37 lines
1.6 KiB
Racket
37 lines
1.6 KiB
Racket
#lang syndicate/actor
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;; Example showing an interesting design flaw (?) (bug?) in the
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;; old-school LLL demand-matcher when demand changes too quickly. The
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;; port 6000 server is started, but by the time it starts monitoring
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;; demand for its services, the demand is already gone, replaced with
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;; demand for port 5999. This causes connections to be accepted on
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;; port 6000 going nowhere.
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;;
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;; One fix is to use #:assertions to give the TCP listener actor some
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;; initial interests, thus transferring responsibility atomically.
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;; Another is to modify the demand-matcher to do something like
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;; `during/spawn` is doing, using an auxiliary protocol to centralise
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;; tracking of demand and supply at the demand-matcher rather than
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;; delegating it to the services.
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(require syndicate/protocol/advertise)
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(require/activate syndicate/drivers/tcp)
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(struct listen-port (number) #:prefab) ;; assertion
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(define default-port 6000)
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(spawn #:name 'connection-acceptor
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(define/query-value port default-port (listen-port $v) v)
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(assert (advertise (observe (tcp-channel _ (tcp-listener (port)) _))))
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(during (advertise (tcp-channel $c (tcp-listener (port)) _))
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(let ((accepted-port (port))) ;; capture field value at time of connect
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(assert (advertise (tcp-channel (tcp-listener accepted-port) c _)))
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(on-start
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(printf "Accepted connection from ~v on port ~a\n" c accepted-port)
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(send! (tcp-channel (tcp-listener accepted-port) c #"Hello!\n")))
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(on-stop
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(printf "Closed connection ~v on port ~a\n" c accepted-port)))))
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(spawn #:name 'configuration-provider
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(assert (listen-port 5999)))
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