[Scons-users] Timing Issue with files retrieved from the SCons Cache

Fri Sep 30 14:11:54 EDT 2016

Shane,

Since this is a race condition, then that is expected. SCons 2.5.0 was a
major feature release. It added support for cross-language dependencies
which would affect timings on how long files may be open.

V/R,
William

On Fri, Sep 30, 2016 at 1:56 PM, Shane Gannon <sgannon200 at gmail.com> wrote:

> Hi William
>
> Sounds like this issue could be related. But I think SCons 2.5.0 may be
> playing it's part. The 2.3.4 build we have does not hit this problem.
> Well... at least not with the same level of consistency.
>
> Regards
> Shane
>
> On Fri, Sep 30, 2016 at 5:55 PM, William Blevins <wblevins001 at gmail.com>
> wrote:
>
>> Shane,
>>
>> This may be specific to Python file handling on Windows and not specific
>> to SCons 2.5.0. The mail archive is down currently, so I cannot link to the
>> full article, but here is an excerpt from one of the last conversations.
>>
>>
>> Hi All -
>>>
>>
>>> Our resident Windows expert reached the following conclusions:
>>>
>>> Summary: It is a python bug in shutil.copy2
>>>
>>> The issue:
>>> When link.exe opens a obj file, it gets the following error:
>>> LINK : fatal error LNK1104: cannot open file
>>> 'build\cached\mongo\tools\mongobridge_options_init.obj'
>>>
>>> To diagnose these errors, I enabled ETW tracing with "FileIO stackwalk
>>> for FileCreate
>>> <https://msdn.microsoft.com/en-us/library/windows/desktop/aa964768%28v=vs.85%29.aspx>
>>> +FileCleanup+FileClose"
>>> <https://msdn.microsoft.com/en-us/library/windows/desktop/aa964773%28v=vs.85%29.aspx> and
>>> cranked through WPA with the data on Window 2008 R2 & Window 2012 R2. The
>>> 2012 R2 os offers stack traces which is why I used it
>>>
>>> By tracing the build, I can see that link.exe has a call to CreateFile
>>> fail with
>>> "A file cannot be opened because the share access flags are
>>> incompatible. (0xc0000043)"
>>>
>>> This occurs because it asked for a file with the following flags "file_open
>>> synchronous_io_nonalert non_directory_file shareRead", and another
>>> process had an existing handle to the file"file_overwrite_if
>>> synchronous_io_nonalert non_directory_file normal shareRead shareWrite".
>>>
>>> The existing process that had a handle to the file was none other then
>>> "python.exe" which created the file originally in copy2, but did not close
>>> it. I compared normal cases, and it does succesfully close the file. I do
>>> not know why like 1/100 or 1/200 times it fails.
>>>
>>> The workaround is win32file.CopyFile
>>> <http://timgolden.me.uk/python/win32_how_do_i/copy-a-file.html>.
>>>
>>> I patched FS.py with and it worked fine
>>> win32file.CopyFile(src, dst, 1)
>>>         return True
>>>
>>>
>>> I can confirm that the issue no-longer reproduces for me with the
>>> following change to FS.py:
>>>
>>> https://github.com/tychoish/mongo/commit/c8450fb4d304b2de06b
>>> a968b71f6efacd3b5214e
>>>
>>> While I'd love to follow this deeper, debugging python's file system
>>> internals on Windows is not something I can really invest time in right
>>> now. We are most likely just going to make the above patch to our vendored
>>> copy of SCons and continue.
>>>
>>> Perhaps someone with more Python expertise would be interested in
>>> pursuing this further? I can give very detailed reproduction instructions.
>>>
>>> Thanks,
>>> Andrew
>>>
>>
>> I do not think this has been officially patched in the development trunk
>> yet, but it is a known issue.
>>
>> V/R,
>> William
>>
>>
>> On Fri, Sep 30, 2016 at 12:16 PM, Shane Gannon <sgannon200 at gmail.com>
>> wrote:
>>
>>> Hi
>>>
>>> I'm hitting a problem with the SCons Cache. Intermiddently (but too
>>> frequently) a build fails with an error like
>>>
>>> *Elapsed Time*
>>>
>>> *00:06:43.214* scons: building `out\windows-x86-MD-unicode-vs2015-rel\obj-static\components\memorymanager\tests\unit_tests\TestMemoryManager.obj' because it doesn't exist*00:06:43.215* Retrieved `out\windows-x86-MD-unicode-vs2015-rel\obj-static\components\memorymanager\tests\unit_tests\TestMemoryManager.obj' from cache
>>>
>>>
>>> *00:06:45.660* scons: building `src\jabber-client\jabber-build\Win32\bin\Release\memorymanager-unit-tests.exe' because it doesn't exist*00:06:45.661* LINK src\jabber-client\jabber-build\Win32\bin\Release\memorymanager-unit-tests.exe
>>>
>>> *00:06:45.694* LINK : fatal error LNK1104: cannot open file 'out\windows-x86-MD-unicode-vs2015-rel\obj-static\components\memorymanager\tests\unit_tests\TestMemoryManager.obj'
>>>
>>>
>>> It's not specific to .obj files. It can happen for generated .h files,
>>> .libs, etc. Basically any file retrievable from the cache.
>>>
>>> This only occurs on a new build we're working to support. Namely an
>>> upgrade to Visual Studio 2015 where SCons 2.5.0 is used (versus 2.3.4 on
>>> the other machines).
>>>
>>> I noticed in the Release Notes the following entries for 2.5.0.
>>>
>>>     - SCons handles cache directories a bit differently/
>>>       - Cache files are now stored in 256 subdirectories in the cache directory by
>>>         default (this stresses NFS less). Existing cache directories will remain as
>>>         current, but SCons will prompt you to run scons-configure-cache which will
>>>         allow you to migrate to the new layout, or confirm you want to use the
>>>         existing layout.
>>>
>>>     - New external tool scons-configurecache which allows some configuration of
>>>       how files in the cache are controlled.
>>>
>>> I assume this might be causing the problem. Has anyone else reported an
>>> issue?
>>>
>>> Does anyone have a suggestion on how I can resolve or diagnois it?
>>>
>>> PS: We use Windows 10 on our build machines.
>>>
>>> Regards
>>> Shane
>>>
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>>> Scons-users at scons.org
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>>>
>>>
>>
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