* guix/workers.scm (worker-thunk): Add (const #f) as the 'catch'
handler, and move previous handler as pre-unwind handler. Protect
against 'make-stack' returning #f.
Fixes <https://bugs.gnu.org/28779>.
Reported by Eric Bavier <bavier@cray.com>.
* guix/workers.scm (<pool>)[busy]: New field.
(worker-thunk): Add #:idle and #:busy and use them.
(make-pool): Pass #:busy and #:idle to 'worker-thunk'. Pass a 'busy'
value to '%make-pool'.
* guix/workers.scm (pool-idle?): Check whether 'pool-busy' returns zero
and adjust docstring.
This allows 'guix publish' threads as well as 'guix substitute' and
'guix offload' processes to be properly labeled in 'top', 'pstree', etc.
* guix/workers.scm (worker-thunk): Add #:thread-name parameter and honor it.
(make-pool): Likewise.
* guix/scripts/publish.scm (http-write): Add calls to 'set-thread-name'
in bodies of 'call-with-new-thread'.
(guix-publish): Call 'set-thread-name'. Pass #:thread-name to 'make-pool'.
* guix/scripts/offload.scm (guix-offload): Call 'set-thread-name'.
* guix/scripts/substitute.scm (guix-substitute): Likewise.
