Formal dialogues a new approach to remote object communication

Formal dialogues

• A new approach to remote object communication

• implemented as an extension to C# on ROTOR/.NET

• Raphael Güntensperger

• Jürg Gutknecht

• ETH Zürich

Agenda

• Overview

• Concepts

• Model

• Implementation

• Development platform for tiny devices (outlook)

Overview

• Communication model

• Formal dialogues

• Syntactic integration in C#

Concepts

• Motivation

• Autonomous behavior of hardware objects
• Independent activities
• Asynchronous execution
• Example: Clock
• Rich interface to the environment
• More than only a set of methods
• Dialog-based interfaces
• Objects have a status

Concepts

• A new model for remote objects

• Active Objects (activities)
• Formal Dialogues (channels)
• Universal encoding of syntactic Tokens
• No: RPC, RMI, IDL, Proxies, Marshalling

• Optimal Support by C# and .NET runtime

• Compiler integration
• Small library (System.Channels)

Concepts

• Activities

• Separate thread of control
• Member of a class
• Started at instantiation time of the object

Concepts

• More about activities

• No activity, one or more activities per class
• Derived classes can define their own activities
• All activities are started at instantiation time (incl. Base class activities) and run in parallel

Concepts

• Channels

• Vehicle for the implementation of formal dialogues
• Channel type formal dialogue Interface
• Channel instance dialogue in execution
• Channel implementation syntax parser

Concepts

• More about channels

• Remote Interface of an object
• Channel instances run in separate threads
• Opened and closed by a client
• Member of a class
• In contrast to activities:
• controlled by client
• one instance (thread) per connection
• communication capabilities (through accessors)

Concepts

• Communication follows a formal dialogue
• Exchange of syntactic tokens
• Can be described by an EBNF syntax
• bi-directional definition
• Parser defines semantic actions
• Strongly typed tokens
• Dialogue has its own status

Concepts

Concepts

• Example:

Concepts

• Advantages to Remote Method Invocation:

• Sender is not blocked
• State of the dialogue is completely captured by the channel
• Tokens are typed by the underlying grammar and encoded according to universal rules.

Model

Model

• Channel accessors:

• open Instantiate channel, invoke parser
• close abort parser thread
• send pass token to buffer of remote channel
• receive read token from buffer of remote channel
• put pass token to internal channel buffer
• get read token from internal channel buffer

Model

Model

Model

• Gateway channels

• Abstraction of a remotely available channel in the clients address space
• ONE gateway (instead of proxies)
• Implemented as member of channel manager
• ChannelManager.RemoteChannel
• Buffer content is directly sent to the remote channel manager and vice versa

Model

• Transmit Buffer-Content by channel manager
• Channel Provider: Tracking buffers of channel instances
• Client: Tracking buffers of RemoteChannel instances
• Channel instances are identified by GUID

Model

• Home Channel:

• Query for implemented protocols
• Implicitly implemented (by the compiler) for any channel provider
• Provides a query mechanism comparable to COM (IUnknown)
• Behaves exactly like any other channel but follows a fixed syntax

• Syntax

• List names of implemented channels

Implementation (Compiler)

Implementation (Compiler)

• Threading model

• Thread represents channel instance
• Buffer references stored relative to thread context
• Thread is started by open accessor

• Code example

Implementation (Library)

• Token

• Map a set of basic types: char, int, long, float, double, keyword, string, bool, block, escape
• Define their own encoding
• Basic Format: tagByte { dataByte }
• Shortest encoding for most frequently used types
• Use value bits in the tag byte (for small data types)

• Buffer

• Ring-buffer implementation
• enlarged automatically if the get full
• Limit can be specified

Implementation (Library)

• Channel manager

• Responsible to handle channel instances and map their corresponding parts (local/remote)
• Defines gateway channel
• Channel manager messages:
• Open/Close requests
• Data transmission
• Close enquiry
• Acknowledgements

Implementation (Library)

• Transport manager

• Abstract class
• Must be implemented for a specific technology
• Current implementations: TCP/IP, Nullmodem
• Must provide reliable transmission of encoded data
• Destination

Implementation (Compiler/Library)

• Implicit interface for channel providers
• Defined in library, implemented by compiler
• ChannelManager calls OpenChannel method of specific channel implementation
• OpenChannel method
• Implicitly generated by the compiler
• Maps channel names to channel types
• Returns buffer and thread references by ChannelNode structure

Implementation (Example)

Development platform for tiny devices (outlook)

• Cross compiler: IL StrongARM

• Limited to the functionality demanded by tiny devices

• Device represents active object

• Implement a specific transport technology

• Bluetooth / Smart-Its (University of Karlsruhe)

• ‘Burn’ mechanism invokes cross compiler and builds operating system environment of the small device

Reference

• .NET Developer’s Journal, Volume 01, Issue 3

• A New Approach to Remote Object Communication
• http://www.sys-con.com/dotnet/