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"""Garbage collection thread for representing zmq refcount of Python objects
used in zero-copy sends.
"""
# Copyright (C) PyZMQ Developers
# Distributed under the terms of the Modified BSD License.
import atexit
import struct
from os import getpid
from collections import namedtuple
from threading import Thread, Event, Lock
import warnings
import zmq
gcref = namedtuple('gcref', ['obj', 'event'])
class GarbageCollectorThread(Thread):
"""Thread in which garbage collection actually happens."""
def __init__(self, gc):
super(GarbageCollectorThread, self).__init__()
self.gc = gc
self.daemon = True
self.pid = getpid()
self.ready = Event()
def run(self):
# detect fork at begining of the thread
if getpid is None or getpid() != self.pid:
self.ready.set()
return
try:
s = self.gc.context.socket(zmq.PULL)
s.linger = 0
s.bind(self.gc.url)
finally:
self.ready.set()
while True:
# detect fork
if getpid is None or getpid() != self.pid:
return
msg = s.recv()
if msg == b'DIE':
break
fmt = 'L' if len(msg) == 4 else 'Q'
key = struct.unpack(fmt, msg)[0]
tup = self.gc.refs.pop(key, None)
if tup and tup.event:
tup.event.set()
del tup
s.close()
class GarbageCollector(object):
"""PyZMQ Garbage Collector
Used for representing the reference held by libzmq during zero-copy sends.
This object holds a dictionary, keyed by Python id,
of the Python objects whose memory are currently in use by zeromq.
When zeromq is done with the memory, it sends a message on an inproc PUSH socket
containing the packed size_t (32 or 64-bit unsigned int),
which is the key in the dict.
When the PULL socket in the gc thread receives that message,
the reference is popped from the dict,
and any tracker events that should be signaled fire.
"""
refs = None
_context = None
_lock = None
url = "inproc://pyzmq.gc.01"
def __init__(self, context=None):
super(GarbageCollector, self).__init__()
self.refs = {}
self.pid = None
self.thread = None
self._context = context
self._lock = Lock()
self._stay_down = False
atexit.register(self._atexit)
@property
def context(self):
if self._context is None:
self._context = zmq.Context()
return self._context
@context.setter
def context(self, ctx):
if self.is_alive():
if self.refs:
warnings.warn("Replacing gc context while gc is running", RuntimeWarning)
self.stop()
self._context = ctx
def _atexit(self):
"""atexit callback
sets _stay_down flag so that gc doesn't try to start up again in other atexit handlers
"""
self._stay_down = True
self.stop()
def stop(self):
"""stop the garbage-collection thread"""
if not self.is_alive():
return
self._stop()
def _stop(self):
push = self.context.socket(zmq.PUSH)
push.connect(self.url)
push.send(b'DIE')
push.close()
self.thread.join()
self.context.term()
self.refs.clear()
self.context = None
def start(self):
"""Start a new garbage collection thread.
Creates a new zmq Context used for garbage collection.
Under most circumstances, this will only be called once per process.
"""
if self.thread is not None and self.pid != getpid():
# It's re-starting, must free earlier thread's context
# since a fork probably broke it
self._stop()
self.pid = getpid()
self.refs = {}
self.thread = GarbageCollectorThread(self)
self.thread.start()
self.thread.ready.wait()
def is_alive(self):
"""Is the garbage collection thread currently running?
Includes checks for process shutdown or fork.
"""
if (getpid is None or
getpid() != self.pid or
self.thread is None or
not self.thread.is_alive()
):
return False
return True
def store(self, obj, event=None):
"""store an object and (optionally) event for zero-copy"""
if not self.is_alive():
if self._stay_down:
return 0
# safely start the gc thread
# use lock and double check,
# so we don't start multiple threads
with self._lock:
if not self.is_alive():
self.start()
tup = gcref(obj, event)
theid = id(tup)
self.refs[theid] = tup
return theid
def __del__(self):
if not self.is_alive():
return
try:
self.stop()
except Exception as e:
raise (e)
gc = GarbageCollector()
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