bug#30644: Cuirass runs out of build users

[Ludovic Courtès]

Hi Danny,

Danny Milosavljevic <address@hidden> skribis:

> I've checked it some more.  The shared cache uses unlock_notify, and the 
> actual
> database uses sqlite3_busy_handler (sqlite3_busy_timeout) when BUSY is 
> returned.
>
> The 5 in
>
> ice-9/eval.scm:619:8: Throw to key `sqlite-error' with args `(#f 5 "database 
> is locked")'.  
>                                                                  ^^
>
> means SQLITE_BUSY, so that's the actual database.
>
> So the easiest way to work around it would be to call
>
>   sqlite3_busy_timeout(db, 10); // ms
>
> which would automatically repeatedly retry on busy until 10 ms have 
> accumulated,
> and only then give up.

Indeed, that’s actually what nix/libstore does.

> There's also sqlite3_busy_handler which can be used to install a busy handler,
> and of course in the future we could also handle SQLITE_BUSY ourselves and 
> yield.
>
> See also https://notabug.org/civodul/guile-sqlite3/pulls/4 for the former.

Awesome.

I’ve merged these guile-sqlite3 bits and added a “PRAGMA busy_timeout”
in Cuirass (the pragma allows us to set the timeout even when using an
older guile-sqlite3.)  I’ve updated the ‘cuirass’ package and will test
soonish on berlin.

Thank you!

Ludo’.