我需要锁定一个文件写在Python。它将被多个Python进程同时访问。我在网上找到了一些解决方案,但大多数都无法达到我的目的,因为它们通常只是基于Unix或Windows的。


当前回答

锁定是平台和设备特定的,但一般来说,你有几个选择:

Use flock(), or equivalent (if your os supports it). This is advisory locking, unless you check for the lock, it's ignored. Use a lock-copy-move-unlock methodology, where you copy the file, write the new data, then move it (move, not copy - move is an atomic operation in Linux -- check your OS), and you check for the existence of the lock file. Use a directory as a "lock". This is necessary if you're writing to NFS, since NFS doesn't support flock(). There's also the possibility of using shared memory between the processes, but I've never tried that; it's very OS-specific.

对于所有这些方法,您必须使用自旋锁(失败后重试)技术来获取和测试锁。这确实为错误同步留下了一个小窗口,但它通常小到不会成为一个大问题。

如果您正在寻找跨平台的解决方案,那么您最好通过其他机制将日志记录到另一个系统(其次是上面的NFS技术)。

请注意,sqlite在NFS上受到与普通文件相同的约束,因此您不能在网络共享上写入sqlite数据库并免费获得同步。

其他回答

场景是这样的: 用户请求一个文件执行某些操作。然后,如果用户再次发送相同的请求,它会通知用户在第一个请求完成之前不会完成第二个请求。这就是为什么我使用锁定机制来处理这个问题。

下面是我的工作代码:

from lockfile import LockFile
lock = LockFile(lock_file_path)
status = ""
if not lock.is_locked():
    lock.acquire()
    status = lock.path + ' is locked.'
    print status
else:
    status = lock.path + " is already locked."
    print status

return status

锁定是平台和设备特定的,但一般来说,你有几个选择:

Use flock(), or equivalent (if your os supports it). This is advisory locking, unless you check for the lock, it's ignored. Use a lock-copy-move-unlock methodology, where you copy the file, write the new data, then move it (move, not copy - move is an atomic operation in Linux -- check your OS), and you check for the existence of the lock file. Use a directory as a "lock". This is necessary if you're writing to NFS, since NFS doesn't support flock(). There's also the possibility of using shared memory between the processes, but I've never tried that; it's very OS-specific.

对于所有这些方法,您必须使用自旋锁(失败后重试)技术来获取和测试锁。这确实为错误同步留下了一个小窗口,但它通常小到不会成为一个大问题。

如果您正在寻找跨平台的解决方案,那么您最好通过其他机制将日志记录到另一个系统(其次是上面的NFS技术)。

请注意,sqlite在NFS上受到与普通文件相同的约束,因此您不能在网络共享上写入sqlite数据库并免费获得同步。

我更喜欢lockfile——平台独立的文件锁定

你会发现pylocker很有用。它可以用于锁定文件或一般的锁定机制,并且可以从多个Python进程一次访问。

如果你只是想锁定一个文件,下面是它的工作原理:

import uuid
from pylocker import Locker

#  create a unique lock pass. This can be any string.
lpass = str(uuid.uuid1())

# create locker instance.
FL = Locker(filePath='myfile.txt', lockPass=lpass, mode='w')

# aquire the lock
with FL as r:
    # get the result
    acquired, code, fd  = r

    # check if aquired.
    if fd is not None:
        print fd
        fd.write("I have succesfuly aquired the lock !")

# no need to release anything or to close the file descriptor, 
# with statement takes care of that. let's print fd and verify that.
print fd

这里有一个跨平台的文件锁定模块:Portalocker

尽管正如Kevin所说,从多个进程同时写入文件是您希望尽可能避免的事情。

如果可以将问题硬塞到数据库中,则可以使用SQLite。它支持并发访问并处理自己的锁定。