[ruby-core:79924] [Ruby trunk Bug#13276] Dir.glob returns empty array when OS has no more file handles (expected exception)

Issue #13276 has been updated by James Mead.

Description updated

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Bug #13276: Dir.glob returns empty array when OS has no more file handles (expected exception)
https://bugs.ruby-lang.org/issues/13276#change-63354

* Author: James Mead
* Status: Open
* Priority: Normal
* Assignee: 
* Target version: 
* ruby -v: ruby 2.3.1p112 (2016-04-26 revision 54768) [x86_64-darwin14]
* Backport: 2.2: UNKNOWN, 2.3: UNKNOWN, 2.4: UNKNOWN
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The following terminal session demonstrates how `Dir.glob` returns an empty array when the OS has run out of file handles; whereas `File.new` raises a `Errno::EMFILE` exception.

I would expect `Dir.glob` to fail fast in a similar way to `File.new`.

~~~
$ mkdir /tmp/ruby-dir-glob-returns-empty-array-when-too-many-open-files
$ cd /tmp/ruby-dir-glob-returns-empty-array-when-too-many-open-files
$ touch foo
$ ulimit -n 16
$ ruby -e "1.upto(16).map { |i| p [i, Dir.glob('*')]; File.new('foo') }"
[1, ["foo"]]
[2, ["foo"]]
[3, ["foo"]]
[4, ["foo"]]
[5, ["foo"]]
[6, ["foo"]]
[7, ["foo"]]
[8, ["foo"]]
[9, ["foo"]]
[10, []] # Dir.glob returns empty array and does not raise exception
-e:1:in `initialize': Too many open files @ rb_sysopen - foo (Errno::EMFILE)
	from -e:1:in `new'
	from -e:1:in `block in <main>'
	from -e:1:in `upto'
	from -e:1:in `each'
	from -e:1:in `map'
	from -e:1:in `<main>'
~~~

The following is a counter example which shows how `Dir.new` raises an exception under the same conditions.

~~~
$ mkdir /tmp/ruby-dir-new-raises-exception-when-too-many-files-open
$ cd /tmp/ruby-dir-new-raises-exception-when-too-many-files-open
$ touch foo
$ mkdir bar
$ ulimit -n 16
$ ruby -e "1.upto(16).map { |i| p [i, Dir.new('bar')]; File.new('foo') }"
[1, #<Dir:bar>]
[2, #<Dir:bar>]
[3, #<Dir:bar>]
[4, #<Dir:bar>]
[5, #<Dir:bar>]
[6, #<Dir:bar>]
[7, #<Dir:bar>]
[8, #<Dir:bar>]
[9, #<Dir:bar>]
-e:1:in `initialize': Too many open files @ dir_initialize - bar (Errno::EMFILE)
	from -e:1:in `new'
	from -e:1:in `block in <main>'
	from -e:1:in `upto'
	from -e:1:in `each'
	from -e:1:in `map'
	from -e:1:in `<main>'
~~~

This is what I would expect for `Dir.glob`, i.e. I would expect an exception like this: `Too many open files @ dir_s_glob (Errno::EMFILE)` in the first example.




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