Feature #20497: Tempfile.create_io

• Status: Closed
• Assignee: -
• Target version: -

[akr (Akira Tanaka)]

I propose Tempfile.create_io.
It is similar to Tempfile.create but the actual file is unlinked before returning the method.

https://github.com/ruby/ruby/pull/10803

Purpose:

Sometimes, applications need a temporary file but it is not required to access via a pathname.
In this case, the created file can be unlinked just after temporary file creation.
This removes the obligation of removing the file from applications.
So, Tempfile.create_io is easier to use than Tempfile.create.

Example:

tmpio = Tempfile.create_io  # => #<IO:fd 5>
tmpio.class                 # => IO
tmpio.path                  # => nil
tmpio.stat.mode.to_s(8)     # => "100600"
tmpio.puts "foo"
tmpio.rewind
tmpio.read                  # => "foo\n"
tmpio.close

Portability:
This feature (unlink just after file creation) is supported on Unix for a long time.

Linux 3.11 has O_TMPFILE to create an unnamed file.
The current implementation uses it.

I heard that it is possible on Windows. (O_SHARE_DELETE?)
I'm not sure how to use it.

[matz (Yukihiro Matsumoto)]

From what I understand, the real intent of this proposal is to "let the OS clean up after the generated tempfile". If so, I don't think the name create_io represents the intent.
I vote for adding a keyword argument to Tempfile.create.

Matz.

[shyouhei (Shyouhei Urabe)]

Previous discussions:

• https://bugs.ruby-lang.org/issues/11715 @akr (Akira Tanaka) thinks it's a good idea to have an anonymous file, then name it afterwards.
• https://bugs.ruby-lang.org/issues/13743 @akr (Akira Tanaka) is against the pull request which actually adds such feature (maybe it was the implementation and the idea was OK though).

Because the proposed Tempfile.create_io returns a non-File IO instance, there is no way to assign a path in this ticket.

[akr (Akira Tanaka)]

matz (Yukihiro Matsumoto) wrote in #note-1:

From what I understand, the real intent of this proposal is to "let the OS clean up after the generated tempfile". If so, I don't think the name create_io represents the intent.
I vote for adding a keyword argument to Tempfile.create.

I updated the PR to change the interface:
I added unlink_first keyword argument for Tempfile.create.

f = Tempfile.create(unlink_first: true)
# The file is already removed because unlink_first
f.path                  # => "/tmp/"  (no filename since no file)
f.puts "foo"
f.rewind
f.read                  # => "foo\n"
f.close

Tempfile.create(unlink_first: true) {|f|
  # The file is already removed because unlink_first
  f.path                # => "/tmp/"  (no filename since no file)
  f.puts "foo"
  f.rewind
  f.read                # => "foo\n"
}

[akr (Akira Tanaka)]

Several candidates for the keyword argument:

• unlink_first: true

• remove_immediately: true

• delete_on_creation: true

• unnamed: true

• nameless: true

• anonymous: true

• named: false

[byroot (Jean Boussier)]

My personal preference would go to anonymous: true, probably followed by linked: false.

[austin (Austin Ziegler)]

I have a minor preference for unnamed: true, but anonymous: true is probably more approachable overall.

[akr (Akira Tanaka)]

I talked with Matz today.
He said anonymous: true is acceptable.

[akr (Akira Tanaka)]

• Status changed from Open to Closed

Applied in changeset git|3ee83c73c38070d695537d4322ce4decb970a54a.

---

Tempfile.create(anonymous: true) implemented. (#10803)

The keyword argument anonymous is implemented for Tempfile.create

The default is anonymous: false.
The behavior is not changed as before.

The created temporary file is immediately removed if anonymous: true is specified.
So applications don't need to remove the file.
The actual storage of the file is reclaimed by the OS when the file is closed.

It uses O_TMPFILE for Linux 3.11 or later.
It creates an anonymous file from the beginning.

It uses FILE_SHARE_DELETE for Windows.
It makes it possible to remove the opened file.

[Feature #20497]