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![Web sockets
Wraps http request with handler
ZnServer default delegate: (ZnWebSocketDelegate handler:
[ :webSocket |
[ | message |
message := webSocket readMessage.
webSocket sendMessage: message ] repeat ]).](https://image.slidesharecdn.com/5-rpc-191104144856/85/RPC-in-Smalltalk-24-320.jpg)
![Different notification mechanisms
● Using notifySets to update the GUI
session1 addToNotifySet: leTournoi competition poules first.
session1 notificationAction: [:idSet | callbacks do: ….].
● Using Gem to gem signalling for workflow
session gemSignalAction:
[:aSession :aSignalNumber :aString |
self handleSignalFrom: aSession number: aSignalNumber string: aString].](https://image.slidesharecdn.com/5-rpc-191104144856/85/RPC-in-Smalltalk-28-320.jpg)
![Web sockets
Wraps http request with handler
ZnServer default delegate: (ZnWebSocketDelegate handler:
[ :webSocket |
[ | message |
message := webSocket readMessage.
webSocket sendMessage: message ] repeat ]).](https://image.slidesharecdn.com/5-rpc-191104144856/75/RPC-in-Smalltalk-24-2048.jpg)
![Different notification mechanisms
● Using notifySets to update the GUI
session1 addToNotifySet: leTournoi competition poules first.
session1 notificationAction: [:idSet | callbacks do: ….].
● Using Gem to gem signalling for workflow
session gemSignalAction:
[:aSession :aSignalNumber :aString |
self handleSignalFrom: aSession number: aSignalNumber string: aString].](https://image.slidesharecdn.com/5-rpc-191104144856/75/RPC-in-Smalltalk-28-2048.jpg)
More Related Content
RPC in Smalltalk
- 1. RPC in Smalltalk AnnickFron http://www.afceurope.com http://www.fencingfox.com 7/22/19@ AFC Europe - ESUG 2019 1
- 2. Distributed applications 7/22/19@ AFCEurope - ESUG 2019 2 Dunod 2015, 3rd edition Java Distributed Architecture Software consultant, not academic
- 3. 8 fallacies inDistributed Computing (Peter Deutsch 1994) • The network is reliable : redundancy, intermediate storage • Latency is zero : 30s for light between US and Europe ; latency using Ajax • Bandwidth is infinite : packets are limited in size • The network is secure : must understand firewalls, passwords,etc. • Topology doesn't change : endpoints, alias, abstract naming, host names... • There is one administrator : monitoring, interoperability contracts • Transport cost is zero : routers, servers... • The network is homogeneous : try to stick to standards 7/22/19@ AFC Europe - ESUG 2019 3
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- 6. RPC is hard: all weapons welcome! 7/22/19@ AFC Europe - ESUG 2019 6
- 7. Sockets : don'tunderstand objects ! ● UDP ● Allows broadcast ● Limited size messages ● Faster (no handshake) ● Used by video ● TCP ● More “reliable” because of handshake... but less tolerant to network disconnection ● Used by HTTP Swiss Army knife for ANY language !
- 8. RPC ? • Remote ProcedureCall • Remote events • Data sharing • Streaming and web sockets • Remote notification • And then non functional properties : redundancy, security, reliability, resource pooling... 7/22/19@ AFC Europe - ESUG 2019 8
- 9. RPC ● Contact point: URL, registry key, endpoint(web service); – extensions to pool of workers or security policies ● Transport : TCP, UDP, HTTP, MQ ... ● Marshalling/unmarshalling
- 10. Marshalling/unmarshalling Sockets are flat • ASN1,CDR • JSON • XML • Fuel, SIXX, BOSS • Object references • 7/22/19@ AFC Europe - ESUG 2019 10
- 11. Naive ideas ● UsingdoesNotUnderstand for proxies to modify behaviour ● An object is always able to perform a selector passed as a string
- 12. Passing by reference/ by value ● Reference ● Easy for large objects ● May imply handling distributed GC ● Client and server in sync ● Ping pong effect for nested objects ● Implies a registry to one or more root references ● Value ● Client may work independently, but looses sync on server ● Large chunks being passed on the network
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- 16. Some questions ● Passingclasses ? Passed by name. But a class in one instance is recognized as a class in the other instance. This is not true in other languages Corba on C requires mapping of vtables). In Java a class in a class loader is different from the same class in another class loader, or in another memory space. Strong typing is a looser across memory spaces ● Passing errors ? Errors raise errors on the distant image ● Instvars can have individual passing policies (or none)
- 17. Distributed events andbroadcast
- 18. RPC in VW ●Pluggable transport : TCP, UDP ● Mapping to historical CORBA, IIOP : may call other languages like Java, C++ or C ● I3S provides transparent RPC with custom instvar policies (value, reference) ● Event service allows remote event notification
- 19. Seamless in Pharo ●Pass by reference or pass by value semantics ● Used for remote debug ● Initial reference : Whole environment
- 21. Both semantics supported Object>>seamlessDefaultTransferStrategy ^SeamlessTransferStrategydefaultByReference Number>>seamlessDefaultTransferStrategy ^SeamlessTransferStrategy defaultByValue
- 22. JRPC : usingJSON for marshalling
- 23. Preparing an imagefor remoting ● Identify system objects (CairoContext, files, processes …) which can't pass though ● Analyse the calling sequence to minimize ping pong : can require creating new objects which are “summaries” of some other objects, like views in a database ● Decide on pass by value/ pass by reference ● Always release ressources
- 24. Web sockets Wraps httprequest with handler ZnServer default delegate: (ZnWebSocketDelegate handler: [ :webSocket | [ | message | message := webSocket readMessage. webSocket sendMessage: message ] repeat ]).
- 25. Web sockets ● Sameissues as sockets : strings and byte arrays, no objects ● One web socket per page needs to be parsed to different fields ● Handling disconnections
- 26. Web services ● Marshalling:XML ● Endpoint : URL ● WSDL : IDL ● Transport : HTTP ● Copy semantics ● SOAP Envelope for non functional aspects (?)
- 27. Using Gemstone ● Mayuse Gemstone as a distributed shared memory ● Objects are shared in the images ● But notification of change needed to update interface : use of notifySets with the interface as a callback ● Use gemstone signalling between computers
- 28. Different notification mechanisms ●Using notifySets to update the GUI session1 addToNotifySet: leTournoi competition poules first. session1 notificationAction: [:idSet | callbacks do: ….]. ● Using Gem to gem signalling for workflow session gemSignalAction: [:aSession :aSignalNumber :aString | self handleSignalFrom: aSession number: aSignalNumber string: aString].
- 29. Conclusion ● Missing testingtools ! ● MQTT, gRPC (Google) ● Streaming : mixing data and signals