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Re: [Chicken-users] socket egg: socket-receive blocks?

From: Jim Ursetto
Subject: Re: [Chicken-users] socket egg: socket-receive blocks?
Date: Fri, 14 Jun 2013 16:58:58 -0500

Should be fixed in 0.2.3.  Let me know.


On Jun 14, 2013, at 3:24 PM, Jim Ursetto <address@hidden> wrote:


It's a bug in the socket egg; nonblocking mode is only set during a socket-connect or socket-accept, which won't be called for UDP.

Temporary workaround: (use posix) and then, after creating the socket, do either:

(##sys#file-nonblocking! (socket-fileno *socket*))

or equivalently

(file-control fcntl/setfl (socket-fileno *socket*)
 (bitwise-ior (file-control fcntl/getfl (socket-fileno *socket*))

Neither workaround will work on Windows.

Permanent fix: We should probably make all sockets nonblocking at creation time instead, since our machinery assumes nonblocking sockets.  We could expose the set-nonblocking operation to the user, but since TCP is always nonblocking, doing this only for UDP would be strange.  Thoughts?


On Jun 14, 2013, at 11:01 AM, Kristian Lein-Mathisen <address@hidden> wrote:

Hi Chickeners!

I have come across a problem with multiple srfi-18 threads when tryping to listen to UDP sockets:

(use socket)
(set! *socket* (socket af/inet sock/dgram ))
(set! (so-reuse-address? *socket*) #t)
(socket-bind *socket* (inet-address "" 5055))
;; (socket-receive ..) here blocks the prints below
;; after 1 s (about 10 hello's)
(thread-start! (lambda ()
                 (thread-sleep! 1)
                 (print "receiving ...")
                 (print (socket-receive *socket* 1024))
                 (print "done")))

(let loop ()
 (print "hello from main-thread!")
 (thread-sleep! .1)

;; the hello's from the main thread continue after sending a udp packet:
;; $ echo test `date` | socat - UDP-DATAGRAM:,broadcast

The documentation for socket clearly states that socket-receive should not block:
This call will block until data is available, but other threads can proceed.

What is wrong with my socket fd?

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