Commits on Oct 30, 2021

1. Add new Performance/ConcurrentMonotonicTime cop …

   Follow up to rails/rails#43502.
   
   This PR adds new `Performance/ConcurrentMonotonicTime` cop.
   
   This cop identifies places where `Concurrent.monotonic_time`
   can be replaced by `Process.clock_gettime(Process::CLOCK_MONOTONIC)`.
   
   ```ruby
   # bad
   Concurrent.monotonic_time
   
   # good
   Process.clock_gettime(Process::CLOCK_MONOTONIC)
   ```
   
   Below is a benchmark.
   
   ```ruby
   % cat monotonic_time.rb
   #!/usr/local/bin/ruby
   
   p `ruby -v`
   
   require 'concurrent'
   require 'benchmark/ips'
   
   Benchmark.ips do |x|
     x.report('Concurrent.monotonic_time') { Concurrent.monotonic_time }
     x.report('Process.clock_gettime')     {
     Process.clock_gettime(Process::CLOCK_MONOTONIC) }
   
     x.compare!
   end
   ```
   
   ```console
   % ruby monotonic_time.rb
   "ruby 3.0.2p107 (2021-07-07 revision 0db68f0233) [x86_64-darwin19]\n"
   Warming up --------------------------------------
   Concurrent.monotonic_time
                          607.064k i/100ms
   Process.clock_gettime
                          730.862k i/100ms
   Calculating -------------------------------------
   Concurrent.monotonic_time
                             5.695M (± 4.4%) i/s -     28.532M in
                             5.019798s
   Process.clock_gettime
                             7.398M (± 2.5%) i/s -     37.274M in
                             5.041776s
   
   Comparison:
   Process.clock_gettime:  7397700.9 i/s
   Concurrent.monotonic_time:  5695385.0 i/s - 1.30x  (± 0.00) slower
   ```
   
   And this cop is compatible with ruby-concurrency/concurrent-ruby#915.

   

   koic committed Oct 30, 2021
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