threads / discuss / 34611
Subject: About close() in commit_lock_file()
Duy Nguyenclose() 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? Should we enclose close() in #ifdef __MINGW32__ (and maybe __CYGWIN__)? -- Duy
Junio C HamanoRe: About close() in commit_lock_file()
Duy Nguyen <pclouds@gmail.com> writes:
> 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?
Interesting.
> Should we enclose close() in #ifdef __MINGW32__ (and maybe > __CYGWIN__)?
Or just have "close and retry" code after seeing rename() fails with some known errno, without singling out a particular platform?
Johannes SixtRe: About close() in commit_lock_file()
Am 8/5/2013 16:23, schrieb Duy Nguyen:
> 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
Duy NguyenRe: About close() in commit_lock_file()
On Tue, Aug 6, 2013 at 1:41 PM, Johannes Sixt <j.sixt@viscovery.net> wrote:
> Am 8/5/2013 16:23, schrieb Duy Nguyen: >> 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.
The second process could unlink(.lock file) first, then open it, even using lock_file(), but I think that falls into your "first" and is an invalid case from git point of view, so..
> Conclusion: There is no problem.
Agreed. False alarm.
-- Duy