linklockfile.py 文件源码

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 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 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