Windows shared lock with Python 3

[barry-gallagher]

In portalocker.py for SHARED locks the code has a sys.major version conditional that uses msvcrt flags on Python 3. The problem is that win32file.LockFileEx is being used so the flags don't match, and a non-blocking flag will block instead. Just remove the "if sys.version" and always use the win32con flags since msvcrt isn't used for SHARED.

[wolph]

Sorry for the really slow response, I didn't get an email about this issue.

I'm honestly a bit hesitant to change this behaviour at this point for 2 reasons:

1. I can't easily test the possible scenarios
2. It breaks backwards compatibility and some people might expect these results.

It does sound like a serious bug though... but I'm wondering if the better fix isn't to replace the win32file locking with msvcrt instead and remove win32file completely.

[barry-gallagher]

Unfortunately for me I ran into a Windows limit on the number of locked files and moved to a different solution. I understand your hesitance and leave it to your discretion as to how/if to change the code.

…

On Mon, Sep 13, 2021 at 10:07 PM Rick van Hattem ***@***.***> wrote: Sorry for the really slow response, I didn't get an email about this issue. I'm honestly a bit hesitant to change this behaviour at this point for 2 reasons: 1. I can't easily test the possible scenarios 2. It breaks backwards compatibility and some people might expect these results. It does sound like a serious bug though... but I'm wondering if the better fix isn't to replace the win32file locking with msvcrt instead and remove win32file completely. — You are receiving this because you authored the thread. Reply to this email directly, view it on GitHub <#64 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AFPX4Q7QJL7WT5GS6GHGVMTUB2U47ANCNFSM45CIXDUQ> . Triage notifications on the go with GitHub Mobile for iOS <https://apps.apple.com/app/apple-store/id1477376905?ct=notification-email&mt=8&pt=524675> or Android <https://play.google.com/store/apps/details?id=com.github.android&referrer=utm_campaign%3Dnotification-email%26utm_medium%3Demail%26utm_source%3Dgithub>.

[martin-eder-zeiss]

@wolph

Are there any updates about this? The shared lock feature is completely broken for me right now.

[wolph]

I've done some testing in the mean time and I believe the proposed solution is probably the best one. Even though it might break backwards compatibility in a few select cases.

I'll create a new release within the next few days

[wolph]

@martin-eder-zeiss Can you test the current develop branch? I think I've fixed it but I'm somewhat worried I might have broken something...

It seems to work flawlessly for me on a Windows machine though, but I might still be missing other test cases

[martin-eder-zeiss]

I am not familiar with Windows file locking mechanisms, but is it intended that this does not throw an AlreadyLocked exception?

portalocker.lock(file, portalocker.constants.LOCK_EX)
portalocker.lock(file, portalocker.constants.LOCK_SH | portalocker.constants.LOCK_NB)

How can I get a shared lock when there is already an exclusive one?

[wolph]

I tested it like this, and that seems to work as expected:

import portalocker


with portalocker.Lock('x', flags=portalocker.LOCK_EX):
    print('lock A')
    with portalocker.Lock('x', flags=portalocker.LOCK_SH | portalocker.LOCK_NB):
        print('lock B')

And I tried this as well:

import portalocker

with open('x', 'w') as a:
    portalocker.lock(a, portalocker.LOCK_EX)
    print('lock A')

    with open('x', 'w') as b:
        portalocker.lock(b, portalocker.LOCK_SH | portalocker.LOCK_NB)
        print('lock B')

Could it be that you reused the same file handle for both? So something like this:

import portalocker

with open('x', 'w') as a:
    portalocker.lock(a, portalocker.LOCK_EX)
    print('lock A')

    portalocker.lock(a, portalocker.LOCK_SH | portalocker.LOCK_NB)
    print('lock B')

[martin-eder-zeiss]

yep, I reused the file handle. Nevermind, everything seems to work now.

[egorvdot]

Hello @wolph. When the fix will be released?

[wolph]

Hello @wolph. When the fix will be released?

I've released version 2.5.0 about 3 weeks ago. Is it still broken for you?

[egorvdot]

Hello @wolph. When the fix will be released?

I've released version 2.5.0 about 3 weeks ago. Is it still broken for you?

Sorry, I got confused in my venv-s. I see updates in the latest release. Thanks!