114 lines
2.2 KiB
Crystal
114 lines
2.2 KiB
Crystal
require "file_utils"
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require "json"
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class Hash(K,V)
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def reverse
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rev = Array(Tuple(K,V)).new
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keys = Array(K).new
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each_key do |k|
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keys << k
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end
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keys.reverse.each do |k|
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rev << {k, self.[k]}
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end
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rev
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end
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end
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class DODB::CachedDataBase(V) < DODB::Storage(V)
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@indexers = [] of Indexer(V)
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property data = Hash(Int32, V).new
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def initialize(@directory_name : String)
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Dir.mkdir_p data_path
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Dir.mkdir_p locks_directory
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begin
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self.last_index
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rescue
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self.last_index = -1
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end
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# TODO: load the database in RAM at start-up
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DODB::DataBase(V).new(@directory_name).each_with_index do |v, index|
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puts "loading value #{v} at index #{index}"
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self[index] = v
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end
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end
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# Getting data from the hash in RAM.
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def []?(key : Int32) : V?
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@data[key]
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rescue e
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# FIXME: rescues any error the same way.
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return nil
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end
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def [](key : Int32) : V
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# raise MissingEntry.new(key) unless ::File.exists? file_path key
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# read file_path key
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@data[key] rescue raise MissingEntry.new(key)
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end
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def []=(index : Int32, value : V)
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old_value = self.[index]?
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check_collisions! index, value, old_value
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# Removes any old indices or partitions pointing to a value about
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# to be replaced.
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if old_value
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remove_partitions index, old_value
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end
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# Avoids corruption in case the application crashes while writing.
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file_path(index).tap do |path|
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::File.write "#{path}.new", value.to_json
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::FileUtils.mv "#{path}.new", path
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end
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write_partitions index, value
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if index > last_index
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self.last_index = index
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end
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@data[index] = value
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end
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##
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# Can be useful for making dumps or to restore a database.
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def each_with_index(reversed : Bool = false, start_offset = 0, end_offset : Int32? = nil)
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i = -1 # do not trust key to be the right index
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(reversed ? @data.reverse : @data).each do |index, v|
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i += 1
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next if start_offset > i
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break unless end_offset.nil? || i <= end_offset
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yield v, index
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end
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end
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def delete(key : Int32)
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value = self[key]?
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return if value.nil?
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begin
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::File.delete file_path key
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rescue
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# FIXME: Only intercept “no such file" errors
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end
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remove_partitions key, value
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@data.delete key
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value
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end
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private def remove_data!
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super
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@data = Hash(Int32, V).new
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end
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end
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