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filequeue.py
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filequeue.py
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# -*- coding: utf-8 -*-
# pylint: disable=visually-indented-line-with-same-indent-as-next-logical-line
# pylint: disable=too-few-public-methods,modernize-parse-error,no-else-return
"""
The queue runner in salt uses sqlite. While not a problem in general, when
a few events arrive simultaneously, the last attempts fail. The contention is
around the connection which raises the exception "OperationalError: database is
locked". Increasing timeouts, moving the database to tmpfs or adding retry
logic is moving the problem.
This runner will rely on file existence, creation and removal. If a system
is loaded, operations will block but eventually complete.
"""
from __future__ import absolute_import
from __future__ import print_function
import time
import logging
import os
import glob
import salt.loader
import salt.utils.event
import salt.ext.six as six
log = logging.getLogger(__name__)
class FileQueue(object):
"""
Use fileystem operations to keep track of a queue. Rely on modification
time for order.
"""
def __init__(self, **kwargs):
"""
Set default settings, allow overriding, create queue directory
"""
self.settings = {'root_dir': "/var/cache/salt/master/filequeues",
'queue': "default",
'event': "salt/filequeue/queue"}
if 'queue' in kwargs:
self.settings['event'] = "salt/filequeue/" + kwargs['queue']
# Do not include the operation if the event is overridden
if 'event' in kwargs:
self.include_operation = False
else:
self.include_operation = True
self.settings.update(kwargs)
self.root_dir = self.settings['root_dir']
queue = self.settings['queue']
self.queue_dir = "{}/{}".format(self.root_dir, queue)
if not os.path.isdir(self.queue_dir):
log.info("creating {}".format(self.queue_dir))
os.makedirs(self.queue_dir)
def dirs(self):
"""
List directories under root_dir
"""
dirs = glob.glob("{}/*".format(self.root_dir))
dirs = [os.path.basename(d) for d in dirs]
return dirs
def touch(self, item):
"""
Create or update filename. Return based on duplicate_fail.
"""
filename = "{}/{}".format(self.queue_dir, item)
ret = os.path.isfile(filename)
with open(filename, "w") as entry:
log.info("creating {}".format(filename))
entry.write("")
if (ret and 'duplicate_fail' in self.settings and
self.settings['duplicate_fail']):
self._fire_event(False, [item, "present"])
return False
self._fire_event(True, [item, "added"])
return True
# pylint: disable=invalid-name
def ls(self):
"""
List filenames in alpha-numeric order
"""
files = glob.glob("{}/*".format(self.queue_dir))
files = [os.path.basename(f) for f in files]
return sorted(files)
def items(self):
"""
List filenames in modification time order
"""
mtime = {}
for filename in os.listdir(self.queue_dir):
mtime[os.stat("{}/{}".format(self.queue_dir, filename)).st_mtime] = filename
files = [mtime[k] for k in sorted(mtime.keys())]
return files
def empty(self):
"""
Check if no files are present
"""
files = self.ls()
if files:
log.debug("queue {} contains {}".format(self.queue_dir, files))
self._fire_event(False, ["populated"])
return False
else:
log.debug("queue {} is empty".format(self.queue_dir))
self._fire_event(True, ["empty"])
return True
def remove(self, item):
"""
Remove file
"""
filename = "{}/{}".format(self.queue_dir, item)
if os.path.isfile(filename):
log.debug("removing {}".format(filename))
os.remove(filename)
self._fire_event(True, [item, "remove"])
return True
self._fire_event(False, [item, "absent"])
return False
def vacate(self, item):
"""
Remove file and check if empty in a single operation
Note: Timing in Salt events creates race conditions if remove and empty
are called separately from the same reactor file.
"""
files = self.ls()
log.debug("queue {} contains {}".format(self.queue_dir, files))
filename = "{}/{}".format(self.queue_dir, item)
if os.path.isfile(filename):
log.debug("deleting {}".format(filename))
os.remove(filename)
if len(files) == 1:
if files[0] == item:
log.debug("queue {} is vacated".format(self.queue_dir))
self._fire_event(True, ["vacated"])
return True
else:
log.debug("queue {} contains {}".format(self.queue_dir, files))
self._fire_event(False, ["occupied"])
return False
else:
log.debug("filename {} does not exist".format(filename))
return None
def check(self, item):
"""
Return whether the file exists
"""
filename = "{}/{}".format(self.queue_dir, item)
ret = os.path.isfile(filename)
if ret:
log.info("file {} exists".format(filename))
self._fire_event(True, [item, "exists"])
else:
log.info("file {} is missing".format(filename))
self._fire_event(False, [item, "missing"])
return ret
def _fire_event(self, result, operation):
"""
Fire optional Salt event for some operations. Always send an
event unless 'fire_on' is set. Then, only send an event when
matching
"""
if 'fire' in self.settings and not self.settings['fire']:
return
settings = _skip_dunder(self.settings)
tags = settings['event'].split('/')
if self.include_operation:
tags += operation
log.info("firing event for {}".format("/".join(tags)))
if ('fire_on' not in settings or
'fire_on' in settings and settings['fire_on'] == result):
event = salt.utils.event.SaltEvent('master', __opts__['sock_dir'])
event.fire_event(settings, "/".join(tags))
class Lock(object):
"""
Serialize operations on queue
"""
def __init__(self, settings):
"""
Derive lockfile from settings
"""
self.lockfile = "{}/.{}.lock".format(settings['root_dir'], settings['queue'])
log.info("locking {}".format(self.lockfile))
def __enter__(self):
"""
Symlink makes a cheap semaphore
"""
while True:
try:
os.symlink("/dev/null", self.lockfile)
break
except OSError:
log.debug("{} locked".format(self.lockfile))
time.sleep(.2)
return
def __exit__(self, type_, value, traceback):
"""
Remove symlink
"""
os.remove(self.lockfile)
def _skip_dunder(settings):
"""
Skip double underscore keys
"""
return {k: v for k, v in six.iteritems(settings) if not k.startswith('__')}
def help_():
"""
Usage
"""
usage = ('filequeue.queues:\n\n'
' List the existing queues\n\n'
' CLI Example:\n\n'
' salt-run filequeue.queues\n'
'\n\n'
'filequeue.enqueue:\n'
'filequeue.add:\n'
'filequeue.push:\n\n'
' Add an item on to a queue\n\n'
' CLI Example:\n\n'
' salt-run filequeue.enqueue abc\n'
' salt-run filequeue.enqueue abc queue=prep\n'
' salt-run filequeue.enqueue item=abc queue=prep\n'
' salt-run filequeue.add abc\n'
' salt-run filequeue.add abc queue=prep\n'
' salt-run filequeue.add item=abc queue=prep\n'
' salt-run filequeue.push abc\n'
' salt-run filequeue.push abc queue=prep\n'
' salt-run filequeue.push item=abc queue=prep\n'
'\n\n'
'filequeue.dequeue:\n\n'
' Remove and return oldest item from a queue\n\n'
' CLI Example:\n\n'
' salt-run filequeue.dequeue\n'
' salt-run filequeue.dequeue queue=prep\n'
'\n\n'
'filequeue.pop:\n\n'
' Remove and return newest item from a queue\n\n'
' CLI Example:\n\n'
' salt-run filequeue.pop\n'
' salt-run filequeue.pop queue=prep\n'
'\n\n'
'filequeue.ls:\n\n'
' List items in a queue\n\n'
' CLI Example:\n\n'
' salt-run filequeue.ls\n'
'\n\n'
'filequeue.items:\n\n'
' List items in mtime order in a queue\n\n'
' CLI Example:\n\n'
' salt-run filequeue.items\n'
'\n\n'
'filequeue.empty:\n\n'
' Check if a queue is empty\n\n'
' CLI Example:\n\n'
' salt-run filequeue.empty\n'
'\n\n'
'filequeue.check:\n\n'
' Check if an item is in a queue\n\n'
' CLI Example:\n\n'
' salt-run filequeue.check abc\n'
' salt-run filequeue.check abc queue=prep\n'
' salt-run filequeue.check item=abc queue=prep\n'
'\n\n'
'filequeue.remove:\n\n'
' Remove an item from a queue\n\n'
' CLI Example:\n\n'
' salt-run filequeue.remove abc\n'
' salt-run filequeue.remove abc queue=prep\n'
' salt-run filequeue.remove item=abc queue=prep\n'
'\n\n'
'filequeue.vacant:\n\n'
' Remove an item and check if queue is empty\n\n'
' CLI Example:\n\n'
' salt-run filequeue.vacant abc\n'
' salt-run filequeue.vacant abc queue=prep\n'
' salt-run filequeue.vacant item=abc queue=prep\n')
print(usage)
return ""
def queues(**kwargs):
"""
List queues
"""
log.debug("queues: kwargs = {}".format(_skip_dunder(kwargs)))
filequeue = FileQueue(**kwargs)
with Lock(filequeue.settings):
return "\n".join(filequeue.dirs())
def enqueue(queue=None, **kwargs):
"""
Add item
"""
log.debug("enqueue: queue = {}, kwargs = {}".format(queue, _skip_dunder(kwargs)))
filequeue = FileQueue(**kwargs)
with Lock(filequeue.settings):
if queue:
ret = filequeue.touch(queue)
elif 'item' in kwargs:
ret = filequeue.touch(kwargs['item'])
else:
help()
return None
return ret
def add(queue=None, **kwargs):
"""
Alias for enqueue
"""
return enqueue(queue, **kwargs)
def push(queue=None, **kwargs):
"""
Alias for enqueue
"""
return enqueue(queue, **kwargs)
# pylint: disable=invalid-name
def dequeue(**kwargs):
"""
Remove oldest item
"""
log.debug("dequeue: kwargs = {}".format(_skip_dunder(kwargs)))
filequeue = FileQueue(**kwargs)
with Lock(filequeue.settings):
oldest = list(filequeue.items())[0]
filequeue.remove(oldest)
return oldest
def pop(**kwargs):
"""
Remove newest item
"""
log.debug("pop: kwargs = {}".format(_skip_dunder(kwargs)))
filequeue = FileQueue(**kwargs)
with Lock(filequeue.settings):
newest = list(filequeue.items())[-1]
filequeue.remove(newest)
return newest
# pylint: disable=invalid-name
def ls(**kwargs):
"""
List items
"""
log.debug("ls: kwargs = {}".format(_skip_dunder(kwargs)))
filequeue = FileQueue(**kwargs)
with Lock(filequeue.settings):
return "\n".join(filequeue.ls())
def items(**kwargs):
"""
List items in time order
"""
log.debug("items: kwargs = {}".format(_skip_dunder(kwargs)))
filequeue = FileQueue(**kwargs)
with Lock(filequeue.settings):
return "\n".join(list(filequeue.items()))
def empty(**kwargs):
"""
Check if queue is empty
"""
log.debug("empty: kwargs = {}".format(_skip_dunder(kwargs)))
filequeue = FileQueue(**kwargs)
with Lock(filequeue.settings):
return filequeue.empty()
def check(queue=None, **kwargs):
"""
Check if item exists
"""
log.debug("check: queue = {}, kwargs = {}".format(queue, _skip_dunder(kwargs)))
filequeue = FileQueue(**kwargs)
with Lock(filequeue.settings):
if queue:
return filequeue.check(queue)
elif 'item' in kwargs:
return filequeue.check(kwargs['item'])
else:
help()
return None
def remove(queue=None, **kwargs):
"""
Remove specific item
"""
log.debug("remove: queue = {}, kwargs = {}".format(queue, _skip_dunder(kwargs)))
filequeue = FileQueue(**kwargs)
with Lock(filequeue.settings):
if queue:
return filequeue.remove(queue)
elif 'item' in kwargs:
return filequeue.remove(kwargs['item'])
else:
help()
return None
def vacate(queue=None, **kwargs):
"""
Remove specific item and check if queue is empty
"""
log.debug("vacate: queue = {}, kwargs = {}".format(queue, _skip_dunder(kwargs)))
filequeue = FileQueue(**kwargs)
with Lock(filequeue.settings):
if queue:
return filequeue.vacate(queue)
elif 'item' in kwargs:
return filequeue.vacate(kwargs['item'])
else:
help()
return None
__func_alias__ = {
'help_': 'help',
}