gistfile1.txt

require 'rubygems'
require 'spec'
require 'benchmark'

describe 'File#flock' do
  before do
    @lock_file = '/tmp/xxx.lock'
  end

  after do
    File.unlink(@lock_file)
  end

  it 'should fail with same instance of File' do
    f = File.open(@lock_file, 'w')
    
    try_lock(f, f).should_not be_true
  end

  it 'should success with different instances of File' do
    f1 = File.open(@lock_file, 'w')
    f2 = File.open(@lock_file, 'w')
    
    try_lock(f1, f2).should be_true
  end

  def try_lock(f1, f2)
    threads = []

    Benchmark.measure do
      threads << Thread.new do
        sleep 1
        f1.flock(File::LOCK_EX)
        sleep 2
        f1.flock(File::LOCK_UN)
      end

      threads << Thread.new do
        f2.flock(File::LOCK_EX)
        sleep 2
        f2.flock(File::LOCK_UN)
      end

      threads.each do |thread|
        thread.join
      end
    end.real.to_i == 4
  end
end