143 lines
5.1 KiB
Python
143 lines
5.1 KiB
Python
# Copyright (c) 2010-2012 OpenStack Foundation
|
|
#
|
|
# Licensed under the Apache License, Version 2.0 (the "License");
|
|
# you may not use this file except in compliance with the License.
|
|
# You may obtain a copy of the License at
|
|
#
|
|
# http://www.apache.org/licenses/LICENSE-2.0
|
|
#
|
|
# Unless required by applicable law or agreed to in writing, software
|
|
# distributed under the License is distributed on an "AS IS" BASIS,
|
|
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
|
|
# implied.
|
|
# See the License for the specific language governing permissions and
|
|
# limitations under the License.
|
|
|
|
import errno
|
|
import fcntl
|
|
import os
|
|
|
|
import eventlet
|
|
import eventlet.debug
|
|
import eventlet.greenthread
|
|
import eventlet.hubs
|
|
|
|
|
|
class PipeMutex(object):
|
|
"""Mutex using a pipe.
|
|
|
|
Works across both greenlets and real threads, even at the same time.
|
|
|
|
Class code copied from Swift's swift/common/utils.py
|
|
Related eventlet bug: https://github.com/eventlet/eventlet/issues/432
|
|
"""
|
|
def __init__(self):
|
|
self.rfd, self.wfd = os.pipe()
|
|
|
|
# You can't create a pipe in non-blocking mode; you must set it
|
|
# later.
|
|
rflags = fcntl.fcntl(self.rfd, fcntl.F_GETFL)
|
|
fcntl.fcntl(self.rfd, fcntl.F_SETFL, rflags | os.O_NONBLOCK)
|
|
os.write(self.wfd, b'-') # start unlocked
|
|
|
|
self.owner = None
|
|
|
|
self.recursion_depth = 0
|
|
# Usually, it's an error to have multiple greenthreads all waiting
|
|
# to read the same file descriptor. It's often a sign of inadequate
|
|
# concurrency control; for example, if you have two greenthreads
|
|
# trying to use the same memcache connection, they'll end up writing
|
|
# interleaved garbage to the socket or stealing part of each others'
|
|
# responses.
|
|
#
|
|
# In this case, we have multiple greenthreads waiting on the same
|
|
# file descriptor by design. This lets greenthreads in real thread A
|
|
# wait with greenthreads in real thread B for the same mutex.
|
|
# Therefore, we must turn off eventlet's multiple-reader detection.
|
|
#
|
|
# It would be better to turn off multiple-reader detection for only
|
|
# our calls to trampoline(), but eventlet does not support that.
|
|
eventlet.debug.hub_prevent_multiple_readers(False)
|
|
|
|
def acquire(self, blocking=True):
|
|
"""Acquire the mutex.
|
|
|
|
If called with blocking=False, returns True if the mutex was
|
|
acquired and False if it wasn't. Otherwise, blocks until the mutex
|
|
is acquired and returns True.
|
|
This lock is recursive; the same greenthread may acquire it as many
|
|
times as it wants to, though it must then release it that many times
|
|
too.
|
|
"""
|
|
current_greenthread_id = id(eventlet.greenthread.getcurrent())
|
|
if self.owner == current_greenthread_id:
|
|
self.recursion_depth += 1
|
|
return True
|
|
|
|
while True:
|
|
try:
|
|
# If there is a byte available, this will read it and remove
|
|
# it from the pipe. If not, this will raise OSError with
|
|
# errno=EAGAIN.
|
|
os.read(self.rfd, 1)
|
|
self.owner = current_greenthread_id
|
|
return True
|
|
except OSError as err:
|
|
if err.errno != errno.EAGAIN:
|
|
raise
|
|
|
|
if not blocking:
|
|
return False
|
|
|
|
# Tell eventlet to suspend the current greenthread until
|
|
# self.rfd becomes readable. This will happen when someone
|
|
# else writes to self.wfd.
|
|
eventlet.hubs.trampoline(self.rfd, read=True)
|
|
|
|
def release(self):
|
|
"""Release the mutex."""
|
|
current_greenthread_id = id(eventlet.greenthread.getcurrent())
|
|
if self.owner != current_greenthread_id:
|
|
raise RuntimeError("cannot release un-acquired lock")
|
|
|
|
if self.recursion_depth > 0:
|
|
self.recursion_depth -= 1
|
|
return
|
|
|
|
self.owner = None
|
|
os.write(self.wfd, b'X')
|
|
|
|
def close(self):
|
|
"""Close the mutex.
|
|
|
|
This releases its file descriptors.
|
|
You can't use a mutex after it's been closed.
|
|
"""
|
|
if self.wfd is not None:
|
|
os.close(self.wfd)
|
|
self.wfd = None
|
|
if self.rfd is not None:
|
|
os.close(self.rfd)
|
|
self.rfd = None
|
|
self.owner = None
|
|
self.recursion_depth = 0
|
|
|
|
def __del__(self):
|
|
# We need this so we don't leak file descriptors. Otherwise, if you
|
|
# call get_logger() and don't explicitly dispose of it by calling
|
|
# logger.logger.handlers[0].lock.close() [1], the pipe file
|
|
# descriptors are leaked.
|
|
#
|
|
# This only really comes up in tests. Service processes tend to call
|
|
# get_logger() once and then hang on to it until they exit, but the
|
|
# test suite calls get_logger() a lot.
|
|
#
|
|
# [1] and that's a completely ridiculous thing to expect callers to
|
|
# do, so nobody does it and that's okay.
|
|
self.close()
|
|
|
|
|
|
def pipe_createLock(self):
|
|
"""Replacement for logging.Handler.createLock method."""
|
|
self.lock = PipeMutex()
|