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Commit cf57a3a7 authored by Alan De Smet's avatar Alan De Smet
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Cleaning up exclusivelockfile

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csppfetch/exclusivelockfile.py
+ 52
− 124
View file @ cf57a3a7
......@@ -6,20 +6,56 @@ import logging
class ExclusiveLockFile:
""" Lock a file by name or handle, returning an open file handle
Intended to be used in a "with" block as a context manager.
Can be used in a "with" block as a context manager.
>>> import tempfile
>>> with tempfile.TemporaryDirectory() as dir:
... lockfile = dir+"/lock"
... open(lockfile,"w").close()
... with ExclusiveLockFile(lockfile) as f:
... # Can assume exclusive control of lockfile
... # Can use f as a file object
... pass
... f = open(lockfile,"w")
... with ExclusiveLockFile(f):
... # Can assume exclusive control of lockfile
... pass
>>> from exclusivelockfile import ExclusiveLockFile
>>> from tempfile import mkdtemp
>>> tmpdir = mkdtemp()
>>> filename = tmpdir+"/lock"
>>>
>>> # You can't lock a file until it exists
>>>
>>> ExclusiveLockFile(filename) # doctest: +ELLIPSIS
Traceback (most recent call last):
...
FileNotFoundError: [Errno 2] No such file or directory: '.../lock'
>>>
>>> # You can lock a file-like object that support f.name and fcntl.lockf(f)
>>>
>>> f = open(filename,"w")
>>> with ExclusiveLockFile(f):
... # Can assume exclusive control of filename
... pass
>>> f.close()
>>>
>>> # You can lock an existing file by name (str, bytes, or Path-like object).
>>>
>>> with ExclusiveLockFile(filename) as f:
... # Can assume exclusive control of filename
... # Can use f as a file object
... pass
>>>
>>> # Also supports manual use; you MUST call unlock in this case!
>>>
>>> l = ExclusiveLockFile(filename)
>>> l.lock()
>>> # Can assume exclusive control of filename
>>> l.unlock()
>>>
>>> # Error cases
>>> l.unlock() # doctest: +ELLIPSIS
Traceback (most recent call last):
...
RuntimeError: Attempting to unlock .../lock, but I don't have that lock
>>> l.lock()
>>> l.lock() # doctest: +ELLIPSIS
Traceback (most recent call last):
...
RuntimeError: Attempting to lock .../lock, but I already have that lock
>>>
>>> import os
>>> os.unlink(filename)
>>> os.rmdir(tmpdir)
"""
def __init__(self, filename_or_file):
......@@ -31,56 +67,7 @@ class ExclusiveLockFile:
file-like objects will only work to the extent that
fcntl.lockf works on them.
>>> from exclusivelockfile import ExclusiveLockFile
>>> from tempfile import mkdtemp
>>> tmpdir = mkdtemp()
>>> filename = tmpdir+"/lock"
>>>
>>> # You can't lock a file until it exists
>>>
>>> ExclusiveLockFile(filename) # doctest: +ELLIPSIS
Traceback (most recent call last):
...
FileNotFoundError: [Errno 2] No such file or directory: '.../lock'
>>>
>>> # You can lock a file-like object that support f.name and fcntl.lockf(f)
>>>
>>> f = open(filename,"w")
>>> with ExclusiveLockFile(f):
... # Can assume exclusive control of filename
... pass
>>> f.close()
>>>
>>> # You can lock an existing file by name (str, bytes, or Path-like object).
>>>
>>> with ExclusiveLockFile(filename) as f:
... # Can assume exclusive control of filename
... # Can use f as a file object
... pass
>>>
>>> # Also supports manual use; you MUST call unlock in this case!
>>>
>>> l = ExclusiveLockFile(filename)
>>> l.lock()
>>> # Can assume exclusive control of filename
>>> l.unlock()
>>>
>>> # Error cases
>>> l.unlock() # doctest: +ELLIPSIS
Traceback (most recent call last):
...
RuntimeError: Attempting to unlock .../lock, but I don't have that lock
>>> l.lock()
>>> l.lock() # doctest: +ELLIPSIS
Traceback (most recent call last):
...
RuntimeError: Attempting to lock .../lock, but I already have that lock
>>>
>>> import os
>>> os.unlink(filename)
>>> os.rmdir(tmpdir)
Extended examples are in help(exclusivelockfile.ExclusiveLockFile)
"""
try:
# Ensure it's Path-like
......@@ -88,7 +75,7 @@ class ExclusiveLockFile:
self.file = None
self.filename = filename_or_file
except:
# Hopefully it's file-like
# Not Path-like? I hope it's file-like
self.file = filename_or_file
self.filename = None
......@@ -202,7 +189,7 @@ def file_matches_filename(file, filename):
return False
class AtomicCreateIfMissing:
""" Context manager to atomically crate a file
""" Context manager to atomically create a file
>>> from exclusivelockfile import AtomicCreateIfMissing
>>> from tempfile import mkdtemp
......@@ -264,62 +251,3 @@ class AtomicCreateIfMissing:
os.rename(self.lockfilename, self.filename)
self.lock.unlock()
if False:
class ExclusiveLockFileOLD:
""" Lock a temporary file created for the purpose.
Intended to be used in a "with" block as a context manager.
The file will be created if it doesn't exist. It will be deleted when the
block exits! The filename should not be a directory.
If multiple processes try to lock the same file, the first to succeed will
delete it when done. That means that a process starting after that point
will create _new_ file and lock that, not sharing the previous one! This
makes it only suitable for VERY specialized purposes (like ensuring only
one process downloads a file, and later processes will immediately bail out
if the downloaded file is already preent).
Be warned that this is implemented using fcntl.lockf which is an ADVISORY
lock; only code using fcntl.lockf or similar will resepect it.
WILL create missing directories if necessary, will NOT
remove them on completion.
>>> import tempfile
>>> with tempfile.TemporaryDirectory() as dir:
... with ExclusiveLockFile(dir+"/lock"):
... # In this block, the file f.name is exclusively locked
... # using fcntl.lockf. (Only code using fcntl.lockf or
... # equivalent will respect this!)
... pass
"""
def __init__(self, filename):
self.filename = filename
def lock(self):
dir = os.path.dirname(self.filename)
if len(dir) and not os.path.exists(dir):
logging.debug("directory {} does not exist to hold lockfile {}; creating".format(dir, self.filename))
os.makedirs(dir)
logging.debug("Attempting to lock {0}".format(self.filename))
self.f = open(self.filename, "w")
fcntl.lockf(self.f, fcntl.LOCK_EX)
logging.debug("Locked {0}".format(self.filename))
def unlock(self):
fcntl.lockf(self.f, fcntl.LOCK_UN)
self.f.close()
try:
os.unlink(self.filename)
except FileNotFoundError:
# another lock erased me; we're okay with that
pass
logging.debug("unlocked {0}".format(self.filename))
def __enter__(self):
self.lock()
def __exit__(self, type, value, traceback):
self.unlock()
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