look for the last writing time. I’m gonna do that.
···
On 19.07.2015 18:52, Werner Benger
wrote:
Hi Samer,
it would look easier to me to just check the last write time,
under windows this is function GetFileTime:
under Linux, stat() should do. Building an md5 hash seems like a
slower version, but both couldn’t catch
the case where an application opens a file, writes data, close it,
opens the file again, adds more data,
closes it again… but neither would the locking mechanism or the
file handle approach help in that case.
So maybe checking the file write time would be best. At first you
could measure how frequently a file
is modified, e.g. you find out every minute. Then if you measure
that the file has not been modified for
10 minutes, it’s assumed the file will no longer be modified. It
wouldn’t catch the case that an application
is writing data to the file and they still remain in write cache
with the file being kept open but the application
is doing something different for a while. However, it seems it
requires some kind of “guessing” anyway what
the writing application is doing, especially if it would
repeatedly close and re-open the same file to append data.
Cheers,
����� Werner
https://msdn.microsoft.com/en-us/library/windows/desktop/ms724320%28v=vs.85%29.aspx
On 19.07.2015 16:47, Samer Afach
wrote:
Dear Werner:
Thanks for the suggestions. I'll keep these suggestions as last
resort because my program is cross-platform, so I’m trying to
avoid such low-level functions.
I'm thinking now of using an md5 hash of the file instead of the
size. Do you think that would suffice and work? The only problem
with that is that it could be a little expensive, but that’s
still OK if that’s the only problem because the files aren’t
really that big (a few megabytes).
All the best,
Samer
On 19.07.2015 16:37, Werner Benger
wrote:
Hi Samer,
�if those applications are linking dynamically with HDF5, you
could interface there by providing a “patched” version of HDF5
that is binary compatible, but still performs some file
locking, possibly via a modified VFD.
Just checking the file sizes won't be a sure check, in
particular it would not work for and application that does not
append data but modifies existing ones. You should be able to
check the “last modified” date on the file as well, and if the
HDF5 file cannot be opened by another application, then it’s
either corrupted or still open and data written to it.
It should also be possible to find out which process has file
handles to a specific file open, both Linux and Windows seem
to allow that, just in an OS-specific way:
It may require your program to run under admin rights though.
Cheers,
��������� Werner
http://stackoverflow.com/questions/6583158/finding-open-file-descriptors-for-a-process-linux-c-code
https://technet.microsoft.com/en-us/sysinternals/bb896653.aspx
On 19.07.2015 12:32, Samer Afach
wrote:
Dear Werner:
Unfortunately I don't have the source of the writing
program. It could be anything actually; labview, C, C++,
etc… . I’m working on a collaborative program for
collecting data, and my software is supposed to upload the
data to the main storage server for backup and data
analysis. Everyone is free to use any tools they want for
data acquisition.
Is there any solution to my problem that doesn't involve me
having authority on the writing program? Currently I’m using
a method that I invented, where I measure the size of the
file multiple times, and if the size doesn’t change for some
time, then that decide that the file isn’t being written…
that’s the only way I could come up with, but this has
nothing to do with HDF5.
All the best,
Samer
On 19.07.2015 12:23, Werner
Benger wrote:
Hi Samer,
�do you have full source code access to both programs, the
one writing the file and the one uploading it?
If so, would adding some file locking mechanism (� ) help your case?
Cheers,
������������� Werner
https://en.wikipedia.org/wiki/File_locking
On 19.07.2015 02:50, Samer
Afach wrote:
Dear Werner:
Thank you for your response and your time.
I tried modifying the source code of h5check, but it's
very complicated and returns strings instead of error
codes. Besides, I tried to compile it by including the
three files in the main c file and it gave errors that
don’t seem to be easily trackable. It’ll take me lots of
time to prepare something reliable out of it with full
testing. I wonder why the hdf group didn’t implement
such a functionality in low language, I thought it
exists and I can’t find it. 
About my second question, apparently I wasn't clear on
what I really need and I was misunderstood. What I need
is to check whether the file I want to read is being
accessed by some other program. My problem is that the
file I wanna deal with is being written by some other
program, and I want to initiate an upload after it’s
done writing. So I would like to check whether the other
program is finished writing and closed it before I send
it to my upload queue.
All the best,
Samer
On 18.07.2015 23:11, Werner
Benger wrote:
Hi Samer,
Is there any objection against you taking the source
code of h5check, rename the main function to
h5check_main() and then call it as C function from
your code?
This sounds as if you want to know what the HDF5
library is currently doing with a file? Well what you
could do is to modify the virtual file driver that you
want to use, and let it keep track of that happens
with the file. It’s the VFD that does the actual
writing of a file content, so you can trace its
write() call to keep track what exactly happens when.
It’s some effort of course.
Cheers,
���������� Werner
On 18.07.2015 16:23,
Samer Afach wrote:
Dear pros:
I have two similar issues I would like to ask about,
and I’d be grateful if you could help me:
1- How can I check HDF5 file integrity in C/C++ (I
prefer low level C)? I know there’s a software
called h5check, but I need a function to do that,
not a software. In my application, it’s not an
option to execute h5check from my system.
2- How can I do a quick check in C/C++
to see whether the file is being
written/modified/open for write? I looked [
in
this link](https://www.hdfgroup.org/HDF5/doc/H5.format.html#FileMetaData) which discusses metadata, but there
doesn’t seem to be a clear way through the C/C++
interface for me a to read the first two bits that
give me that information. Could you please help with
that with a simple example?
All the best,
Samer
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-- ___________________________________________________________________________
Dr. Werner Benger Visualization Research
Center for Computation & Technology at Louisiana State University (CCT/LSU)
2019 Digital Media Center, Baton Rouge, Louisiana 70803
Tel.: +1 225 578 4809 Fax.: +1 225 578-5362
_______________________________________________
Hdf-forum is for HDF software users discussion.
Twitter:
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_______________________________________________
Hdf-forum is for HDF software users discussion.
Twitter:
Hdf-forum@lists.hdfgroup.orghttp://lists.hdfgroup.org/mailman/listinfo/hdf-forum_lists.hdfgroup.orghttps://twitter.com/hdf5
-- ___________________________________________________________________________
Dr. Werner Benger Visualization Research
Center for Computation & Technology at Louisiana State University (CCT/LSU)
2019 Digital Media Center, Baton Rouge, Louisiana 70803
Tel.: +1 225 578 4809 Fax.: +1 225 578-5362
_______________________________________________
Hdf-forum is for HDF software users discussion.
Twitter:
Hdf-forum@lists.hdfgroup.orghttp://lists.hdfgroup.org/mailman/listinfo/hdf-forum_lists.hdfgroup.orghttps://twitter.com/hdf5
_______________________________________________
Hdf-forum is for HDF software users discussion.
Twitter:
Hdf-forum@lists.hdfgroup.orghttp://lists.hdfgroup.org/mailman/listinfo/hdf-forum_lists.hdfgroup.orghttps://twitter.com/hdf5
-- ___________________________________________________________________________
Dr. Werner Benger Visualization Research
Center for Computation & Technology at Louisiana State University (CCT/LSU)
2019 Digital Media Center, Baton Rouge, Louisiana 70803
Tel.: +1 225 578 4809 Fax.: +1 225 578-5362
_______________________________________________
Hdf-forum is for HDF software users discussion.
Twitter:
Hdf-forum@lists.hdfgroup.orghttp://lists.hdfgroup.org/mailman/listinfo/hdf-forum_lists.hdfgroup.orghttps://twitter.com/hdf5
_______________________________________________
Hdf-forum is for HDF software users discussion.
Twitter:
Hdf-forum@lists.hdfgroup.orghttp://lists.hdfgroup.org/mailman/listinfo/hdf-forum_lists.hdfgroup.orghttps://twitter.com/hdf5
-- ___________________________________________________________________________
Dr. Werner Benger Visualization Research
Center for Computation & Technology at Louisiana State University (CCT/LSU)
2019 Digital Media Center, Baton Rouge, Louisiana 70803
Tel.: +1 225 578 4809 Fax.: +1 225 578-5362
_______________________________________________
Hdf-forum is for HDF software users discussion.
Twitter:
Hdf-forum@lists.hdfgroup.orghttp://lists.hdfgroup.org/mailman/listinfo/hdf-forum_lists.hdfgroup.orghttps://twitter.com/hdf5
