Hi, Andrew. You're right that using gcj or g++ to link doesn't matter. The difference with what I was doing before was the compiler/linker options. One more question. Is there any advantage to converting a .jar library to a .so library and using it as opposed to simply using the original .jar file with the Java invocation API and the JNI to call back to C++ from Java? I thought I would get a performance increase with using the .so library but perhaps there are no substantive differences between the two approaches. Thanks again for all your help! -Joe On Tue, 2007-12-04 at 16:42 +0000, Andrew Haley wrote: > Joe Hoffert writes: > > Hi, Andrew. > > > > On Tue, 2007-12-04 at 15:59 +0000, Andrew Haley wrote: > > > Joe Hoffert writes: > > > > Hi, Andrew. > > > > > > > > On Tue, 2007-12-04 at 15:16 +0000, Andrew Haley wrote: > > > > > > > > OK. I've attached a zip file with everything that should be needed. The > > > > gcj-commands file simply contains the gcj and gcjh commands I used to > > > > generate the .so library and the .h header files. > > > > > > Works for me: > > > > > > zorro:tmp $ gcjh -classpath ./ricochet.jar multishot.examples.RicochetApp > > > zorro:tmp $ gcj -shared -fPIC -Wl,-Bsymbolic ./ricochet.jar -o libricochet.so > > > zorro:tmp $ gcj RicochetAppMain.cpp -L. -lricochet -fPIC -lstdc++ > > > cc1plus: warning: command line option "-fbootclasspath=./:/usr/share/java/libgcj-4.1.2.jar" is valid for Java but not for C++ > > > > Ah! This is the missing piece for me. I was linking with g++. I was > > assuming since I had a .so library and .h headers I could treat the > > transformed .jar file like a C++ library. It never crossed my mind to > > compile the C++ file with gcj and link everything with gcj. > > > > I assume I will need to use gcj rather than g++ for all my C++ files. Is > > this correct? > > I don't think it matters. I could have done this instead: > > zorro:tmp $ g++ RicochetAppMain.cpp -L. -lricochet -fPIC -lgcj > zorro:tmp $ LD_LIBRARY_PATH=. ./a.out > > > > Usage: RicochetApp GMS_id FDS_id startPortNumber [propertyString] > > > > > > You really need to call JvCreateJavaVM() first. > > > > In some other code I have I call JNI_CreateJavaVM. Is this > > different from JvCreateJavaVM and, if so, do you know how it > > differs? The prototype for JvCreateJavaVM doesn't exist in the > > jni.h file that I'm using. > > No, but it is included. You must call JvCreateJavaVM() as the very > first call into libgcj. This is *really* important. > > > Adding this call raises some questions for me. Does this call add > > overhead (and/or footprint)? I was (seemingly naively) assuming > > that once the .jar file was converted to a .so file I was done with > > needing any Java support. This doesn't seem to be the case. Why is > > the JVM still needed? > > There's a ton of stuff: threads, garbage collection, and of course the > entire Java runtime library. > > > Are there any other calls I should add? > > I can't think of any. > > Andrew. >
