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from __future__ import absolute_import
import time
import os
from . import (LockBase, LockFailed, NotLocked, NotMyLock, LockTimeout,
AlreadyLocked)
class SymlinkLockFile(LockBase):
"""Lock access to a file using symlink(2)."""
def __init__(self, path, threaded=True, timeout=None):
# super(SymlinkLockFile).__init(...)
LockBase.__init__(self, path, threaded, timeout)
# split it back!
self.unique_name = os.path.split(self.unique_name)[1]
def acquire(self, timeout=None):
# Hopefully unnecessary for symlink.
#try:
# open(self.unique_name, "wb").close()
#except IOError:
# raise LockFailed("failed to create %s" % self.unique_name)
timeout = timeout if timeout is not None else self.timeout
end_time = time.time()
if timeout is not None and timeout > 0:
end_time += timeout
while True:
# Try and create a symbolic link to it.
try:
os.symlink(self.unique_name, self.lock_file)
except OSError:
# Link creation failed. Maybe we've double-locked?
if self.i_am_locking():
# Linked to out unique name. Proceed.
return
else:
# Otherwise the lock creation failed.
if timeout is not None and time.time() > end_time:
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/10 if timeout is not None else 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 self.i_am_locking():
raise NotMyLock("%s is locked, but not by me" % self.path)
os.unlink(self.lock_file)
def is_locked(self):
return os.path.islink(self.lock_file)
def i_am_locking(self):
return os.path.islink(self.lock_file) and \
os.readlink(self.lock_file) == self.unique_name
def break_lock(self):
if os.path.islink(self.lock_file): # exists && link
os.unlink(self.lock_file)