Switch to ActiveSupport::Notifications.monotonic_subscribe

[tgwizard]

Goal

This is a small performance improvement. monotonic_subscribe behaves the same as subscribe, except that the timestamps are computed slightly more efficiently. Since we don't use the timestamps here at all, there should be no impact for Bugsnag.

Design

See this benchmark:

Benchmark.ips do |x|
  x.report("Time.now") { Time.now }
  x.report("Process.clock_gettime") { Process.clock_gettime(Process::CLOCK_MONOTONIC) }

  x.compare!
end

ruby 3.3.5 (2024-09-03 revision ef084cc8f4) +YJIT [arm64-darwin23]
Warming up --------------------------------------
            Time.now     1.619M i/100ms
Process.clock_gettime
                         2.191M i/100ms
Calculating -------------------------------------
            Time.now     17.496M (± 1.7%) i/s   (57.15 ns/i) -     89.054M in   5.091258s
Process.clock_gettime
                         21.589M (± 2.0%) i/s   (46.32 ns/i) -    109.528M in   5.075753s

Comparison:
Process.clock_gettime: 21588547.9 i/s
            Time.now: 17496424.0 i/s - 1.23x  slower

Changeset

Testing

[mclack]

Hi @tgwizard

Thanks for raising this PR with us.

This seems like a sensible change. We'll make sure to give this a full review when priorities allow.