~bzr-pqm/bzr/bzr.dev

# Copyright (C) 2007 Canonical Ltd

#

# This program is free software; you can redistribute it and/or modify

# it under the terms of the GNU General Public License as published by

# the Free Software Foundation; either version 2 of the License, or

# (at your option) any later version.

#

# This program is distributed in the hope that it will be useful,

# but WITHOUT ANY WARRANTY; without even the implied warranty of

# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

# GNU General Public License for more details.

#

# You should have received a copy of the GNU General Public License

# along with this program; if not, write to the Free Software

# Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA

"""Tests for temporarily upgrading to a WriteLock."""

from bzrlib import (

    errors,

    )

from bzrlib.tests.per_lock import TestCaseWithLock

class TestTemporaryWriteLock(TestCaseWithLock):

    def setUp(self):

        super(TestTemporaryWriteLock, self).setUp()

        self.build_tree(['a-file'])

    def test_can_upgrade_and_write(self):

        """With only one lock, we should be able to write lock and switch back."""

        a_lock = self.read_lock('a-file')

        try:

            success, t_write_lock = a_lock.temporary_write_lock()

            self.assertTrue(success, "We failed to grab a write lock.")

            try:

                self.assertEqual('contents of a-file\n',

                                 t_write_lock.f.read())

                # We should be able to write to the file.

                t_write_lock.f.seek(0)

                t_write_lock.f.write('new contents for a-file\n')

                t_write_lock.f.seek(0)

                self.assertEqual('new contents for a-file\n',

                                 t_write_lock.f.read())

            finally:

                a_lock = t_write_lock.restore_read_lock()

        finally:

            a_lock.unlock()

    def test_is_write_locked(self):

        """With a temporary write lock, we cannot grab another lock."""

        a_lock = self.read_lock('a-file')

        try:

            success, t_write_lock = a_lock.temporary_write_lock()

            self.assertTrue(success, "We failed to grab a write lock.")

            try:

                self.assertRaises(errors.LockContention,

                                  self.write_lock, 'a-file')

                # TODO: jam 20070319 fcntl read locks are not currently fully

                #       mutually exclusive with write locks. This will be fixed

                #       in the next release.

                # self.assertRaises(errors.LockContention,

                #                   self.read_lock, 'a-file')

            finally:

                a_lock = t_write_lock.restore_read_lock()

            # Now we only have a read lock, so we should be able to grab

            # another read lock, but not a write lock

            # TODO: jam 20070319 fcntl write locks are not currently fully

            #       mutually exclusive with read locks. This will be fixed

            #       in the next release.

            # self.assertRaises(errors.LockContention,

            #                   self.write_lock, 'a-file')

            b_lock = self.read_lock('a-file')

            b_lock.unlock()

        finally:

            a_lock.unlock()

    def test_fails_when_locked(self):

        """We can't upgrade to a write lock if something else locks."""

        a_lock = self.read_lock('a-file')

        try:

            b_lock = self.read_lock('a-file')

            try:

                success, alt_lock = a_lock.temporary_write_lock()

                self.assertFalse(success)

                # Now, 'alt_lock' should be a read-lock on the file. It should

                # either be the same object as a_lock, or a new object.

                # If it is a new object, a_lock should be unlocked. (we don't

                # want to end up with 2 locks on the file)

                self.assertTrue((alt_lock is a_lock) or (a_lock.f is None))

                # set a_lock = alt_lock so that cleanup works correctly

                a_lock = alt_lock

                # We should not be able to grab a write lock

                # but we should be able to grab another read lock

                # TODO: jam 20070319 fcntl write locks are not currently fully

                #       mutually exclusive with read locks. This will be fixed

                #       in the next release.

                # self.assertRaises(errors.LockContention,

                #                   self.write_lock, 'a-file')

                c_lock = self.read_lock('a-file')

                c_lock.unlock()

            finally:

                b_lock.unlock()

        finally:

            a_lock.unlock()

    # TODO: jam 20070314 to truly test these, we should be spawning an external

    #       process, and having it lock/unlock/try lock on request.

    # TODO: jam 20070314 Test that the write lock can fail if another process

    #       holds a read lock. And that we recover properly.