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[bug#67245] [PATCH] store: Use a non-blocking socket for store connectio
From: |
Ludovic Courtès |
Subject: |
[bug#67245] [PATCH] store: Use a non-blocking socket for store connections. |
Date: |
Sun, 26 Nov 2023 23:16:54 +0100 |
User-agent: |
Gnus/5.13 (Gnus v5.13) |
Hi Christopher,
Christopher Baines <mail@cbaines.net> skribis:
> For some applications, it's important to do this here rather than just making
> the socket non-blocking after the connection is established because there can
> be I/O on the socket that will block during the handshake.
>
> I've noticed this blocking during the handshake causing issues in the build
> coordinator for example.
>
> * guix/store.scm (open-unix-domain-socket, open-inet-socket): Pass
> SOCK_NONBLOCK when calling socket.
>
> Change-Id: I8225762b78448bc1f7b698c8de5d736e13f577bf
I feel we should really discuss on Guix + Fibers since we’ve apparently
been going through the exact same set of issues. :-)
(The other thing that comes to mind is the resource pool!)
> +++ b/guix/store.scm
> @@ -460,7 +460,9 @@ (define (open-unix-domain-socket file)
> '&store-connection-error' upon error."
> (let ((s (with-fluids ((%default-port-encoding #f))
> ;; This trick allows use of the `scm_c_read' optimization.
> - (socket PF_UNIX (logior SOCK_STREAM SOCK_CLOEXEC) 0)))
> + (socket PF_UNIX
> + (logior SOCK_STREAM SOCK_CLOEXEC SOCK_NONBLOCK)
> + 0)))
We cannot do this here because callers have to be prepared to deal with
non-blocking sockets, and that’s not the case in Guix itself.
In Cuirass, I have this:
--8<---------------cut here---------------start------------->8---
(define (non-blocking-port port)
"Make PORT non-blocking and return it."
(let ((flags (fcntl port F_GETFL)))
(when (zero? (logand O_NONBLOCK flags))
(fcntl port F_SETFL (logior O_NONBLOCK flags)))
port))
(define (ensure-non-blocking-store-connection store)
"Mark the file descriptor that backs STORE, a <store-connection>, as
O_NONBLOCK."
(match (store-connection-socket store)
((? file-port? port)
(non-blocking-port port))
(_ #f)))
(define-syntax-rule (with-store/non-blocking store exp ...)
"Like 'with-store', bind STORE to a connection to the store, but ensure that
said connection is non-blocking (O_NONBLOCK). Evaluate EXP... in that
context."
(with-store store
(ensure-non-blocking-store-connection store)
(let ()
exp ...)))
--8<---------------cut here---------------end--------------->8---
Then ‘with-store/non-blocking’ is used in fiberized context where I know
this is fine.
I think it’ll have to remain this way until Guix itself is fiberized or
something.
Does that make sense?
Ludo’.