Method: IO.fast_select

Defined in:
lib/openc3/core_ext/io.rb

.fast_select(read_sockets = nil, write_sockets = nil, error_array = nil, timeout = nil) ⇒ Object

On Windows the IO.select function (when called with no timeout) takes a minimum of 10 msec to return, even if one of the IO objects is ready to read/write sooner than that.

This method is identical to IO.select but instead of calling IO.select with the full timeout, it calls IO.select with a small timeout and then doubles the timeout twice until eventually it calls IO.select with the remaining passed in timeout value.

Parameters:

  • read_sockets (Array<IO>) (defaults to: nil) —

    IO objects to wait to be ready to read

  • write_sockets (Array<IO>) (defaults to: nil) —

    IO objects to wait to be ready to write

  • error_array (Array<IO>) (defaults to: nil) —

    IO objects to wait for exceptions

  • timeout (Numeric) (defaults to: nil) —

    Number of seconds to wait



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# File 'lib/openc3/core_ext/io.rb', line 53

def fast_select(read_sockets = nil, write_sockets = nil, error_array = nil, timeout = nil)
  # Always try a zero timeout first
  current_timeout = SELECT_BASE_TIMEOUT
  total_timeout = 0.0

  while true
    begin
      result = IO.__select__(read_sockets, write_sockets, error_array, current_timeout)
    # All OS errors are subclassed to SystemCallError as Errno::<Subclass>
    # See https://ruby-doc.org/core-3.1.0/Errno.html
    rescue SystemCallError
      return nil
    end
    return result if result or current_timeout.nil?
    return nil if timeout and total_timeout >= timeout

    if current_timeout <= 0.0001
      # Always try the base timeout next
      current_timeout = SELECT_BASE_TIMEOUT
      total_timeout = SELECT_BASE_TIMEOUT
    else
      # Then start doubling the timeout
      current_timeout = current_timeout * 2

      # Until it is bigger than our max timeout
      if current_timeout >= SELECT_MAX_TIMEOUT
        if timeout
          # Block for the remaining requested timeout
          current_timeout = timeout - total_timeout
          total_timeout = timeout
        else
          # Or block forever
          current_timeout = nil
        end
      else
        # Or it is bigger than the given timeout
        if timeout and current_timeout >= timeout
          # Block for the remaining requested timeout
          current_timeout = timeout - total_timeout
          total_timeout = timeout
        else
          # Up our total time in select
          total_timeout += current_timeout
        end
        if timeout and total_timeout > timeout
          # Block for the remaining requested timeout
          current_timeout = timeout - total_timeout
          total_timeout = timeout
        end
      end
      return nil if current_timeout and current_timeout < 0
    end
  end # while true
end