blob: 9c50673418fad65243b4f657963df021622c584c (
plain)
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
|
from __future__ import absolute_import
import time
import os
from . import (LockBase, LockFailed, NotLocked, NotMyLock, LockTimeout,
AlreadyLocked)
class LinkLockFile(LockBase):
"""Lock access to a file using atomic property of link(2).
>>> lock = LinkLockFile('somefile')
>>> lock = LinkLockFile('somefile', threaded=False)
"""
def acquire(self, timeout=None):
try:
open(self.unique_name, "wb").close()
except IOError:
raise LockFailed("failed to create %s" % self.unique_name)
timeout = timeout is not None and timeout or self.timeout
end_time = time.time()
if timeout is not None and timeout > 0:
end_time += timeout
while True:
# Try and create a hard link to it.
try:
os.link(self.unique_name, self.lock_file)
except OSError:
# Link creation failed. Maybe we've double-locked?
nlinks = os.stat(self.unique_name).st_nlink
if nlinks == 2:
# The original link plus the one I created == 2. We're
# good to go.
return
else:
# Otherwise the lock creation failed.
if timeout is not None and time.time() > end_time:
os.unlink(self.unique_name)
if timeout > 0:
raise LockTimeout("Timeout waiting to acquire"
" lock for %s" %
self.path)
else:
raise AlreadyLocked("%s is already locked" %
self.path)
time.sleep(timeout is not None and timeout/10 or 0.1)
else:
# Link creation succeeded. We're good to go.
return
def release(self):
if not self.is_locked():
raise NotLocked("%s is not locked" % self.path)
elif not os.path.exists(self.unique_name):
raise NotMyLock("%s is locked, but not by me" % self.path)
os.unlink(self.unique_name)
os.unlink(self.lock_file)
def is_locked(self):
return os.path.exists(self.lock_file)
def i_am_locking(self):
return (self.is_locked() and
os.path.exists(self.unique_name) and
os.stat(self.unique_name).st_nlink == 2)
def break_lock(self):
if os.path.exists(self.lock_file):
os.unlink(self.lock_file)
|