/usr/lib/python3/dist-packages/twisted/python/lockfile.py is in python3-twisted-experimental 13.2.0-0ubuntu1.
This file is owned by root:root, with mode 0o644.
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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 | # -*- test-case-name: twisted.test.test_lockfile -*-
# Copyright (c) 2005 Divmod, Inc.
# Copyright (c) Twisted Matrix Laboratories.
# See LICENSE for details.
"""
Filesystem-based interprocess mutex.
"""
__metaclass__ = type
import errno, os
from time import time as _uniquefloat
from twisted.python.runtime import platform
def unique():
return str(int(_uniquefloat() * 1000))
from os import rename
if not platform.isWindows():
from os import kill
from os import symlink
from os import readlink
from os import remove as rmlink
_windows = False
else:
_windows = True
try:
from win32api import OpenProcess
import pywintypes
except ImportError:
kill = None
else:
ERROR_ACCESS_DENIED = 5
ERROR_INVALID_PARAMETER = 87
def kill(pid, signal):
try:
OpenProcess(0, 0, pid)
except pywintypes.error as e:
if e.args[0] == ERROR_ACCESS_DENIED:
return
elif e.args[0] == ERROR_INVALID_PARAMETER:
raise OSError(errno.ESRCH, None)
raise
else:
raise RuntimeError("OpenProcess is required to fail.")
_open = file
# XXX Implement an atomic thingamajig for win32
def symlink(value, filename):
newlinkname = filename+"."+unique()+'.newlink'
newvalname = os.path.join(newlinkname,"symlink")
os.mkdir(newlinkname)
f = _open(newvalname,'wcb')
f.write(value)
f.flush()
f.close()
try:
rename(newlinkname, filename)
except:
os.remove(newvalname)
os.rmdir(newlinkname)
raise
def readlink(filename):
try:
fObj = _open(os.path.join(filename,'symlink'), 'rb')
except IOError as e:
if e.errno == errno.ENOENT or e.errno == errno.EIO:
raise OSError(e.errno, None)
raise
else:
result = fObj.read()
fObj.close()
return result
def rmlink(filename):
os.remove(os.path.join(filename, 'symlink'))
os.rmdir(filename)
class FilesystemLock:
"""
A mutex.
This relies on the filesystem property that creating
a symlink is an atomic operation and that it will
fail if the symlink already exists. Deleting the
symlink will release the lock.
@ivar name: The name of the file associated with this lock.
@ivar clean: Indicates whether this lock was released cleanly by its
last owner. Only meaningful after C{lock} has been called and
returns True.
@ivar locked: Indicates whether the lock is currently held by this
object.
"""
clean = None
locked = False
def __init__(self, name):
self.name = name
def lock(self):
"""
Acquire this lock.
@rtype: C{bool}
@return: True if the lock is acquired, false otherwise.
@raise: Any exception os.symlink() may raise, other than
EEXIST.
"""
clean = True
while True:
try:
symlink(str(os.getpid()), self.name)
except OSError as e:
if _windows and e.errno in (errno.EACCES, errno.EIO):
# The lock is in the middle of being deleted because we're
# on Windows where lock removal isn't atomic. Give up, we
# don't know how long this is going to take.
return False
if e.errno == errno.EEXIST:
try:
pid = readlink(self.name)
except OSError as e:
if e.errno == errno.ENOENT:
# The lock has vanished, try to claim it in the
# next iteration through the loop.
continue
raise
except IOError as e:
if _windows and e.errno == errno.EACCES:
# The lock is in the middle of being
# deleted because we're on Windows where
# lock removal isn't atomic. Give up, we
# don't know how long this is going to
# take.
return False
raise
try:
if kill is not None:
kill(int(pid), 0)
except OSError as e:
if e.errno == errno.ESRCH:
# The owner has vanished, try to claim it in the next
# iteration through the loop.
try:
rmlink(self.name)
except OSError as e:
if e.errno == errno.ENOENT:
# Another process cleaned up the lock.
# Race them to acquire it in the next
# iteration through the loop.
continue
raise
clean = False
continue
raise
return False
raise
self.locked = True
self.clean = clean
return True
def unlock(self):
"""
Release this lock.
This deletes the directory with the given name.
@raise: Any exception os.readlink() may raise, or
ValueError if the lock is not owned by this process.
"""
pid = readlink(self.name)
if int(pid) != os.getpid():
raise ValueError("Lock %r not owned by this process" % (self.name,))
rmlink(self.name)
self.locked = False
def isLocked(name):
"""Determine if the lock of the given name is held or not.
@type name: C{str}
@param name: The filesystem path to the lock to test
@rtype: C{bool}
@return: True if the lock is held, False otherwise.
"""
l = FilesystemLock(name)
result = None
try:
result = l.lock()
finally:
if result:
l.unlock()
return not result
__all__ = ['FilesystemLock', 'isLocked']
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