pkg/54103: "rust never sleeps" wrong on one of my machines

[bernhard%netmuc.net@localhost]

>Number:         54103
>Category:       pkg
>Synopsis:       "rust never sleeps" wrong on one of my machines
>Confidential:   no
>Severity:       non-critical
>Priority:       medium
>Responsible:    pkg-manager
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Sat Apr 06 14:20:00 +0000 2019
>Originator:     Bernhard Riedel
>Release:        NetBSD-8.99.36/amd64 as of April 4, pkgsrc-2019Q1
>Organization:
>Environment:
NetBSD tja.crg.de 8.99.36 NetBSD 8.99.36 (GENERIC) #0: Wed Apr  3 18:57:32 CEST 2019  root%wip.crg.de@localhost:/sdata/test-current-20190403000000Z/obj/amd64/sys/arch/amd64/compile/GENERIC amd64

>Description:
Hi,

when building pkgsrc/lang/rust on one of my machines, I could observe
 long pauses with load = 0.00, 0.00, 0.00 and rustc waiting:

  PID USERNAME PRI NICE   SIZE   RES STATE      TIME   WCPU    CPU COMMAND
 3535 root      85    0   244M   71M 3535 7/9   0:00  0.00%  0.00% rustc

This could go on for quite some time, but I stumbled over a workaround.
Typing a few characters in an unused console or sshing in a few times
 would end rustc's siesta.

Suspicion: rustc could be hungry for entropy and maybe uses /dev/random
 instead of /dev/urandom.

Why am *I* seeing this? That box doesn't have any sdN or wdN, only an ld0
 attached to nvme, and there is no mouse attached either.
As confirmed by 'rndctl -l', nvme/ld0 aren't used as entropy sources.

Cheers, Bernhard Riedel.

>How-To-Repeat:
See above. When trying to repeat, the pauses don't always happen for the same source files.
>Fix: