Portalocker没有按预期退出，而fcntl会退出

Question

我不明白为什么portalocker没有优雅地失败，并显示消息"有一个锁定文件"。相反，它会失败并显示以下错误：

portalocker.exceptions.LockException: [Errno 11] Resource temporarily unavailable

请注意，这个问题已经被问过了，但没有人令人信服地回答。 参见 python-lock-a-file这是有问题的脚本，必须在两个不同的控制台中启动。

#!/usr/bin/python3
import portalocker
import sys
def open_and_lock(full_filename):
    file_handle = open(full_filename, 'w')
    try:
        portalocker.lock(file_handle, portalocker.LOCK_EX | portalocker.LOCK_NB)
        return file_handle
    except IOError:
        print ("there is a lockfile")
        sys.exit(-1)
# positioning a lock
lock_name = 'my_lock'
fh = open_and_lock(lock_name)
# do something consumer in time
i = 0
while (i < 100000000):
    i += 1
    print ("i :", i)
# lock release
close(fh)

将便携式设备替换为 fcntl 和 ...一切正常！

#!/usr/bin/python3
import fcntl
import sys
def open_and_lock(full_filename):
    file_handle = open(full_filename, 'w')
    try:
        fcntl.lockf(file_handle, fcntl.LOCK_EX | fcntl.LOCK_NB)
        return file_handle
    except IOError:
        print ("there is a lockfile")
        sys.exit(-1)
# positioning a lock
lock_name = 'my_lock'
fh = open_and_lock(lock_name)
# do something consumer in time
i = 0
while (i < 100000000):
    i += 1
    print ("i :", i)
# lock release
close(fh)

这是怎么回事？为什么portalocker和fcntl之间的行为存在差异？

附言：蟒蛇 3.6.7乌班图 18.04

Answer 1

例外是一个优雅的例外：portalocker.exceptions.LockException

与直接使用 fcntl 相反，portalocker包装异常，使其在多个平台上工作。fcntl示例不适用于Windows，portalocker:)

测试显示了一些有用的示例： https://github.com/WoLpH/portalocker/blob/develop/portalocker_tests/tests.py

在您的情况下，与其捕获IOError，不如捕获portalocker.exceptions.LockException。此外，您也应该始终正确解锁，因此我建议以下内容：

#!/usr/bin/python3
import portalocker
import sys

# positioning a lock
lock_name = 'my_lock'
try:
    with portalocker.Lock(lock_name, portalocker.LOCK_EX | portalocker.LOCK_NB):
        # do something consumer in time
        i = 0
        while (i < 100000000):
            i += 1
            print ("i :", i)
except portalocker.exceptions.LockException:
    print ("there is a lockfile")
    sys.exit(-1)

或者，如果您确实想要显式锁定和解锁：

#!/usr/bin/python3
import portalocker
import sys
def open_and_lock(full_filename):
    file_handle = open(full_filename, 'w')
    try:
        portalocker.lock(file_handle, portalocker.LOCK_EX | portalocker.LOCK_NB)
        return file_handle
    except portalocker.exceptions.LockException:
        print ("there is a lockfile")
        sys.exit(-1)
# positioning a lock
lock_name = 'my_lock'
fh = open_and_lock(lock_name)
try:
    # do something consumer in time
    i = 0
    while (i < 100000000):
        i += 1
        print ("i :", i)
finally:
    # lock release
    portalocker.unlock(fh)