d61eb53686
Started as fixing misindented definitions, then more indentations, then a bunch of similar things (square brackets, huge spaces at end-of-lines, etc).
77 lines
1.9 KiB
Racket
77 lines
1.9 KiB
Racket
#lang scribble/doc
|
|
@(require "web-server.rkt"
|
|
(for-label web-server/http
|
|
web-server/lang/soft
|
|
web-server/lang/web))
|
|
|
|
@title[]{Soft State}
|
|
|
|
@defmodule[web-server/lang/soft]{
|
|
|
|
Sometimes you want to reference a large data-structure from a stateless program without the data-structure being serialized
|
|
and increasing the size of the serialization. This module provides support for this scenario.
|
|
|
|
@defproc[(soft-state? [v any/c])
|
|
boolean?]{
|
|
Determines if @racket[v] is a soft state record.
|
|
}
|
|
|
|
@defproc[(make-soft-state [thnk (-> any/c)])
|
|
soft-state?]{
|
|
Creates a piece of soft state that is computed by @racket[thnk]. This value is serializable.
|
|
}
|
|
|
|
@defproc[(soft-state-ref [ss soft-state?])
|
|
any/c]{
|
|
Extracts the value associated with @racket[ss]. If the value is not
|
|
available (perhaps because of garbage collection, deserialization in an
|
|
uninitialized process, etc), then the thunk associated with @racket[ss]
|
|
is invoked and the value is cached.
|
|
}
|
|
|
|
@defform[(soft-state expr ...)]{
|
|
Equivalent to @racket[(make-soft-state (lambda () expr ...))].
|
|
}
|
|
|
|
Here's an example servlet that uses soft state:
|
|
@racketmod[
|
|
web-server
|
|
|
|
(provide interface-version start)
|
|
(define interface-version 'stateless)
|
|
|
|
(define softie
|
|
(soft-state
|
|
(printf "Doing a long computation...\n")
|
|
(sleep 1)))
|
|
|
|
(define (start req)
|
|
(soft-state-ref softie)
|
|
(printf "Done\n")
|
|
(start
|
|
(send/suspend
|
|
(lambda (k-url)
|
|
(response/xexpr
|
|
`(html (body (a ([href ,k-url]) "Done"))))))))
|
|
]
|
|
|
|
When this is run and the link is clicked a few times, the output is:
|
|
@verbatim{
|
|
$ plt-web-server -p 8080
|
|
Doing a long computation...
|
|
Done
|
|
Done
|
|
Done
|
|
Done
|
|
}
|
|
|
|
If the server is restarted or the hostname in the URL is changed to a different host with the same code, and the URL is clicked:
|
|
@verbatim{
|
|
^Cuser break
|
|
$ plt-web-server -p 8080
|
|
Doing a long computation...
|
|
Done
|
|
}
|
|
|
|
}
|