JDK system dependency: link against libjvm

Describe the bug jni.h does not only contain structures to run c(++) code from java, but also java from c(++). For this to work the resulting binary has to be linked against libjvm.so located in $JAVA_HOME/lib/server/. Otherwise if your code tries to call these, the linker will fail:

FAILED: mjvmtest 
cc  -o mjvmtest mjvmtest.p/jvm.c.o -Wl,--as-needed -Wl,--no-undefined
/usr/lib64/gcc/x86_64-suse-linux/11/../../../../x86_64-suse-linux/bin/ld: mjvmtest.p/jvm.c.o: in function `main':
/home/admin/workspace/cli/meson/mjvmtest/_build/../jvm.c:16: undefined reference to `JNI_CreateJavaVM'
collect2: error: ld returned 1 exit status
ninja: build stopped: subcommand failed.

To Reproduce I’ve taken the JNI Invokation Example: https://docs.oracle.com/en/java/javase/11/docs/specs/jni/invocation.html, ported it to C and made it actually do something.

#include <jni.h>	/* where everything is defined */
#include <stdbool.h>

int main(int, char**) {
	JavaVM *jvm;	/* denotes a Java VM */
	JNIEnv *env;	/* pointer to native method interface */
	JavaVMInitArgs vm_args;	/* JDK/JRE 10 VM initialization arguments */
	JavaVMOption options[2];
	options[0].optionString = "-Djava.class.path=/usr/lib64/java";
	options[1].optionString = "-Xcheck:jni";
	vm_args.version = JNI_VERSION_10;
	vm_args.nOptions = 1;
	vm_args.options = options;
	vm_args.ignoreUnrecognized = false;
	/* load and initialize a Java VM, return a JNI interface
	* pointer in env */
	JNI_CreateJavaVM(&jvm, (void**)&env, &vm_args);
	/* get stdout PrintStream */
	jclass system = (*env)->FindClass(env, "java/lang/System");
	jfieldID jstdout_id = (*env)->GetStaticFieldID(env, system, "out", "Ljava/io/PrintStream;");
	jobject jstdout = (*env)->GetStaticObjectField(env, system, jstdout_id);
	/* invoke println method of PrintStream */
	jclass print_stream = (*env)->FindClass(env, "java/io/PrintStream");
	jmethodID mid = (*env)->GetMethodID(env, print_stream, "println", "(Ljava/lang/String;)V");
	jstring to_print = (*env)->NewStringUTF(env, "Hello World from C");
	(*env)->CallVoidMethod(env, jstdout, mid, to_print);
	/* We are done. */
	(*jvm)->DestroyJavaVM(jvm);
}

project('mjvmtest', 'c',
	version : '0.1',
	default_options : ['warning_level=3', 'c_std=gnu2x'])

app = executable('mjvmtest', [
		'jvm.c'
	],
	dependencies: [
		#dependency('jdk', version: ['>=11', '<12'])
		dependency('jdk', version: '>=11')
	],
	install : true
)

Expected behavior I expect it to link against libjvm.so.

Adding self.link_args = [f'{self.java_home}/lib/server/libjvm.so']to the JDKSystemDependency init method in mesonbuild/depenencies/dev.py makes it work.

What needs to be done is to extend it that it uses the correct file extension for each OS and maybe link it in a way that libjvm.so does not have to be in the library search path.

system parameters

• OS: openSUSE Tumbleweed 20211117
• Python 3.8.12
• Meson 0.59.4 & cc80187
• Ninja 1.10.2

[tristan957]

I would assume one use case for this is embedding a JVM in another application. Thanks. I will switch to modules. The default behavior would stay as “just add the include directories” since most people probably aren’t linking to the JVM libraries.

[tristan957]

Right. Information around this is pretty hard to come by to be honest. Will have a PR up in a bit