CALL_EXTERNAL problems (re: DICOM)

["Richard Tyc" <richt(at)sbrc.umanitoba.ca>]

This may interest anyone who is using IDL with DICOM SCP servers.

I am trying to use CALL_EXTERNAL to initate a DICOM query and retrieve a
list of patients and/or studies from a PACS  archive acting as a Query SCP.

I am using the CTN test code (Ansi C) from Mallinkrodt Institute of
Radiology (MIR).
Essentially, I have modified the query_client application (which was a motif
application) and turned it into a shared library.  This involved removing
all of the X windows stuff and turning the callbacks from widgets into C
finctions I can call from IDL.  I was successfully querying a dicom server
running on the same machine as IDL and getting patient lists, etc.

When I took the machine down to our MRI lab, I cannot get patient lists from
IDL although the original query_client works.  The main difference is now
the CTN test code is querying across the net to the MRI system.  The way a
dicom query works is that first an association is made (which works!) and
then for each response from the server a callback function is called which
extracts the query data (all taking place over TCP/IP).  Now all this takes
place in the linked in librarie(s) which IDL calls.  To make this work in
IDL , I simply ensured all of the libraries linked in were shared libs.
Note, the library created with the IDL function calls links with many other
utilites providing the DICOM services.

Does anyone see any problem with this ?  It seems to provide no query
responses at all from the server.  In order for this to happen, the C code
must fundamentally  be accepting sockets and waiting on socket reads to
acquire data all during one IDL CALL_EXTERNAL.  When the system was working
on a standalone machine, it seems to indicate that success is dependent on
no delays in the socket stuff.  When I moved the app to network wide queries
with inherent delays, I simply get no query data returned from the DICOM
server.  Do I have to do anything special in the other C libs not directly
called by IDL but are linked in.

I am running IDL 5.2.1 on SGI 6.5 compiling with -n32 binaries.

Thanks
Rich