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The possibility of using external libraries (that are loaded at runtime) has been available in C/C++ from the beginning, but in Fortran became only available in Fortran2003.  
The possibility of using external libraries (that are loaded at runtime) has been available in C/C++ for a long time, but in Fortran became only available as of Fortran2003.  


In the case of XDS, frame-reading and computation can be separated starting with version November-2016. This allows users/companies to develop their own specialized frame-reading libraries, and relieves the XDS maintainers from implementing even more file formats.
In the case of XDS, frame-reading and computation can be separated starting with version November-2016. This allows users/companies to develop their own specialized frame-reading libraries, and relieves the XDS maintainers from implementing even more file formats. The feature was developed in order to be able to natively (i.e. without temporary intermediates) read the HDF5 files written for data from the [[Eiger]] detector.


In the following, small examples are given for
In the following, small examples are given for
* how a program ("'''host'''") may use an existing external library, e.g. the dectris-neggia library ([https://github.com/dectris/neggia source]; [https://www.dectris.com/neggia.html#main_head_navigation pre-compiled])
* how a program ("'''host'''") may use an existing external library, e.g. the dectris-neggia library ([https://github.com/dectris/neggia source]; [https://www.dectris.com/company/news/newsroom/news-details/process-eiger-data-with-xds-fast pre-compiled])
* how an external library ("'''client'''") may be implemented that XDS can use
* how an external library ("'''client'''") may be implemented that XDS can use


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The interface was designed by Markus Mathes (Dectris), Vittorio Boccone (Dectris) and Kay Diederichs. It is supposed to be generic, i.e. useful beyond XDS. In particular, the 4096 bytes of the info_array can be utilized to obtain and use header information (e.g. wavelength, distance, axes specifications and other metadata).   
The interface was designed by Markus Mathes (Dectris), Vittorio Boccone (Dectris) and Kay Diederichs. It is supposed to be generic, i.e. useful beyond XDS. In particular, the 4096 bytes of the info_array can be utilized to obtain and use header information (e.g. wavelength, distance, axes specifications and other metadata).   
The interface has several [[LIB#Existing_implementations|implementations]].


== Host code example ==
== Host code example ==
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! ifort -qopenmp generic_data_plugin.f90 test_generic_host.f90 -o test_generic_host
! ifort -qopenmp generic_data_plugin.f90 test_generic_host.f90 -o test_generic_host
! or
! or
! gfortran -O -fopenmp -ldl generic_data_plugin.f90 test_generic.f90 -o test_generic_host
! gfortran -O -fopenmp -ldl generic_data_plugin.f90 test_generic_host.f90 -o test_generic_host
! run with  
! run with  
! ./test_generic_host < test.in
! ./test_generic_host < test.in
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! set some more module variables
! set some more module variables
     firstqm=INDEX(actnam,'?')
     firstqm=INDEX(actnam,'?')   ! qm means question mark
     lastqm =INDEX(actnam,'?',BACK=.TRUE.)
     lastqm =INDEX(actnam,'?',BACK=.TRUE.)
     len    =LEN_TRIM(actnam)
     len    =LEN_TRIM(actnam)
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MODULE plugin_test_mod
MODULE plugin_test_mod
       CHARACTER :: fn_template*132=''
       CHARACTER :: fn_template*132='',cformat*6='(i4.4)'
       INTEGER  :: lenfn,firstqm,lastqm
       INTEGER  :: lenfn,firstqm,lastqm
END MODULE
END MODULE
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       firstqm=INDEX(fn_template,'?')
       firstqm=INDEX(fn_template,'?')
       lastqm =INDEX(fn_template,'?',BACK=.TRUE.)
       lastqm =INDEX(fn_template,'?',BACK=.TRUE.)
      WRITE(cformat(3:5),'(i1,a1,i1)')lastqm-firstqm+1,'.',lastqm-firstqm+1
END SUBROUTINE plugin_open
END SUBROUTINE plugin_open
!
!
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! local variables
! local variables
     INTEGER k,i,dummy
     INTEGER k,i,dummy
     CHARACTER :: fn*132,cformat*6='(i4.4)'
     CHARACTER :: fn*132
     fn=fn_template
     fn=fn_template
    WRITE(cformat(3:5),'(i1,a1,i1)')lastqm-firstqm+1,'.',lastqm-firstqm+1
     IF (frame_number>0) WRITE(fn(firstqm:lastqm),cformat) frame_number
     IF (frame_number>0) WRITE(fn(firstqm:lastqm),cformat) frame_number
! -qopenmp compile option needs to be used otherwise race in writing fn
! -qopenmp compile option needs to be used otherwise race in writing fn
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! THE USE OR OTHER DEALINGS IN THE SOFTWARE.
! THE USE OR OTHER DEALINGS IN THE SOFTWARE.
!
!
! For more information, please refer to For more information, please refer to <http://unlicense.org/>
! For more information, please refer to <http://unlicense.org/>
!
!
!
!
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</pre>
</pre>
Google returns https://github.com/apple/cups/issues/4410 and https://bugzilla.redhat.com/show_bug.cgi?id=1065695 when searching for similar problems. Overall, this appears to be harmless and in fact I don't know how to change the code to make the segfault disappear  - I'd appreciate a patch!
Google returns https://github.com/apple/cups/issues/4410 and https://bugzilla.redhat.com/show_bug.cgi?id=1065695 when searching for similar problems. Overall, this appears to be harmless and in fact I don't know how to change the code to make the segfault disappear  - I'd appreciate a patch!
== Existing implementations ==
# [https://github.com/dectris/neggia Dectris Neggia-plugin] to read HDF5 written by Dectris-supplied software of Eiger detectors
# [https://github.com/DiamondLightSource/durin Diamond's Durin-plugin] to read HDF5 written by Eiger detectors at Diamond (and presumably elsewhere); latest binaries for MacOS and Linux (RHEL6) as well as example XDS.INP and source at https://github.com/DiamondLightSource/durin/releases/latest
# [https://git.embl.de/nikolova/xds-zcbf/ EMBL-Hamburg's zcbf-plugin] to read gzip-compressed CBF files without intermediate file
== See also ==
# https://rosettacode.org/wiki/Call_a_function_in_a_shared_library#GNU_Fortran_on_Linux
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