple] support for [simple] cases in DRT-Java[ FIRE-AND-FORGET, SYNC-WITH-SERVER, RESULT-CALLBACK, and POLL-OBJECT]

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Current [synchronous] remote invocations

remote objectstub

application

mid_dis_stub_invoke

remote

2 3

5

6

4

7

1

client server

mid_dis_remoteobject_invoke

Exported objects table

7654321

1.. CCCCCCCsyncRI Invocation Rate:

(1→2→3→4→5→6→7)Model:

5

JTR-2010

Client-side asynchronous remote invocations

Invocation Rate:

((1→2→6→7)||(3→4→5)).Model:

remoteobjectstub

application

remote2 3

5

6

4

7

1

client server

mid_dis_stub_invoke

mid_dis_remoteobject_invoke

7621

1.. CCCCasyncclientRI

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remoteobjectstub

application

remote2 3'

5'’6

4

7

1

client server

3'’

mid_dis_stub_invoke

mid_dis_remoteobject_invoke

5'

Server-side asynchronous remote invocations

Invocation Rate:

((1→2→3’→5’’→6→7)||(3 →4→5’)).′Model:

'''1

53621.. CCCCCasyncserverRI

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Middleware Specific Extensions

• Language (RMI Spec) issues– Changes in the semantics of a remote exception

( they are not transferred back in async. Invocations)

• New methods required and policies– setAync, getAsync methods– A-A, A-S, S-A and S-S

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package es.uc3m.it.drequiem.rtrmi.server;import javax.realtime.*;import es.uc3m.it.drequiem.rtrmi.*;import java.rmi.server.RemoteStub;public class RealtimeUnicastRemoteStub { ... public static void setParameters( RemoteStub stub,

boolean async,SchedulingParameters sp,ReleaseParameters rp,MemoryParameters mp,ProcessingGroupParameters pgp,ConnectionPool cpool)

... public static boolean getAsync(RemoteStub stub); public static void setAsync(RemoteStub stub, boolean async);...}

Middleware Specific Extensions

• Changes in the JRMP protocol

• Client and server side implementation diagrams

Message:RtCallCallPingDgcAck

RtCall:0x55 priority noheap mid async oid Call0x55 priority noheap mid async oid Ping0x55 priority noheap mid async oid DgcAck

async:boolean

Result: ProtocolRTAck ProtocolAck #Serv-side synch and synch ProtocolAck null #Client-side asynchProtocolRTAck: 0x55 priority noheap

readAsyncFlag* writeParams+

readResults+

Y

N

asynch==true

*new+extended

readAsyncFlag*readParams+

Y

Y

*new+modified

AA or AS?*

upCall

ACK upCall

upCall

N

N

flag==asynch?*

writeResults+

client-async

server-async

sync invocation

client server

RTCall RTACK

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DREQUIEMI

JTIME-VM

TimeSys-OS

TCP-IP

Client

796 Mhz

DREQUIEMI

JTIME-VM

TimeSys-OS

TCP-IP

Remoteobject

796 Mhz

Delay (0-2 ms)

Work (0-2 ms)

Data:(-1,0,...100)

Doubles

DRQTracer

EEthereal

net

Protocol: Synch

Sever-side asynch Client-side asynch

Empirical results

• Goals– I.R.sync vs I.R.async

– Client vs server async

• Taking into account • response time, • memory allocated, • bandwidth

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Memory

Bandwidth Response-time

Best platform results: <0,0,0>

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Response-time: data,<latency,work>

120

3958

7796 0 1

000

2000

2

3

4

5

6

7

8

N.I.R.

Sent Doublesdelay + work

Client-side Asynch <0-2 ms,0 >, Client-side Asynch <0,0-2 ms >

2-3 3-4 4-5 5-6 6-7 7-8

1

20

3958

7796

01000

2000

1.4

1.6

1.8

2

2.2

2.4

N.I.R.

Sent Doubles

delay

Server-side Asynch <0-2 ms ,0 >

1.4-1.6 1.6-1.8 1.8-2 2-2.2 2.2-2.4

120

3958

7796 0 1000

2000

2

2.5

3

3.5

4

4.5

N.I.R.

Sent Doubles

work

Server-side Asynch <0,0-2 ms >

2-2.5 2.5-3 3-3.5 3.5-4 4-4.5

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Client vs. Server-side async

1 1121 31 41

51 6171 81

910

1000

2000

1

1.2

1.4

1.6

1.8

Ratio

Sent Doubles

work

N.I.R. client-side/N.I.R. server-side<0,0-2000 us>

1.6-1.8

1.4-1.6

1.2-1.4

1-1.21 11 21 31

41 51 6171 81

910

1000

2000

123

4

5

6

ratio

Sent Doubles

delay

N.I.R. client-side/N.I.R. server-side<0-2000us,0>

5-6

4-5

3-4

2-3

1-2

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Conclusions and future work

• Analyzed the integration of asynchronism in DRTJava – Changes required not too complex– Client response-time strongly depends on the

[sync, async]remote invocation model used

• Ongoing work– POOL-OBJECT and RESULT-CALLBACK

– IEC-61499 and RTSJ

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