Commit eebc7caa authored by Jacob Kaplan-Moss's avatar Jacob Kaplan-Moss
Browse files

Fixed #8616 (again): prevent a race condition in the session file backend.... 

Fixed #8616 (again): prevent a race condition in the session file backend. Many thanks to Warren Smith for help and the eventual fix.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@8750 bcc190cf-cafb-0310-a4f2-bffc1f526a37
parent 1729d92f

AUTHORS

+1 −0
Original line number Diff line number Diff line
@@ -368,6 +368,7 @@ answer newbie questions, and generally made Django that much better: 
    Ben Slavin <benjamin.slavin@gmail.com>

    sloonz <simon.lipp@insa-lyon.fr>

    SmileyChris <smileychris@gmail.com>

    Warren Smith <warren@wandrsmith.net> 

    smurf@smurf.noris.de

    Vsevolod Solovyov

    sopel

django/contrib/sessions/backends/file.py

+55 −15
Original line number Diff line number Diff line
@@ -47,8 +47,12 @@ class SessionStore(SessionBase): 
        try:

            session_file = open(self._key_to_file(), "rb")

            try:

                file_data = session_file.read()

                # Don't fail if there is no data in the session file.

                # We may have opened the empty placeholder file.

                if file_data:

                    try:

                    session_data = self.decode(session_file.read())

                        session_data = self.decode(file_data)

                    except (EOFError, SuspiciousOperation):

                        self.create()

            finally:
@@ -69,23 +73,59 @@ class SessionStore(SessionBase): 
            return



    def save(self, must_create=False):

        flags = os.O_WRONLY | os.O_CREAT | os.O_TRUNC | getattr(os, 'O_BINARY', 0)

        if must_create:

            flags |= os.O_EXCL

        # Because this may trigger a load from storage, we must do it before

        # truncating the file to save.

        # Get the session data now, before we start messing

        # with the file it is stored within.

        session_data = self._get_session(no_load=must_create)



        session_file_name = self._key_to_file()



        try:

            fd = os.open(self._key_to_file(self.session_key), flags)

            try:

                os.write(fd, self.encode(session_data))

            finally:

            # Make sure the file exists.  If it does not already exist, an

            # empty placeholder file is created.

            flags = os.O_WRONLY | os.O_CREAT | getattr(os, 'O_BINARY', 0)

            if must_create:

                flags |= os.O_EXCL

            fd = os.open(session_file_name, flags)

            os.close(fd)



        except OSError, e:

            if must_create and e.errno == errno.EEXIST:

                raise CreateError

            raise

        except (IOError, EOFError):



        # Write the session file without interfering with other threads

        # or processes.  By writing to an atomically generated temporary

        # file and then using the atomic os.rename() to make the complete

        # file visible, we avoid having to lock the session file, while

        # still maintaining its integrity.

        #

        # Note: Locking the session file was explored, but rejected in part

        # because in order to be atomic and cross-platform, it required a

        # long-lived lock file for each session, doubling the number of

        # files in the session storage directory at any given time.  This

        # rename solution is cleaner and avoids any additional overhead

        # when reading the session data, which is the more common case

        # unless SESSION_SAVE_EVERY_REQUEST = True.

        #

        # See ticket #8616.

        dir, prefix = os.path.split(session_file_name)



        try:

            output_file_fd, output_file_name = tempfile.mkstemp(dir=dir,

                prefix=prefix + '_out_')

            try:

                try:

                    os.write(output_file_fd, self.encode(session_data))

                finally:

                    os.close(output_file_fd)

                renamed = False

                os.rename(output_file_name, session_file_name)

                renamed = True

            finally:

                if not renamed:

                    os.unlink(output_file_name)



        except (OSError, IOError, EOFError):

            pass



    def exists(self, session_key):