Class: Codnar::Cache

Inherits:
Object
  • Object
show all
Defined in:
lib/codnar/cache.rb

Overview

Cache long computations in disk files.

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(directory, &block) ⇒ Cache

Connect to an existing disk cache. The cache is expected to be stored in a directory of the specified name, which is either in the current working directory or in one of its parent directories.



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# File 'lib/codnar/cache.rb', line 12

def initialize(directory, &block)
  @force_recompute = false
  @computation = block
  @directory = find_directory(Dir.pwd, directory)
  if @directory
    class <<self; alias [] :cached_computation; end
  else
    class <<self; alias [] :uncached_computation; end
    $stderr.puts("#{$0}: Could not find cache directory: #{directory}.")
  end
end

Instance Attribute Details

#force_recompute ⇒ Object

Whether to recompute values even if they are cached.



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# File 'lib/codnar/cache.rb', line 7

def force_recompute
  @force_recompute
end

Instance Method Details

#cache_file(input) ⇒ Object

Return the file expected to cache the computed results for a given input,



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# File 'lib/codnar/cache.rb', line 36

def cache_file(input)
  key = Digest.hexencode(Digest::SHA2.digest(input.to_yaml))
  return @directory + "/" + key + ".yaml"
end

#cached_computation(input) ⇒ Object

Access the results of the computation for the specified input. Fetch the result from the cache if it is there, otherwise invoke the computation and store the result in the cache for the next time.



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# File 'lib/codnar/cache.rb', line 27

def cached_computation(input)
  file = cache_file(input)
  return YAML.load_file(file) if File.exists?(file) and not @force_recompute
  result = @computation.call(input)
  File.open(file, "w") { |file| file.write(result.to_yaml) }
  return result
end

#uncached_computation(input) ⇒ Object

Access the results of a computation for the specified input, in case we do not have a cache directory to look for and store the results in.



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# File 'lib/codnar/cache.rb', line 43

def uncached_computation(input)
  return @computation.call(input)
end