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Bug #15633

closed

Pathological slowdown in File.expand_path on UNC paths on Windows

Added by djberg96 (Daniel Berger) over 5 years ago. Updated over 5 years ago.

Status:
Closed
Assignee:
-
Target version:
-
ruby -v:
ruby 2.5.1p57 (2018-03-29 revision 63029) [x64-mingw32]
Backport:
2.4: UNKNOWN, 2.5: UNKNOWN, 2.6: UNKNOWN
[ruby-core:91656]

Description

For a while now, including Ruby 2.5, calling File.expand_path on an absolute UNC path seems to be strangely slow. I've put together some benchmarks here:

require 'benchmark'

MAX = 200000

Benchmark.bm(30) do |x|
  x.report("expand_path('foo/bar')") do
    str = "foo/bar"
    MAX.times{ File.expand_path(str) }
  end

  x.report("expand_path('C:/foo/bar')") do
    str = "C:/foo/bar"
    MAX.times{ File.expand_path(str) }
  end

  x.report("expand_path('//foo/bar')") do
    str = "//foo/bar"
    MAX.times{ File.expand_path(str) }
  end

  x.report("expand_path('foo//bar///')") do
    str = "foo//bar///"
    MAX.times{ File.expand_path(str) }
  end

  x.report("expand_path('~')") do
    str = "~"
    MAX.times{ File.expand_path(str) }
  end

  x.report("expand_path('')") do
    str = ""
    MAX.times{ File.expand_path(str) }
  end

  x.report("expand_path('', '~')") do
    MAX.times{ File.expand_path('', '~') }
  end
end

What I see is that most of these take only a second or two, while the UNC path takes 30+ seconds.

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