bmbm

Sometimes benchmark results are skewed because code executed earlier encounters different garbage collection overheads than that run later. #bmbm attempts to minimize this effect by running the tests twice, the first time as a rehearsal in order to get the runtime environment stable, the second time for real. GC.start is executed before the start of each of the real timings; the cost of this is not included in the timings. In reality, though, there’s only so much that #bmbm can do, and the results are not guaranteed to be isolated from garbage collection and other effects.

Because #bmbm takes two passes through the tests, it can calculate the required label width.

      require 'benchmark'

      array = (1..1000000).map { rand }

      Benchmark.bmbm do |x|
        x.report("sort!") { array.dup.sort! }
        x.report("sort")  { array.dup.sort  }
      end

Generates:

       Rehearsal -----------------------------------------
       sort!  11.928000   0.010000  11.938000 ( 12.756000)
       sort   13.048000   0.020000  13.068000 ( 13.857000)
       ------------------------------- total: 25.006000sec

                   user     system      total        real
       sort!  12.959000   0.010000  12.969000 ( 13.793000)
       sort   12.007000   0.000000  12.007000 ( 12.791000)

#bmbm yields a Benchmark::Job object and returns an array of Benchmark::Tms objects.