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python3.14
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multiprocessing
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resource_tracker.py
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############################################################################### # 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 base64 import os import signal import sys import threading import warnings from collections import deque import json from . import spawn from . import util __all__ = ['ensure_running', 'register', 'unregister'] _HAVE_SIGMASK = hasattr(signal, 'pthread_sigmask') _IGNORED_SIGNALS = (signal.SIGINT, signal.SIGTERM) def cleanup_noop(name): raise RuntimeError('noop should never be registered or cleaned up') _CLEANUP_FUNCS = { 'noop': cleanup_noop, 'dummy': lambda name: None, # Dummy resource used in tests } 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['semaphore'] = _multiprocessing.sem_unlink _CLEANUP_FUNCS['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 self._exitcode = None self._reentrant_messages = deque() # True to use colon-separated lines, rather than JSON lines, # for internal communication. (Mainly for testing). # Filenames not supported by the simple format will always be sent # using JSON. # The reader should understand all formats. self._use_simple_format = True 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: raise 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 try: _, status = waitpid(self._pid, 0) except ChildProcessError: self._pid = None self._exitcode = None return self._pid = None try: self._exitcode = waitstatus_to_exitcode(status) except ValueError: # os.waitstatus_to_exitcode may raise an exception for invalid values self._exitcode = 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.''' return self._ensure_running_and_write() def _teardown_dead_process(self): 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 self._exitcode = None warnings.warn('resource_tracker: process died unexpectedly, ' 'relaunching. Some resources might leak.') def _launch(self): fds_to_pass = [] try: fds_to_pass.append(sys.stderr.fileno()) except Exception: pass 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(), '-c', f'from multiprocessing.resource_tracker import main;main({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 _make_probe_message(self): """Return a probe message.""" if self._use_simple_format: return b'PROBE:0:noop\n' return ( json.dumps( {"cmd": "PROBE", "rtype": "noop"}, ensure_ascii=True, separators=(",", ":"), ) + "\n" ).encode("ascii") def _ensure_running_and_write(self, msg=None): with self._lock: if self._lock._recursion_count() > 1: # The code below is certainly not reentrant-safe, so bail out if msg is None: raise self._reentrant_call_error() return self._reentrant_messages.append(msg) if self._fd is not None: # resource tracker was launched before, is it still running? if msg is None: to_send = self._make_probe_message() else: to_send = msg try: self._write(to_send) except OSError: self._teardown_dead_process() self._launch() msg = None # message was sent in probe else: self._launch() while True: try: reentrant_msg = self._reentrant_messages.popleft() except IndexError: break self._write(reentrant_msg) if msg is not None: self._write(msg) 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, self._make_probe_message()) 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 _write(self, msg): nbytes = os.write(self._fd, msg) assert nbytes == len(msg), f"{nbytes=} != {len(msg)=}" def _send(self, cmd, name, rtype): if self._use_simple_format and '\n' not in name: msg = f"{cmd}:{name}:{rtype}\n".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') self._ensure_running_and_write(msg) return # POSIX guarantees that writes to a pipe of less than PIPE_BUF (512 on Linux) # bytes are atomic. Therefore, we want the message to be shorter than 512 bytes. # POSIX shm_open() and sem_open() require the name, including its leading slash, # to be at most NAME_MAX bytes (255 on Linux) # With json.dump(..., ensure_ascii=True) every non-ASCII byte becomes a 6-char # escape like \uDC80. # As we want the overall message to be kept atomic and therefore smaller than 512, # we encode encode the raw name bytes with URL-safe Base64 - so a 255 long name # will not exceed 340 bytes. b = name.encode('utf-8', 'surrogateescape') if len(b) > 255: raise ValueError('shared memory name too long (max 255 bytes)') b64 = base64.urlsafe_b64encode(b).decode('ascii') payload = {"cmd": cmd, "rtype": rtype, "base64_name": b64} msg = (json.dumps(payload, ensure_ascii=True, separators=(",", ":")) + "\n").encode("ascii") # The entire JSON message is guaranteed < PIPE_BUF (512 bytes) by construction. assert len(msg) <= 512, f"internal error: message too long ({len(msg)} bytes)" assert msg.startswith(b'{') self._ensure_running_and_write(msg) _resource_tracker = ResourceTracker() ensure_running = _resource_tracker.ensure_running register = _resource_tracker.register unregister = _resource_tracker.unregister getfd = _resource_tracker.getfd def _decode_message(line): if line.startswith(b'{'): try: obj = json.loads(line.decode('ascii')) except Exception as e: raise ValueError("malformed resource_tracker message: %r" % (line,)) from e cmd = obj["cmd"] rtype = obj["rtype"] b64 = obj.get("base64_name", "") if not isinstance(cmd, str) or not isinstance(rtype, str) or not isinstance(b64, str): raise ValueError("malformed resource_tracker fields: %r" % (obj,)) try: name = base64.urlsafe_b64decode(b64).decode('utf-8', 'surrogateescape') except ValueError as e: raise ValueError("malformed resource_tracker base64_name: %r" % (b64,)) from e else: cmd, rest = line.strip().decode('ascii').split(':', maxsplit=1) name, rtype = rest.rsplit(':', maxsplit=1) return cmd, rtype, name 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()} exit_code = 0 try: # keep track of registered/unregistered resources with open(fd, 'rb') as f: for line in f: try: cmd, rtype, name = _decode_message(line) 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: exit_code = 3 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: exit_code = 1 if rtype == 'dummy': # The test 'dummy' resource is expected to leak. # We skip the warning (and *only* the warning) for it. pass else: warnings.warn( f'resource_tracker: There appear to be ' f'{len(rtype_cache)} leaked {rtype} objects to ' f'clean up at shutdown: {rtype_cache}' ) 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: exit_code = 2 warnings.warn('resource_tracker: %r: %s' % (name, e)) finally: pass sys.exit(exit_code)