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
|
#! /usr/bin/python
# Copyright (C) 2013 Canonical Ltd.
# Author: Colin Watson <cjwatson@ubuntu.com>
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; version 3 of the License.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program. If not, see <http://www.gnu.org/licenses/>.
"""Atomic counting semaphore files.
This implements two operations, namely test-increment (test non-zero,
increment, return state of test) and decrement-test (decrement, test
non-zero, return state of test), which are sufficient for use as a shared
lock which only opens when all users have unlocked. It is an error to call
decrement-test on a semaphore that is already zero.
The semaphore state is returned on stdout to allow the exit status to be
used to report errors.
"""
from __future__ import print_function
from optparse import OptionParser
import os
import sys
sys.path.insert(0, os.path.join(sys.path[0], os.pardir, "lib"))
from cdimage.semaphore import Semaphore, SemaphoreError
def main():
parser = OptionParser("%prog test-increment|decrement-test SEMAPHORE")
_, args = parser.parse_args()
if len(args) < 1:
parser.error("need operation")
if len(args) < 2:
parser.error("need semaphore file name")
mode, path = args[:2]
semaphore = Semaphore(path)
try:
if mode == "test-increment":
print(semaphore.test_increment())
elif mode == "decrement-test":
print(semaphore.decrement_test())
else:
parser.error("unknown semaphore operation '%s'" % mode)
except SemaphoreError as e:
print(e, file=sys.stderr)
sys.exit(1)
if __name__ == "__main__":
main()
|