FakeMutex

Eric Hodel | Wed, 11 Jan 2006 01:23:00 GMT

Posted in Robot Co-op, Ruby

Adding Mutex makes things slower, but you don’t always need it. For our memcache library I’d like to avoid performing locking when we’re running single-threaded (since that’s what happens most of the time). So, I came up with the idea of FakeMutex that simply yields inside its #synchronize method.

FakeMutex doesn’t give back all the performance of not having locking at all, but it does prevent the code from being messed up with lots of tests to see if we should try to lock or not.

require 'benchmark'
require 'thread'

class FakeMutex
  def synchronize
    yield
  end
end

N = 1_000_000

Benchmark.bmbm do |bm|

  fake = FakeMutex.new
  real = Mutex.new

  bm.report 'NoMutex' do
    N.times do
      1 + 1
    end
  end

  bm.report 'FakeMutex' do
    N.times do
      fake.synchronize { 1 + 1 }
    end
  end

  bm.report 'RealMutex' do
    N.times do
      real.synchronize { 1 + 1 }
    end
  end

end

Rehearsal ---------------------------------------------
NoMutex     0.870000   0.000000   0.870000 (  1.004429)
FakeMutex   2.350000   0.020000   2.370000 (  2.555904)
RealMutex   8.770000   0.030000   8.800000 (  9.433895)
----------------------------------- total: 12.040000sec

                user     system      total        real
NoMutex     0.780000   0.010000   0.790000 (  0.820284)
FakeMutex   2.350000   0.010000   2.360000 (  2.536308)
RealMutex   8.780000   0.050000   8.830000 ( 10.722575)