文件锁未按预期工作
我有一个 Thread 扩展类，它应该一次只运行一个实例（跨进程）。为了实现这一点，我尝试使用文件锁。以下是我的代码片段：
class Scanner(Thread):
def __init__(self, path):
Thread.__init__(self)
self.lock_file = open(os.path.join(config.BASEDIR, "scanner.lock"), 'r+')
fcntl.lockf(self.lock_file, fcntl.LOCK_EX | fcntl.LOCK_NB)
# Stuff omitted
def run(self):
logging.info("Starting scan on %s" % self.path)
# More stuff omitted
fcntl.lockf(self.lock_file, fcntl.LOCK_UN)
如果 Scanner 线程已经在运行并且根本不初始化对象，我预计 lockf 调用会抛出异常。但是，我可以在终端中看到这一点：
INFO:root:Starting scan on /home/felix/Music
INFO:root:Starting scan on /home/felix/Music
INFO:root:Scan finished
INFO:root:Scan finished
这表明两个 Scanner 线程同时运行，没有抛出异常。我确信我在这里遗漏了一些非常基本的东西，但我似乎无法弄清楚那是什么。有人可以帮忙吗？
I have a Thread-extending class that is supposed to run only one instance at a time (cross-process). In order to achieve that, I'm trying to use a file lock. Here are bits of my code:
class Scanner(Thread):
def __init__(self, path):
Thread.__init__(self)
self.lock_file = open(os.path.join(config.BASEDIR, "scanner.lock"), 'r+')
fcntl.lockf(self.lock_file, fcntl.LOCK_EX | fcntl.LOCK_NB)
# Stuff omitted
def run(self):
logging.info("Starting scan on %s" % self.path)
# More stuff omitted
fcntl.lockf(self.lock_file, fcntl.LOCK_UN)
I was expecting the lockf call to throw an exception if a Scanner thread was already running and not initialize the object at all. However, I can see this in the terminal:
INFO:root:Starting scan on /home/felix/Music
INFO:root:Starting scan on /home/felix/Music
INFO:root:Scan finished
INFO:root:Scan finished
Which suggests that two Scanner threads are running at the same time, no exception thrown. I'm sure I'm missing something really basic here, but I can't seem to figure out what that is. Can anyone help?
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最后我自己找到了解决方案。它是使用
fcntl.flock()而不是fcntl.lockf()，具有完全相同的参数。不知道为什么这会产生影响。Found the solution myself in the end. It was to use
fcntl.flock()instead offcntl.lockf(), with the exact same parameters. Not sure why that made a difference.您正在使用
r+打开锁定文件，这会擦除以前的文件并创建一个新文件。每个线程都锁定不同的文件。使用
w或r+aYou're opening the lock file using
r+which is erasing the previous file and creating a new one. Each thread is locking a different file.Use
worr+a除了使用集群之外，我还必须像这样打开文件：
否则它不起作用。
Along with using flock, I had to also open the file like so :
It does not work other wise.