Locking insights: an alternative to redis set nx ex / memcache add

A lock that does not timeout can lead to a standstill and manual cleanup. Simple solution: redis ‘set ex nx’ and memcached ‘add’.

When indefinite locks happen, getting information on why they happen helps to debug the locking mechanism and see if the processes always fail to unlock.

A softer locking approach to receive feedback when locks expire:

Code

def lock
  timeout = 30
  key = 'lock'
  now = Time.now.to_i
  if redis.setnx(key, "#{now}-#{Process.pid}-#{Socket.gethostname}")
    yield
  elsif (old = redis.get(key)) && now > old.to_i + timeout
    logger.error("Releasing expired lock #{old}")
    redis.delete(key) # next process can get the lock 
  end
end

Not 100% safe since the delete could cause multiple processes to get a lock, but depending on your usecase this might be an ok tradeoff.

Allowing travis to git clone by adding a public ssh key

My new on demand gem server wants to test on travis with ssh cloning, so let’s add a ssh key (from user ‘some-public-token’ that I created and does not have any projects)

#.travis.yml
before_script:
 - echo -e "Host *\n\tStrictHostKeyChecking no\n" >> ~/.ssh/config
 - echo -e "ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAABAQDkTcgXnHuqR0gbwegnr9Zxz4hTkjjV/SpgJNPJz7mo/HKNbx0rqjj1P0yGR053R9GSFFim2ut4NK9DPPUkQdyucw+DoLkYRHJmlJ4BNa9NTCD0sl+eSXO2969kZojCYSOgbmkCJx8mdgTwhzdgE/jhBrsY0hPE6pRTlU+H68/zeNdJUAIJf0LLXOm3hpTKLA19VICltl/j9VvBJpgRHdBylXEyL8HokYpjkQQk1ZXj3m7Nlo8yDdg4VcljOJWC+Xh8kxRMfK5x/VRVsYKCQXN5QlzKeqf7USRDUS/7mFoPUBW+d4kwKtGxRsWuIL2yeqzifZUTOgsh9+ZWAWxWffQZ your_email@example.com" > ~/.ssh/id_rsa.pub
 - echo -e "-----BEGIN RSA PRIVATE KEY-----\nMIIEpAIBAAKCAQEA5E3IF5x7qkdIG8HoJ6/Wcc+IU5I41f0qYCTTyc+5qPxyjW8d\nK6o49T9MhkdOd0fRkhRYptrreDSvQzz1JEHcrnMPg6C5GERyZpSeATWvTUwg9LJf\nnklztvevZGaIwmEjoG5pAicfJnYE8Ic3YBP44Qa7GNITxOqUU5VPh+vP83jXSVAC\nCX9Cy1zpt4aUyiwNfVSApbZf4/VbwSaYER3QcpVxMi/B6JGKY5EEJNWV495uzZaP\nMg3YOFXJYziVgvl4fJMUTHyucf1UVbGCgkFzeUJcynqn+1EkQ1Ev+5haD1AVvneJ\nMCrRsUbFriC9snqs4n2VEzoLIffmVgFsVn30GQIDAQABAoIBAQDPQm2sQbti0mN8\nD4Uawl8D40v30n8WhUa7EbPTOmlqKAQ2sfDhex9KRbTLEmEBmImA/Eee8o9iCTIy\n8Fv8Fm6pUHt9G6Pti/XvemwW3Q3QNpSUkHqN0FDkgecQVqVBEb6uHo3mDm4RFINX\neOmkp30BjIK9/blEw1D0sFALLOEUPaDdPMwiXtFgqfrFSgpDET3TvQIwZ2LxxTm0\ncNmP3sCSlZHJNkZI4hBEWaaXR+V5/+C1qblDCo5blAWTcX3UzqrwUUJgFi6VnBuh\n7S9Q6+CEIU+4JRyWQNmY8YgZFaAp6IOr/kyfPxTP1+UEVVgcLn3WDYwfG9og0tmz\nfzlruAgBAoGBAPfz73Pey86tNZEanhJhbX8gVjzy2hvyhT0paHg0q/H6c1VWOtUH\nOwZ3Ns2xAZqJhlDqCHnQYSCZDly042U/theP4N8zo1APb4Yg4qdmXF9QE1+2M03r\nkS6138gU/CSCLf8pCYa6pA/GmsaXxloeJGLvT4fzOZRsVav80/92XHRhAoGBAOu2\nmKh4Gr1EjgN9QNbk9cQTSFDtlBEqO/0pTepvL73UvNp/BAn4iYZFU4WnklFVBSWc\nL84Sc732xU12TAbTTUsa6E7W29pS8u7zVTxlIdQIIU5pzDyU1pNNk2kpxzte5p3Y\nPDtniPFsoYLWoH0LpsKL93t2pLAj+IOkE6f3XBq5AoGAIKaYo5N1FxQr952frx/x\nQUpK0N/R5Ng8v18SiLG26rhmM5iVSrQXC7TrHI7wfR8a9tC6qP/NqnM9NuwC/bQ0\nEEo7/GhaWxKNRwZRkmWiSFLNGk9t1hbtGU+N1lUdFtmloPIQdRNiw0kN3JTj474Q\nYI7O1EItFORnK6yxZfR6HEECgYEA1CT7MGUoa8APsMRCXyaiq15Pb8bjxK8mXquW\nHLEFXuzhLCW1FORDoj0y9s/iuKC0iS0ROX8R/J7k5NrbgikbH8WP36UxKkYNr1IC\nHOFImPTYRSKjVsL+fIUNb1DSp3S6SsYbL7v3XJJQqtlQiDq8U8x1aQFXJ9C4EoLR\nzhKrKsECgYBtU/TSF/TATZY5XtrN9O+HX1Fbz70Ci8XgvioheVI2fezOcXPRzDcC\nOYPaCMNKA5E8gHdg4s0TN7uDvKTJ+KhSg2V7gZ39A28dHrJaRX7Nz4k6t2uEBjX9\na1JidpAIbJ+3w7+hj6L299tVZvS+Y/6Dz/uuEQGXfJg/l/5CCvQPsA==\n-----END RSA PRIVATE KEY-----" > ~/.ssh/id_rsa
 - chmod 600 ~/.ssh/id_rsa*
 - eval `ssh-agent -s`
 - ssh-add ~/.ssh/id_rsa

You might might even use this trick to sneak private repo builds into public travis … but that would be evil …

Using rails 2 views in rails 3.2

Usage
Just keep using your deprecated block helpers, they can be converted once the transition to rails 3 is complete.

<% form_for xxx do |f| %>
  still works
<% end %>

Code

  # make <% helper do %> work
  block_concat = [
    [ActionView::Helpers::FormHelper, :fields_for],
    [ActionView::Helpers::FormBuilder, :fields_for],
    [ActionView::Helpers::FormHelper, :form_for],
    [ActionView::Helpers::FormTagHelper, :form_tag],
    [ActionView::Helpers::TagHelper, :content_tag],
    [ActionView::Helpers::UrlHelper, :link_to],
    [ActionView::Helpers::JavaScriptHelper, :javascript_tag],
    [ActionView::Helpers::CacheHelper, :cache],
  ]

  ERB_EXTENSION = '.erb'.freeze

  block_concat.each do |klass, method|
    klass.class_eval do
      without = "#{method}_without_concat".to_sym
      alias_method without, method
      define_method(method) do |*args, &block|
        result = send(without, *args, &block)
        if block && block.source_location.first.include?(ERB_EXTENSION) # called from a erb template ?
          (@template || self).concat(result) # deprecated erb concat helper
          ""
        else
          result
        end
      end
    end
  end