Make the temporary directory path contain uid of the process

[hanazuki]

This patch resolves #376 a problem with multi-user environment.

On many traditional *nix systems all the users on the same machine share a single global /tmp.
If two users on such a system run spring at the same time, the first user's spring process
creates /tmp/spring and stores a pidfile and a socket within the directory.
The second users process will then try to store its pidfile within /tmp/spring, but it fails
since the directory is owned by another user and (usually) not writable to non-owners.

This patch resolves this problem by making the temporary directory path used by spring
contain the UID of the running process.
If you are the user with UID of 1000, your spring processes will create the directory
$TMPDIR/spring-1000 and store everything therein.

---

Two other solutions are suggested on the issue #376

1. Use tmp directory inside the Rails application's tree
2. Make /tmp/spring world-writable

I think both of them have some problem

• As pointed out in the issue, Rails tmp may reside within a filesystem without domain socket support.
• Making /tmp/spring is not safe --- Let other users delete your socket.

AFAIK, Emacs and tmux takes this solution with process's UID to store per-user server socket in the global /tmp directory.

[rails-bot]

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[grosser]

that means atm you cannot run 2 springs at them same time either ? -> should we add the File.dirname(Rails.root) too ?

[grosser]

ahh ... all the others add application_id to the path ...
I'd say 👍 ... but better have @rafaelfranca + @jonleighton take another look ...

[jonleighton]

👍 from me.

[grosser]

@hanazuki can you rebase ?

[hanazuki]

@grosser Sure, I will.

[hanazuki]

Rebased on the current master

[grosser]

1.5.0 is out!

[hanazuki]

Thanks a lot!