In some cases, QLockFile::lock() may not block, nor will the lock succeed. For example: the disk space is full, the user lacks permissions on the directory, etc.
For example: When the disk space is full, there are two threads accessing, the first thread will cause the mutex to be locked, QFileLock::lock() will not block, nor will it be successfully locked. At this point the second thread will be blocked because the mutex is not unlocked
Signed-off-by: Shoucheng Zhang email@example.com