RubyTapas #147 - #151

147 Atomicity

★

10 x 100のincremental counter

jrubyだと期待通りにならない

lock    = Mutex.new
...
   # in multi threads
   lock.synchronize do counter += 1 end`

atomic gem

require "atomic"
counter = Atomic.new(0)
...
  counter.update{|c| c + 1}

atomicのperformanceはMRIだと遅いがjrubyだと速い

148 Rake Invoke

★★★

rakeの実行

require "rake"
Rake.application.init
Rake.application.load_rakefile
Rake::Task["hello"].invoke
# >> Hello from Rakefile

Rake::Task["hello"].invokeは2回書いても1度しか走らない

Rake::Task["hello"].executeなら再実行できる

ruleも実行 Rake::Task["hello.html"].invoke

149 Sum

★★

with Rails (ActiveSupport)

[1,2,3].sum

Without rails -> reduce/inject

sum = data.reduce(0) {|acc, n| acc + n }

add = :+.to_proc
add.call(2, 2)

sum = data.reduce(0, &:+)
sum = data.reduce(0, :+)
sum = data.reduce(:+)

XOR

data = [1,2,3,4,5,6,7,8,9,10]
checksum = data.reduce(:^)      # => 11

150 Stats

★★

median

sorted = data.sort
half_size = sorted.size / 2
middle = if sorted.size.even?
           sorted[half_size - 1, 2]
         else
           sorted[half_size, 1]
         end
med = middle.reduce(:+) / middle.size

sorted = data.sort
half_size = sorted.size / 2
q, r = sorted.size.divmod(2)
middle = sorted[q - 1 + r, 2 - r]
med = middle.reduce(:+) / middle.size 

standard deviation

std = Math.sqrt(data.map{|n| (n - avg) ** 2}.reduce(:+) / data.size)
std

151 Sleep

★★★

How accurate is #sleep?

MRI

$ ruby test-sleep.rb 0.001 1 
Actual length: 1.0832039779999998 seconds
Max: 0.002941898

$ ruby test-sleep.rb 0.0001 1
Actual length: 1.5849713390000042 seconds
Max: 0.001965845

$ ruby test-sleep.rb 0.00001 1
Min: 1.7454e-05

jruby, rubinius

$ rvm jruby,rbx --verbose do ruby test-sleep.rb 0.001 1
jruby-1.7.4
Actual length: 1.1180506600000006 seconds
Max: 0.00272422

rbx-head: rubinius 2.0.0rc1
Actual length: 1.083565672999999 seconds
Max: 0.004236704

トータルはRubiniusがMRIに近く正確、Max(外れ値は)jrubyの方が小さい

$ rvm jruby,rbx --verbose do ruby test-sleep.rb 0.0001 1
jruby-1.7.4
Actual length: 0.05607388499999989 seconds
Min: 2.002e-06
Max: 0.000120069

rbx-head: rubinius 2.0.0rc1
Actual length: 1.6065821489999945 seconds
Min: 0.000108257
Max: 0.00405398

RubiniusはMRIに近い、jrubyは極端に短い値(Actual length)になった