Re: About close() in commit_lock_file()

From: Johannes Sixt <j.sixt@viscovery.net>
Date: Aug 6, 2013, 06:41 UTC
Message-ID: <52009A90.7050701@viscovery.net>
In-Reply-To: <CACsJy8By1cpPZ5QyVd6VhKSkd-y_E6pTYdDimK9P0wXia-uMqg@mail.gmail.com>

Am 8/5/2013 16:23, schrieb Duy Nguyen:

Show 5 quoted lines

> close() is added in commit_lock_file(), before rename(), by 4723ee9
> (Close files opened by lock_file() before unlinking. - 2007-11-13),
> which is needed by Windows. But doesn't that create a gap between
> close() and rename() on other platforms where another process can
> replace .lock file with something else before rename() is executed?

First, files manipulated by commit_lock_file() are to be opened only using lock_file() by definition. Opening such a file in with open() or fopen() or renaming it via rename() without using the lockfile.[ch] API is possible regardless of whether commit_lock_file() has closed the file or not. Such manipulation is already undefined behavior (from Git's point of view), and there is nothing we can do about "misbehaving" processes.

Second, lock_file() uses O_CREAT|O_EXCL, which fails when the file exists, regardless of whether it is open or not.

Conclusion: There is no problem.

-- Hannes