ruby_tempfile_test.rb

# You will need Ruby on a Windows machine. Plus the ffi library.
require 'ffi'

class File::Temp
  extend FFI::Library

  ffi_lib :kernel32

  attach_function :GetTempFileNameA, %i[string string uint buffer_out], :uint
  attach_function :GetTempFileNameW, %i[buffer_in buffer_in uint buffer_out], :uint

  def tmpfile_a
    # Update as needed
    file_name = "C:\\Users\\DANIEL~1\\AppData\\Local\\Temp"

    buf = 0.chr * 1024
    prefix = 'rb_'

    if GetTempFileNameA(file_name, prefix, 0, buf) == 0
      raise SystemCallError, FFI.errno, 'GetTempFileNameW'
    end

    file_name = buf.strip
  end

  def tmpfile_w
    # Update as needed
    file_name = "C:\\Users\\DANIEL~1\\AppData\\Local\\Temp"

    buf = 0.chr * 1024
    buf.encode!('UTF-16LE')

    prefix = 'rb_'
    prefix.encode!('UTF-16LE')

    # I suspect "buf" is the culprit but I'm not sure what to do about it. But then
    # why doesn't it blow up in the "A" version? Hmm...
    if GetTempFileNameW(file_name, prefix, 0, buf) == 0
      raise SystemCallError, FFI.errno, 'GetTempFileNameW'
    end

    file_name = buf.strip
  end
end

puts "Starting A version" # This works

threads_a = []
20.times{ threads_a << Thread.new{ p File::Temp.new.tmpfile_a } }
threads_a.each(&:join)

puts "Done with A version"

puts "Starting W version" # This blows up

threads_a = []
20.times{ threads_a << Thread.new{ p File::Temp.new.tmpfile_w } }
threads_a.each(&:join)

puts "Done with W version"