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# lock.py
# DNF Locking Subsystem.
#
# Copyright (C) 2013-2016 Red Hat, Inc.
#
# This copyrighted material is made available to anyone wishing to use,
# modify, copy, or redistribute it subject to the terms and conditions of
# the GNU General Public License v.2, or (at your option) any later version.
# This program is distributed in the hope that it will be useful, but WITHOUT
# ANY WARRANTY expressed or implied, including the implied warranties 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., 51 Franklin Street, Fifth Floor, Boston, MA
# 02110-1301, USA. Any Red Hat trademarks that are incorporated in the
# source code or documentation are not subject to the GNU General Public
# License and may only be used or replicated with the express permission of
# Red Hat, Inc.
#
from __future__ import absolute_import
from __future__ import unicode_literals
from dnf.exceptions import ProcessLockError, ThreadLockError, LockError
from dnf.i18n import _
from dnf.yum import misc
import dnf.logging
import dnf.util
import errno
import hashlib
import logging
import os
import threading
import time
logger = logging.getLogger("dnf")
def _fit_lock_dir(dir_):
if not dnf.util.am_i_root():
# for regular users the best we currently do is not to clash with
# another DNF process of the same user. Since dir_ is quite definitely
# not writable for us, yet significant, use its hash:
hexdir = hashlib.md5(dir_.encode('utf-8')).hexdigest()
dir_ = os.path.join(misc.getCacheDir(), 'locks', hexdir)
return dir_
def build_download_lock(cachedir, exit_on_lock):
return ProcessLock(os.path.join(_fit_lock_dir(cachedir), 'download_lock.pid'),
'cachedir', not exit_on_lock)
def build_metadata_lock(cachedir, exit_on_lock):
return ProcessLock(os.path.join(_fit_lock_dir(cachedir), 'metadata_lock.pid'),
'metadata', not exit_on_lock)
def build_rpmdb_lock(persistdir, exit_on_lock):
return ProcessLock(os.path.join(_fit_lock_dir(persistdir), 'rpmdb_lock.pid'),
'RPMDB', not exit_on_lock)
class ProcessLock(object):
def __init__(self, target, description, blocking=False):
self.blocking = blocking
self.count = 0
self.description = description
self.target = target
self.thread_lock = threading.RLock()
def _lock_thread(self):
if not self.thread_lock.acquire(blocking=False):
msg = '%s already locked by a different thread' % self.description
raise ThreadLockError(msg)
self.count += 1
def _try_lock(self):
pid = str(os.getpid()).encode('utf-8')
try:
fd = os.open(self.target, os.O_CREAT | os.O_WRONLY | os.O_EXCL, 0o644)
os.write(fd, pid)
os.close(fd)
return True
except OSError as e:
if e.errno == errno.EEXIST: # File exists
return False
raise
def _try_read_lock(self):
try:
with open(self.target, 'r') as f:
return int(f.readline())
except IOError:
return -1
except ValueError:
time.sleep(2)
try:
with open(self.target, 'r') as f:
return int(f.readline())
except IOError:
return -1
except ValueError:
msg = _('Malformed lock file found: %s.\n'
'Ensure no other dnf process is running and '
'remove the lock file manually or run '
'systemd-tmpfiles --remove dnf.conf.' % (self.target))
raise LockError(msg)
def _try_unlink(self):
try:
os.unlink(self.target)
return True
except OSError:
return False
def _unlock_thread(self):
self.count -= 1
self.thread_lock.release()
def __enter__(self):
dnf.util.ensure_dir(os.path.dirname(self.target))
self._lock_thread()
inform = True
prev_pid = 0
while not self._try_lock():
pid = self._try_read_lock()
if pid == -1:
# already removed by other process
continue
if pid == os.getpid():
# already locked by this process
return
if not os.access('/proc/%d/stat' % pid, os.F_OK):
# locked by a dead process
self._try_unlink()
continue
if not self.blocking:
self._unlock_thread()
msg = '%s already locked by %d' % (self.description, pid)
raise ProcessLockError(msg, pid)
if inform or prev_pid != pid:
msg = _('Waiting for process with pid %d to finish.' % (pid))
logger.info(msg)
inform = False
prev_pid = pid
time.sleep(2)
def __exit__(self, *exc_args):
if self.count == 1:
os.unlink(self.target)
self._unlock_thread()