/usr/lib/python2.7/dist-packages/Pegasus/tools/filelock.py is in pegasus-wms 4.4.0+dfsg-7.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
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filelock.py: Provides NFS-safe locking around a DB File.
"""
##
# Copyright 2007-2010 University Of Southern California
#
# 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.
##
# Revision : $Revision: 2012 $
import os.path
import time
import random
import anydbm
import atexit
import logging
# Keep list of files to delete
at_exit = {}
def intent_exit_handler():
# Cleanup keys when exiting
for key in at_exit:
try:
logger.debug("unlinking %s" % (key))
os.unlink(key)
except:
logger.debug("error unlinking %s" % (key))
# Get logger object (initialized elsewhere)
logger = logging.getLogger()
class Intent:
"""
The Intent class coordinates intentions between multiple
concurrent site-selector instances. For this reason, it provides
access to a DB file to record arbitrary scalar intentions
into. The file is locked using NFS-safe (so is hoped) file
locks.
"""
def __init__(self):
self.m_filename = None
self.m_pid = os.getpid()
self.m_count = {}
def new(self, fn):
"""
This function records the filename as the database file to
either create or to connect to. If the file does not exist
yet, it will not be created in the initialization
function. However, some simple checks are employed to see, if
the file will be creatable and/or writable, should it not
exist.
"""
# purpose: Initialize class
# paramtr: $fn (IN): path to intent database file
if os.path.isfile(fn):
# File already exists
if os.access(fn, os.R_OK) and os.access(fn, os.W_OK):
# Good!
self.m_filename = fn
return True
else:
# Cannot read/write to file
return False
else:
# File does not exist yet
dir = os.path.dirname(fn)
# Check if directory exists and is writable
if os.path.exists(dir) and os.access(dir, os.W_OK):
# Everything looks good!
self.m_filename = fn
return True
# Failed
return False
def create_lockfile(self, fn):
# Create a lock file NFS-reliably
# warning: use create_lock, not this function
# paramtr: $fn (IN): name of main file to lock
# returns: 1 on success, 0 on failure to lock
tolock = fn
lock = "%s.lock" % (tolock)
uniq = "%s.%d" % (tolock, self.m_pid)
if os.path.isfile(uniq):
logger.warn("Locking: open %s: file already exists" % (uniq))
# os.unlink(uniq)
return False
if os.path.isfile(lock):
logger.warn("Locking: open %s: file already exists" % (lock))
# os.unlink(lock)
return False
try:
my_lock = open(uniq, "w")
except:
logger.warn("Locking: open %s: creating file" % (uniq))
return False
else:
at_exit[uniq] = 1
my_lock.write("%d\n" % (self.m_pid))
my_lock.close()
try:
os.link(uniq, lock)
except:
# Unable to create link, check error
logger.warn("while locking %s" % (uniq))
try:
stats = os.stat(uniq)
except:
# Error, no need to do anything
logger.warn("error trying to stat %s" % uniq)
pass
else:
if stats.st_nlink == 2:
# Lock successful
logger.info("link-count locked")
at_exit[lock] = 1
os.unlink(uniq)
at_exit.pop(uniq)
return True
else:
# Created link
logger.info("hardlinnk locked")
at_exit[lock] = 1
os.unlink(uniq)
at_exit.pop(uniq)
return True
return False
def break_lock(self, fn):
# purpose: check for a dead lock file, and remove if dead
# paramtr: $fn (IN): name of the file to create lock file for
# returns: None if the lock is valid, 1..2 if it was forcefully
# removed, and 0, if it could not be removed.
lock = "%s.lock" % (fn)
# Let's open file and check its pid
try:
input_file = open(lock, 'r')
except:
pass
else:
file_pid = input_file.readline()
file_pid = file_pid.strip()
input_file.close()
# Let's check if said pid is still around
try:
os.kill(int(file_pid), 0)
except:
# Process is not around anymore
if file_pid.isdigit():
uniq = "%s.%d" % (fn, int(file_pid))
logger.info("lock-owner %d found dead, removing lock!" % (int(file_pid)))
os.unlink(lock)
try:
# Also try to remove uniq file
os.unlink(uniq)
except:
pass
# Lock should be broken now
return True
else:
logger.warn("error: cannot determine process id from lock file!")
else:
logger.info("lock-owned %d still lives..." % (int(file_pid)))
# Was not able to break lock
return False
def create_lock(self, fn):
"""
This function attempts to create a file lock around the
specified filename according to Linux conventions. It first
creates a unique file using the process id as unique suffix,
then attempts to hardlink said file to the filename plus
suffix <.lock>. The attempt is randomly backed off to retry
on failure to hardlink. Additionally, the link count is
checked to detect hidden success.
This is a blocking function, and may block indefinitely on
dead-locks, despite occasional lock acquiry wake-ups.
"""
# purpose: blockingly wait for lock file creation
# paramtr: $fn (IN): name of file to create lock file for
# returns: 1: lock was created.
retries = 0
to_wait = 0
while not self.create_lockfile(fn):
if retries > 10:
# We waited enough, let's try to break the lock
self.break_lock(fn)
retries = 0 # Shouldn't be necessary, just in case
else:
# Let's wait for a little while
to_wait = 5 * random.random()
logger.info("lock on file %s is busy, retry %d, waiting %.1f s..." % (fn, retries, to_wait))
time.sleep(to_wait)
retries = retries + 1
logger.info("obtained lock for %s" % (fn))
return True
def delete_lock(self, fn):
"""
This static function deletes all lock files around the given
filename. It should be a fast function, as no waiting is
required.
"""
# purpose: removes a lock file NFS-reliably
# paramtr: $fn (IN): name of main file to lock
# returns: 1 or 2 on success, 0 on failure to unlock
tolock = fn
lock = "%s.lock" % (tolock)
uniq = "%s.%d" % (tolock, self.m_pid)
result = 0
try:
os.unlink(lock)
except:
pass
else:
result = result + 1
at_exit.pop(lock)
try:
os.unlink(uniq)
except:
pass
else:
result = result + 1
at_exit.pop(uniq)
return result
def filename(self):
"""
This is a simple accessor function, returning the filename
that was passed to the constructor.
"""
# purpose: returns the name of the communication file
return self.m_filename
def dbtie(self, ro=False):
"""
This member increases the lock count for the database file,
and connects to the database file.
The return value is the result of the open call. It may be
None in case of failure to open the database.
"""
# purpose: Lock a file and tie it to a hash
# paramtr: $ro (opt. IN): if true, open in read-only mode
# returns: None on error, underlying object otherwise
# Create key if not already there
if not self.m_count.has_key(self.m_pid):
self.m_count[self.m_pid] = 0
if self.m_count[self.m_pid] == 0:
self.create_lock(self.m_filename)
self.m_count[self.m_pid] = self.m_count[self.m_pid] + 1
# Open database in read only or read/write mode
if ro:
my_mode = 'r'
else:
my_mode = 'c'
try:
my_db = anydbm.open(self.m_filename, my_mode)
except:
# Remove lock on failure to connect
self.m_count[self.m_pid] = self.m_count[self.m_pid] - 1
if self.m_count[self.m_pid] == 0:
self.delete_lock(self.m_filename)
return None
return my_db
def locked(self):
"""
This function returns the reference count for locks on the
file. Refernce counters are kept on a per-process basis. This
is not thread safe.
"""
# purpose: detects already tied databases
# returns: reference count for lock
if not self.m_count.has_key(self.m_pid):
return 0
return self.m_count[self.m_pid]
def dbuntie(self, dbref):
"""
This function closes the hash data base and relinquishes the
lock. This method should only be called, if the previous dbtie
operation was successful, similar to opening and closing file
handles
"""
# purpose: untie a hash and release the lock
# paramtr: $dbref (I): reference to db to be closed
# returns: -
self.m_count[self.m_pid] = self.m_count[self.m_pid] - 1
if self.m_count[self.m_pid] == 0:
self.delete_lock(self.m_filename)
# Close datbase
try:
dbref.close()
except:
logger.warn("Error closing %s database" % (m_filename))
def clone(self):
"""
This is a comprehensive function to copy all values from the
database into memory. Please note that you can create nasty
dead-locks this way
"""
# purpose: obtains all current values into a copy
# returns: a hash with key => value, may be empty
# if no keys in database, or None if error
my_copy = {}
my_db = self.dbtie()
if my_db is not None:
# Copy each key/value pair, converting the value to int
for key in my_db.keys():
my_copy[key] = int(my_db[key])
# All done
self.dbuntie(my_db)
return my_copy
return None
def inc(self, key, incr=1):
# purpose: increment the count for a site handle
# paramtr: $key (IN): key of value to increment
# $incr (opt. IN): increment, defaults to 1
# returns: new value, None on error
if key is None:
return None
# Just in case key is not string
key = str(key)
my_db = self.dbtie()
if my_db is not None:
if my_db.has_key(key):
val = int(my_db[key])
val = val + incr
else:
val = incr
# Write new value
my_db[key] = str(val)
# Done, disconnect from data base
self.dbuntie(my_db)
return val
return None
def dec(self, key, decr=1):
# purpose: decrement the count for a site handle
# paramtr: $key (IN): key of value to decrement
# $decr (opt. IN): decrement, defaults to 1
# returns: new value, None in case of error
if key is None:
return None
# Just in case key is not string
key = str(key)
my_db = self.dbtie()
if my_db is not None:
if my_db.has_key(key):
val = int(my_db[key])
val = val - decr
else:
val = decr
# Write new value
my_db[key] = str(val)
# Done, disconnect from data base
self.dbuntie(my_db)
return val
return None
# Register module exit handler
atexit.register(intent_exit_handler)
# Built-in testing
if __name__ == '__main__':
a = Intent()
a.new("/tmp/test1")
# Test tie/untie
b = a.dbtie()
a.dbuntie(b)
# Increment keys
a.inc('usc')
a.inc('usc')
c = a.inc('usc')
if c is None:
print "Cannot get counter!"
else:
print "Counter is now %d" % (c)
c = a.dec("usc", 3)
if c is None:
print "Cannot get counter!"
else:
print "Counter is now %d" % (c)
my_dict = {}
my_dict = a.clone()
for key in my_dict.keys():
print key, "-->", my_dict[key]
print "done"
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