Experimental Physics and
Industrial Control System

Benjamin Franksen <[email protected]> · Thu, 19 Dec 2013 22:30:42 +0100

Am Donnerstag, 19. Dezember 2013, 12:40:52 schrieb Andrew Johnson:
> On 12/19/2013 11:40 AM, Mark Rivers wrote:
> [...] if
> seq-2.1.15 has added the variable to a header file that declaration must
> be marked with epicsShareExtern which on Windows expands to either
> 
> #define epicsShareExtern __declspec(dllexport) extern
> 
> or
> 
> #define epicsShareExtern __declspec(dllimport) extern
> 
> depending on whether the header is being included by a file that will be
> part of the same DLL as seq_if.c or must be imported from that DLL.
> 
> I guess Ben's issue might be that he has no header file declaring this
> variable, so the compiler never gets told whether it's going to be an
> import or an export. The solution should thus be to add a suitably
> decorated declaration of the variable to an appropriate header file.

Hi Andrew

thanks for your input. I intentionally did not declare the variable in a 
header file because it is a crude hack I added for the tests and was never 
meant for public consumption.

Peter Heesterman reported that adding epicsShareExtern inside the C file 
solves the build problem so that is what I did. The code in 2.1.16 slightly 
differs from his proposed fix because gcc gave a warning about initializing a 
variable that was declared extern, so the code is now:

  epicsShareExtern double seq_sync_timeout;
  double seq_sync_timeout = 10.0;

> I suspect that just marking the definition as epicsShareExtern in the
> seq_if.c file may cause problems later.

I hope not ;-) At least, it seems that currently __declspec(dllimport) is not 
really needed. If it turns out later that there are cases where it is needed, 
I will add the necessary annotation in the code where the variable is used 
(inside the tests).

Let me repeat: if you intend your programs to work with future releases of the 
sequencer, you should *not* use this variable. I may remove it without further 
notice. A proper fix for the issue of configuring the timeout for the SYNC 
variants of pvPut and pvGet will appear in version 2.2 of the sequencer.

Cheers
Ben

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System