[Plplot-cvs] CVS update notice (plplot/cf)

[Geoffrey F. <fu...@us...>]

Update of /cvsroot/plplot/plplot/cf
In directory usw-pr-cvs1:/tmp/cvs-serv5657/cf

Modified Files:
	dyndrv.in 
Log Message:
Fix very tricky error in building of the dynloadable drivers.

C programs like x01c were working fine with dynamic drivers, but only
accidentally.  Specifically, references by the drivers to functions
provided by libplplot, were being resolved in some cases as a result
of the peculiarities of how the final executable was being built.

However, in the case of the java binding, we don't control the way in
which Java's System.loadLibrary( "plplot" ); manages the interraction
with dlopen(), so we have to prime the pump.  To make it all work, we
have to actually link the drivers against libplplot.so, so that when
the drivers are dynloaded into libplplot during the Java static init
section in PLStream.java, they will actually resolve symbols against
the (already loaded) libplplot.so.  

It all comes down to understanding dlopen() and friends.  Evidently
when the JVM does the external (native) load, it won't use
RTLD_GLOBAL.  I guess that makes some kind of sense from a security
standpoint, although it complicates the situation for dynloadable
libraries which want to dynload additional components.  

Anyway, it works now.  The dynamic drivers can be loaded into
executable programs compiled in the usual way (shown by the PLplot
makefile), or into libplplot.so when libplplot.so is itself dynloaded
into some other process, such as occurs in the case of the JVM loading
the PLplot JNI binding dynamically.

Cool.