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Editing: resource_tracker.py
############################################################################### # Server process to keep track of unlinked resources (like shared memory # segments, semaphores etc.) and clean them. # # On Unix we run a server process which keeps track of unlinked # resources. The server ignores SIGINT and SIGTERM and reads from a # pipe. Every other process of the program has a copy of the writable # end of the pipe, so we get EOF when all other processes have exited. # Then the server process unlinks any remaining resource names. # # This is important because there may be system limits for such resources: for # instance, the system only supports a limited number of named semaphores, and # shared-memory segments live in the RAM. If a python process leaks such a # resource, this resource will not be removed till the next reboot. Without # this resource tracker process, "killall python" would probably leave unlinked # resources. import os import signal import sys import threading import warnings from . import spawn from . import util __all__ = ['ensure_running', 'register', 'unregister'] _HAVE_SIGMASK = hasattr(signal, 'pthread_sigmask') _IGNORED_SIGNALS = (signal.SIGINT, signal.SIGTERM) _CLEANUP_FUNCS = { 'noop': lambda: None, } if os.name == 'posix': import _multiprocessing import _posixshmem # Use sem_unlink() to clean up named semaphores. # # sem_unlink() may be missing if the Python build process detected the # absence of POSIX named semaphores. In that case, no named semaphores were # ever opened, so no cleanup would be necessary. if hasattr(_multiprocessing, 'sem_unlink'): _CLEANUP_FUNCS.update({ 'semaphore': _multiprocessing.sem_unlink, }) _CLEANUP_FUNCS.update({ 'shared_memory': _posixshmem.shm_unlink, }) class ReentrantCallError(RuntimeError): pass class ResourceTracker(object): def __init__(self): self._lock = threading.RLock() self._fd = None self._pid = None def _reentrant_call_error(self): # gh-109629: this happens if an explicit call to the ResourceTracker # gets interrupted by a garbage collection, invoking a finalizer (*) # that itself calls back into ResourceTracker. # (*) for example the SemLock finalizer raise ReentrantCallError( "Reentrant call into the multiprocessing resource tracker") def __del__(self): # making sure child processess are cleaned before ResourceTracker # gets destructed. # see https://github.com/python/cpython/issues/88887 self._stop(use_blocking_lock=False) def _stop(self, use_blocking_lock=True): if use_blocking_lock: with self._lock: self._stop_locked() else: acquired = self._lock.acquire(blocking=False) try: self._stop_locked() finally: if acquired: self._lock.release() def _stop_locked( self, close=os.close, waitpid=os.waitpid, waitstatus_to_exitcode=os.waitstatus_to_exitcode, ): # This shouldn't happen (it might when called by a finalizer) # so we check for it anyway. if self._lock._recursion_count() > 1: return self._reentrant_call_error() if self._fd is None: # not running return if self._pid is None: return # closing the "alive" file descriptor stops main() close(self._fd) self._fd = None waitpid(self._pid, 0) self._pid = None def getfd(self): self.ensure_running() return self._fd def ensure_running(self): '''Make sure that resource tracker process is running. This can be run from any process. Usually a child process will use the resource created by its parent.''' with self._lock: if self._lock._recursion_count() > 1: # The code below is certainly not reentrant-safe, so bail out return self._reentrant_call_error() if self._fd is not None: # resource tracker was launched before, is it still running? if self._check_alive(): # => still alive return # => dead, launch it again os.close(self._fd) # Clean-up to avoid dangling processes. try: # _pid can be None if this process is a child from another # python process, which has started the resource_tracker. if self._pid is not None: os.waitpid(self._pid, 0) except ChildProcessError: # The resource_tracker has already been terminated. pass self._fd = None self._pid = None warnings.warn('resource_tracker: process died unexpectedly, ' 'relaunching. Some resources might leak.') fds_to_pass = [] try: fds_to_pass.append(sys.stderr.fileno()) except Exception: pass cmd = 'from multiprocessing.resource_tracker import main;main(%d)' r, w = os.pipe() try: fds_to_pass.append(r) # process will out live us, so no need to wait on pid exe = spawn.get_executable() args = [exe] + util._args_from_interpreter_flags() args += ['-c', cmd % r] # bpo-33613: Register a signal mask that will block the signals. # This signal mask will be inherited by the child that is going # to be spawned and will protect the child from a race condition # that can make the child die before it registers signal handlers # for SIGINT and SIGTERM. The mask is unregistered after spawning # the child. prev_sigmask = None try: if _HAVE_SIGMASK: prev_sigmask = signal.pthread_sigmask(signal.SIG_BLOCK, _IGNORED_SIGNALS) pid = util.spawnv_passfds(exe, args, fds_to_pass) finally: if prev_sigmask is not None: signal.pthread_sigmask(signal.SIG_SETMASK, prev_sigmask) except: os.close(w) raise else: self._fd = w self._pid = pid finally: os.close(r) def _check_alive(self): '''Check that the pipe has not been closed by sending a probe.''' try: # We cannot use send here as it calls ensure_running, creating # a cycle. os.write(self._fd, b'PROBE:0:noop\n') except OSError: return False else: return True def register(self, name, rtype): '''Register name of resource with resource tracker.''' self._send('REGISTER', name, rtype) def unregister(self, name, rtype): '''Unregister name of resource with resource tracker.''' self._send('UNREGISTER', name, rtype) def _send(self, cmd, name, rtype): try: self.ensure_running() except ReentrantCallError: # The code below might or might not work, depending on whether # the resource tracker was already running and still alive. # Better warn the user. # (XXX is warnings.warn itself reentrant-safe? :-) warnings.warn( f"ResourceTracker called reentrantly for resource cleanup, " f"which is unsupported. " f"The {rtype} object {name!r} might leak.") msg = '{0}:{1}:{2}\n'.format(cmd, name, rtype).encode('ascii') if len(msg) > 512: # posix guarantees that writes to a pipe of less than PIPE_BUF # bytes are atomic, and that PIPE_BUF >= 512 raise ValueError('msg too long') nbytes = os.write(self._fd, msg) assert nbytes == len(msg), "nbytes {0:n} but len(msg) {1:n}".format( nbytes, len(msg)) _resource_tracker = ResourceTracker() ensure_running = _resource_tracker.ensure_running register = _resource_tracker.register unregister = _resource_tracker.unregister getfd = _resource_tracker.getfd def main(fd): '''Run resource tracker.''' # protect the process from ^C and "killall python" etc signal.signal(signal.SIGINT, signal.SIG_IGN) signal.signal(signal.SIGTERM, signal.SIG_IGN) if _HAVE_SIGMASK: signal.pthread_sigmask(signal.SIG_UNBLOCK, _IGNORED_SIGNALS) for f in (sys.stdin, sys.stdout): try: f.close() except Exception: pass cache = {rtype: set() for rtype in _CLEANUP_FUNCS.keys()} try: # keep track of registered/unregistered resources with open(fd, 'rb') as f: for line in f: try: cmd, name, rtype = line.strip().decode('ascii').split(':') cleanup_func = _CLEANUP_FUNCS.get(rtype, None) if cleanup_func is None: raise ValueError( f'Cannot register {name} for automatic cleanup: ' f'unknown resource type {rtype}') if cmd == 'REGISTER': cache[rtype].add(name) elif cmd == 'UNREGISTER': cache[rtype].remove(name) elif cmd == 'PROBE': pass else: raise RuntimeError('unrecognized command %r' % cmd) except Exception: try: sys.excepthook(*sys.exc_info()) except: pass finally: # all processes have terminated; cleanup any remaining resources for rtype, rtype_cache in cache.items(): if rtype_cache: try: warnings.warn('resource_tracker: There appear to be %d ' 'leaked %s objects to clean up at shutdown' % (len(rtype_cache), rtype)) except Exception: pass for name in rtype_cache: # For some reason the process which created and registered this # resource has failed to unregister it. Presumably it has # died. We therefore unlink it. try: try: _CLEANUP_FUNCS[rtype](name) except Exception as e: warnings.warn('resource_tracker: %r: %s' % (name, e)) finally: pass
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