Class: ExternalSortModule::ChunkReader

Inherits:
Chunk
  • Object
show all
Defined in:
lib/geotree/externalsort.rb

Overview

Chunk subclass that performs streaming reading of target with sliding window

Instance Method Summary collapse

Methods inherited from Chunk

#done, #set_chunk_size

Constructor Details

#initialize(target_file, target_offset, target_length, element_size, chunk_size = MAX_CHUNK_SIZE_) ⇒ ChunkReader

Returns a new instance of ChunkReader.



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# File 'lib/geotree/externalsort.rb', line 98

def initialize(target_file, target_offset, target_length, element_size, chunk_size = MAX_CHUNK_SIZE_)
  super(target_file,target_offset,target_length,element_size, chunk_size)
end

Instance Method Details

#peek ⇒ array, offset

Get next element

Returns:

  • (array, offset) —

    containing element, or nil if chunk is done



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# File 'lib/geotree/externalsort.rb', line 112

def peek
  nil if done

  # If no more elements exist in the buffer, fill it from the target
  if @buffer_offset == @buffer.size
    max_size = @max_chunk_size

    chunk_size = [@target_end_offset - @target_offset, max_size].min

    f = @target_file
    f.pos = @target_offset
    @buffer = f.read(chunk_size)
    raise IOError if !@buffer || @buffer.size != chunk_size

    @target_offset += chunk_size
    @buffer_offset = 0
  end
  [@buffer, @buffer_offset]
end

#peek_dump ⇒ Object

Display record being viewed using hex dump



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# File 'lib/geotree/externalsort.rb', line 103

def peek_dump
  "(done)" if done

  buff, off = peek
  "Next element: "+hex_dump_to_string(buff,nil,off,@element_size)
end

#read ⇒ array, offset

Read next element, advance pointers

Returns:

  • (array, offset) —

    containing element

Raises:

  • IllegalStateException if already done



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# File 'lib/geotree/externalsort.rb', line 135

def read
  ret = peek
  raise IllegalStateException if !ret
  @buffer_offset += @element_size
  ret
end