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This builds on https://github.com/python/cpython/pull/106807, which adds a return code to ResourceTracker, to make future debugging easier. Testing this “in situ” proved difficult, since the global ResourceTracker is involved in test infrastructure. So, the tests here create a new instance and feed it fake data. --------- Co-authored-by: Yonatan Bitton <yonatan.bitton@perception-point.io> Co-authored-by: Yonatan Bitton <bityob@gmail.com> Co-authored-by: Antoine Pitrou <antoine@python.org>
296 lines
11 KiB
Python
296 lines
11 KiB
Python
###############################################################################
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# Server process to keep track of unlinked resources (like shared memory
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# segments, semaphores etc.) and clean them.
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#
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# On Unix we run a server process which keeps track of unlinked
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# resources. The server ignores SIGINT and SIGTERM and reads from a
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# pipe. Every other process of the program has a copy of the writable
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# end of the pipe, so we get EOF when all other processes have exited.
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# Then the server process unlinks any remaining resource names.
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#
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# This is important because there may be system limits for such resources: for
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# instance, the system only supports a limited number of named semaphores, and
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# shared-memory segments live in the RAM. If a python process leaks such a
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# resource, this resource will not be removed till the next reboot. Without
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# this resource tracker process, "killall python" would probably leave unlinked
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# resources.
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import os
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import signal
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import sys
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import threading
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import warnings
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from . import spawn
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from . import util
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__all__ = ['ensure_running', 'register', 'unregister']
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_HAVE_SIGMASK = hasattr(signal, 'pthread_sigmask')
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_IGNORED_SIGNALS = (signal.SIGINT, signal.SIGTERM)
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def cleanup_noop(name):
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raise RuntimeError('noop should never be registered or cleaned up')
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_CLEANUP_FUNCS = {
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'noop': cleanup_noop,
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'dummy': lambda name: None, # Dummy resource used in tests
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}
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if os.name == 'posix':
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import _multiprocessing
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import _posixshmem
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# Use sem_unlink() to clean up named semaphores.
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#
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# sem_unlink() may be missing if the Python build process detected the
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# absence of POSIX named semaphores. In that case, no named semaphores were
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# ever opened, so no cleanup would be necessary.
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if hasattr(_multiprocessing, 'sem_unlink'):
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_CLEANUP_FUNCS.update({
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'semaphore': _multiprocessing.sem_unlink,
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})
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_CLEANUP_FUNCS.update({
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'shared_memory': _posixshmem.shm_unlink,
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})
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class ReentrantCallError(RuntimeError):
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pass
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class ResourceTracker(object):
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def __init__(self):
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self._lock = threading.RLock()
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self._fd = None
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self._pid = None
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self._exitcode = None
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def _reentrant_call_error(self):
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# gh-109629: this happens if an explicit call to the ResourceTracker
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# gets interrupted by a garbage collection, invoking a finalizer (*)
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# that itself calls back into ResourceTracker.
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# (*) for example the SemLock finalizer
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raise ReentrantCallError(
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"Reentrant call into the multiprocessing resource tracker")
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def _stop(self):
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with self._lock:
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# This should not happen (_stop() isn't called by a finalizer)
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# but we check for it anyway.
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if self._lock._recursion_count() > 1:
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return self._reentrant_call_error()
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if self._fd is None:
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# not running
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return
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# closing the "alive" file descriptor stops main()
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os.close(self._fd)
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self._fd = None
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_, status = os.waitpid(self._pid, 0)
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self._pid = None
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try:
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self._exitcode = os.waitstatus_to_exitcode(status)
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except ValueError:
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# os.waitstatus_to_exitcode may raise an exception for invalid values
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self._exitcode = None
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def getfd(self):
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self.ensure_running()
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return self._fd
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def ensure_running(self):
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'''Make sure that resource tracker process is running.
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This can be run from any process. Usually a child process will use
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the resource created by its parent.'''
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with self._lock:
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if self._lock._recursion_count() > 1:
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# The code below is certainly not reentrant-safe, so bail out
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return self._reentrant_call_error()
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if self._fd is not None:
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# resource tracker was launched before, is it still running?
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if self._check_alive():
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# => still alive
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return
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# => dead, launch it again
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os.close(self._fd)
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# Clean-up to avoid dangling processes.
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try:
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# _pid can be None if this process is a child from another
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# python process, which has started the resource_tracker.
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if self._pid is not None:
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os.waitpid(self._pid, 0)
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except ChildProcessError:
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# The resource_tracker has already been terminated.
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pass
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self._fd = None
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self._pid = None
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self._exitcode = None
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warnings.warn('resource_tracker: process died unexpectedly, '
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'relaunching. Some resources might leak.')
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fds_to_pass = []
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try:
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fds_to_pass.append(sys.stderr.fileno())
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except Exception:
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pass
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cmd = 'from multiprocessing.resource_tracker import main;main(%d)'
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r, w = os.pipe()
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try:
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fds_to_pass.append(r)
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# process will out live us, so no need to wait on pid
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exe = spawn.get_executable()
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args = [exe] + util._args_from_interpreter_flags()
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args += ['-c', cmd % r]
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# bpo-33613: Register a signal mask that will block the signals.
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# This signal mask will be inherited by the child that is going
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# to be spawned and will protect the child from a race condition
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# that can make the child die before it registers signal handlers
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# for SIGINT and SIGTERM. The mask is unregistered after spawning
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# the child.
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try:
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if _HAVE_SIGMASK:
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signal.pthread_sigmask(signal.SIG_BLOCK, _IGNORED_SIGNALS)
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pid = util.spawnv_passfds(exe, args, fds_to_pass)
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finally:
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if _HAVE_SIGMASK:
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signal.pthread_sigmask(signal.SIG_UNBLOCK, _IGNORED_SIGNALS)
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except:
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os.close(w)
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raise
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else:
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self._fd = w
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self._pid = pid
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finally:
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os.close(r)
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def _check_alive(self):
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'''Check that the pipe has not been closed by sending a probe.'''
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try:
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# We cannot use send here as it calls ensure_running, creating
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# a cycle.
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os.write(self._fd, b'PROBE:0:noop\n')
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except OSError:
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return False
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else:
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return True
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def register(self, name, rtype):
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'''Register name of resource with resource tracker.'''
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self._send('REGISTER', name, rtype)
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def unregister(self, name, rtype):
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'''Unregister name of resource with resource tracker.'''
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self._send('UNREGISTER', name, rtype)
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def _send(self, cmd, name, rtype):
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try:
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self.ensure_running()
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except ReentrantCallError:
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# The code below might or might not work, depending on whether
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# the resource tracker was already running and still alive.
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# Better warn the user.
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# (XXX is warnings.warn itself reentrant-safe? :-)
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warnings.warn(
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f"ResourceTracker called reentrantly for resource cleanup, "
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f"which is unsupported. "
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f"The {rtype} object {name!r} might leak.")
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msg = '{0}:{1}:{2}\n'.format(cmd, name, rtype).encode('ascii')
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if len(msg) > 512:
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# posix guarantees that writes to a pipe of less than PIPE_BUF
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# bytes are atomic, and that PIPE_BUF >= 512
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raise ValueError('msg too long')
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nbytes = os.write(self._fd, msg)
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assert nbytes == len(msg), "nbytes {0:n} but len(msg) {1:n}".format(
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nbytes, len(msg))
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_resource_tracker = ResourceTracker()
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ensure_running = _resource_tracker.ensure_running
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register = _resource_tracker.register
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unregister = _resource_tracker.unregister
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getfd = _resource_tracker.getfd
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def main(fd):
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'''Run resource tracker.'''
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# protect the process from ^C and "killall python" etc
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signal.signal(signal.SIGINT, signal.SIG_IGN)
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signal.signal(signal.SIGTERM, signal.SIG_IGN)
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if _HAVE_SIGMASK:
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signal.pthread_sigmask(signal.SIG_UNBLOCK, _IGNORED_SIGNALS)
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for f in (sys.stdin, sys.stdout):
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try:
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f.close()
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except Exception:
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pass
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cache = {rtype: set() for rtype in _CLEANUP_FUNCS.keys()}
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exit_code = 0
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try:
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# keep track of registered/unregistered resources
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with open(fd, 'rb') as f:
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for line in f:
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try:
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cmd, name, rtype = line.strip().decode('ascii').split(':')
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cleanup_func = _CLEANUP_FUNCS.get(rtype, None)
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if cleanup_func is None:
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raise ValueError(
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f'Cannot register {name} for automatic cleanup: '
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f'unknown resource type {rtype}')
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if cmd == 'REGISTER':
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cache[rtype].add(name)
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elif cmd == 'UNREGISTER':
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cache[rtype].remove(name)
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elif cmd == 'PROBE':
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pass
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else:
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raise RuntimeError('unrecognized command %r' % cmd)
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except Exception:
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exit_code = 3
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try:
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sys.excepthook(*sys.exc_info())
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except:
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pass
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finally:
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# all processes have terminated; cleanup any remaining resources
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for rtype, rtype_cache in cache.items():
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if rtype_cache:
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try:
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exit_code = 1
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if rtype == 'dummy':
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# The test 'dummy' resource is expected to leak.
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# We skip the warning (and *only* the warning) for it.
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pass
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else:
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warnings.warn(
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f'resource_tracker: There appear to be '
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f'{len(rtype_cache)} leaked {rtype} objects to '
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f'clean up at shutdown: {rtype_cache}'
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)
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except Exception:
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pass
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for name in rtype_cache:
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# For some reason the process which created and registered this
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# resource has failed to unregister it. Presumably it has
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# died. We therefore unlink it.
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try:
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try:
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_CLEANUP_FUNCS[rtype](name)
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except Exception as e:
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exit_code = 2
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warnings.warn('resource_tracker: %r: %s' % (name, e))
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finally:
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pass
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sys.exit(exit_code)
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