Issue #13276 has been updated by nobu (Nobuyoshi Nakada).

Status changed from Open to Assigned
Assignee set to nobu (Nobuyoshi Nakada)

This bug predates 1.0, so it will be fixed by 2.5 but won't be backported.

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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-63663

* Author: floehopper (James Mead)
* Status: Assigned
* Priority: Normal
* Assignee: nobu (Nobuyoshi Nakada)
* 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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