blob: 755d68cb5842071f8036f5c4a85ea086b46a4d13 [file] [log] [blame]
# Copyright (c) 2012 The Chromium OS Authors. All rights reserved.
# Use of this source code is governed by a BSD-style license that can be
# found in the LICENSE file.
import os
import signal
import sys
from chromite.lib import cros_build_lib
from chromite.lib import locking
class EnforcedCleanupSection(object):
"""Context manager used to ensure that a section of cleanup code is run
This is designed such that a child splits off, ensuring that even if the
parent is sigkilled, the section marked *will* be run. This is implemented
via a ProcessLock shared between parent, and a process split off to
survive any sigkills/hard crashes in the parent.
The usage of this is basically in a pseudo-transactional manner:
>>> with EnforcedCleanupSection() as critical:
... with other_handler:
... try:
... critical.ForkWatchdog()
... # Everything past here doesn't run during enforced cleanup
... # ... normal code
... finally:
... pass # This is guaranteed to run.
... # The __exit__ for other_handler is guaranteed to run.
... # Anything from this point forward will only be run by the invoking
... # process. If cleanup enforcement had to occur, any code from this
... # point forward won't be run.
def __init__(self):
self._lock = locking.ProcessLock(verbose=False)
self._forked = False
self._is_child = False
def ForkWatchdog(self):
if self._forked:
raise RuntimeError("MarkCleanup was invoked twice for %s" % (self,))
self._forked = True
child_pid = os.fork()
if child_pid:
# Parent.
# Since we share stdin/stdout/whatever, suppress sigint should we somehow
# become the foreground process in the session group.
signal.signal(signal.SIGINT, signal.SIG_IGN)
# Child code. We lose the lock via lockf/fork semantics.
self._is_child = True
except Exception, e:
print >>sys.stderr, ("EnforcedCleanupSection %s excepted(%r) attempting "
"to take the write lock; hard exiting." % (self, e))
# We have no way of knowing the state of the parent if this locking
# fails- failure means a code bug. Specifically, we don't know if
# cleanup code was run, thus just flat out bail.
# Check if the parent exited cleanly; if so, we don't need to do anything.
if, 1):
# Allow masterpid context managers to run in this case, since we're
# explicitly designed for this cleanup.
cros_build_lib.MasterPidContextManager._ALTERNATE_MASTER_PID = os.getpid()
raise RuntimeError("Parent exited uncleanly; forcing cleanup code to run.")
def __enter__(self):
return self
def __exit__(self, exc, exc_type, tb):
if self._is_child:
# All cleanup code that would've run, has ran.
# Hard exit to bypass any further code execution.
os.write(self._lock.fd, '\n')