[Cbc] Invoking the Cbc solver from a Java application via JNI.

[acw at ascent.com]

We found an amelioration for the problem that I described earlier, where 
our application was segfaulting upon calling CbcMain1.  I'm going to 
describe it because at least two people on this list mentioned similar 
problems.

There are two definitions of CbcMain1, with different calling signatures. 
One is a three-argument function, while the other takes four arguments. 
Our application calls the three-argument version, which in turn calls the 
four-argument version.  It is the inner call to the four-argument CbcMain1 
that segfaults.

Our current theory is that JNI is failing to keep straight the multiple 
CbcMain1's in the symbol table.  The problem goes away if you rename the 
four-argument version, and have the three-argument version call the 
renamed function rather than the original.

The COIN/OR project should not be responsible for working around JNI's 
bugs; but that having been said, it would help if the two functions called 
CbcMain1 were given different names.



From:
acw at ascent.com
To:
cbc at list.coin-or.org
Cc:
dev at ascent.com
Date:
08/13/2009 05:08 PM
Subject:
[Cbc] Invoking the Cbc solver from a Java application via JNI.




We have a Cbc application that is invoked from Java using the Java Native 
Interface (JNI). 

We're working under Linux. 

We build a shared-object (.so) library which provides an entry-point very 
much like driver4's "main".  This entry works fine when called straight 
from C++ code.  But when called via JNI it fails in a weird way.  It 
throws a segmentation fault immediately after entering the function 
CbcMain1.  I moved debugging statements around the entry to CbcMain1, and 
I can't resolve the place the fault is signalled: it looks like it happens 
as part of the calling sequence to CbcMain1. 

A call to CbcMain0, a few lines upstream, completes successfully. 

Has anyone else succeeded in using Cbc from Java/JNI, and do you have any 
advice to offer?  I am suspecting that some of the compilation flags in 
the Cbc build process violate JNI's expectations about library structure, 
but this vague suspicion doesn't explain why CbcMain0 works and CbcMain1 
fails._______________________________________________
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