ThreadError: can't be called from trap context

[yourtallness]

I'm trying to follow this guide with ruby 2.4.6 & rails 4.2.11.1.

On my locally running sidekiq instance it does not seem to work:

bundle exec rbtrace -p <pid> -e "load 'command.rb'"

I've put the following line in command.rb to work around the Mac OS line-too-long issue:

Thread.new{GC.start; require "objspace";io=File.open("/tmp/ruby-heap.dump", "w"); ObjectSpace.dump_all(output: io); io.close}

In my application.rb I have:

require 'rbtrace'
require 'objspace'
ObjectSpace.trace_object_allocations_start

Yet, the result I get is:

*** attached to process 24295
>> load 'yolo.rb'
=> #<ThreadError: can't be called from trap context>
*** detached from process 24295

Please advise how I can get around this, thanks in advance.