2.16 Limiting Requests

procedure
( make limitinner[#:over-limitover-limit])→dispatcher/c
limit:number?
inner:dispatcher/c
over-limit:(symbols 'block'kill-new'kill-old)='block

Returns a dispatcher that defers to inner for work, but will forward a maximum of limit requests concurrently.

If there are no additional spaces inside the limit and a new request is received, the over-limit option determines what is done. The default ('block) causes the new request to block until an old request is finished being handled. If over-limit is 'kill-new, then the new request handler is killed—a form of load-shedding. If over-limit is 'kill-old, then the oldest request handler is killed—prioritizing new connections over old. (This setting is a little dangerous because requests might never finish if there is constant load.)

Consider this example:

#lang racket

(require web-server/web-server
web-server/http
web-server/http/response
(prefix-in limit:web-server/dispatchers/limit)
(prefix-in filter:web-server/dispatchers/dispatch-filter)
(prefix-in sequencer:web-server/dispatchers/dispatch-sequencer))

(serve #:dispatch
(sequencer:make
(filter:make
#rx"/limited"
(limit:make
5
(lambda (connreq)
(output-response/method
conn
(response/full
200#"Okay"
(current-seconds )TEXT/HTML-MIME-TYPE
empty
(list (string->bytes/utf-8
(format "hello world ~a"
(sort (build-list 100000(λ x(random 1000)))
< )))))
(request-method req)))
#:over-limit'block))
(lambda (connreq)
(output-response/method
conn
(response/full 200#"Okay"
(current-seconds )TEXT/HTML-MIME-TYPE
empty
(list #"<html><body>Unlimited</body></html>"))
(request-method req))))
#:port8080)

(do-not-return )

top ← prev up next →