47 lines
1.8 KiB
Racket
47 lines
1.8 KiB
Racket
#lang scribble/manual
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@require[racket/include]
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@include{prelude.inc}
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@title{Examples}
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@section[#:tag "echo-server-example"]{TCP echo server}
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Here is a complete Marketplace program:
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@#reader scribble/comment-reader (racketmod #:file "examples/echo-paper.rkt" marketplace
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(endpoint #:subscriber (tcp-channel ? (tcp-listener 5999) ?)
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#:conversation (tcp-channel from to _)
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#:on-presence (spawn #:child (echoer from to)))
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(define (echoer from to)
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(transition stateless
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(endpoint #:subscriber (tcp-channel from to ?)
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#:on-absence (quit)
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[(tcp-channel _ _ data)
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(send-message (tcp-channel to from data))])))
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)
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The top-level @racket[endpoint] action subscribes to TCP connections
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arriving on port 5999, and @racket[spawn]s a fresh process in response to
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each (@racket[#:on-presence]). The topic of
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conversation (@racket[#:conversation]) associated with the newly-present
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subscription is analyzed to give the remote
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(@racket[from]) and local (@racket[to]) TCP addresses, which are
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passed to the @racket[echoer] function to give the initial actions for
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the corresponding process. Here, the process is stateless, using the
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special constant @racket[stateless] as its state.
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Each connection's process creates an endpoint subscribing to data
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arriving on its particular connection, using @racket[from] and @racket[to]
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passed in from the top-level @racket[endpoint]. When data arrives, it is
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echoed back to the remote peer using @racket[send-message]. Presence
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manages disconnection; when the remote peer closes the TCP connection,
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the @racket[#:on-absence] handler in @racket[echoer] issues a @racket[quit]
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action, terminating the connection's process. The heart of our system
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is the interface between a process and its containing VM. Our
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implementation instantiates this interface as a collection of Typed
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Racket programs.
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@section{TCP chat server}
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