Name: krC82822 Date: 08/07/2001


7 Aug 2001, kevin.ryan@eng -- reproducible with 1.3.1 and 1.4 beta (build 65)
on Solaris 2.8 (please also see Comments section)
----------------
java version "1.3.1"
Java(TM) 2 Runtime Environment, Standard Edition (build 1.3.1-b24)
Java HotSpot(TM) Client VM (build 1.3.1-b24, mixed mode)

When invoking methods through the invocation API, trying to obtain the context
ClassLoader for a Thread will return null
unless the Thread is the main Thread which was used to create the JVM.

In a simple example, I have Thread 1 which creates a JVM and invokes a method on
a class. I then launch a second Thread
which invokes the same method on the class. In Thread 1 is the context
classloader ok (it is the application classloader).
In Thread 2 though, the Thread.getContextClassLoader() returns null.


********* Java Code *********
public final class JVMInvoker
{
      public static void invoke() {
              Thread me = Thread.currentThread();
              
              System.out.println(
                      "JAVA: Calling Thread : " + me
              );
              System.out.println(
                      "JAVA: ContextClassLoader: " + me.getContextClassLoader()
              );
      }
}


********* Invocation Code *********
#include <pthread.h>

#include <jni.h>
#include <malloc.h>
#include <stdlib.h>


//------------------------------------------------------
// Globals

static JavaVM* m_JVM;
static jmethodID m_JavaInvokerMID;
static jclass m_JavaInvokerClazz;



//------------------------------------------------------
// Function Decls

extern "C" {
void createJavaVM();
void invokeMethod();
void* launchThread(void*);
}


//------------------------------------------------------
// Main

static JavaVM* jvm = NULL;

int main(int, char**)
{
fprintf(stdout, "\n");

// creates the VM and calls invokeMethod
createJavaVM();

fprintf(stdout, "\n");

pthread_t tid;
pthread_create(&tid, NULL, launchThread, NULL);

fprintf(stdout, "\n");
}


//------------------------------------------------------
// createJavaVM

void createJavaVM()
{
JNIEnv* env = NULL;

JavaVMInitArgs vm_args;
JavaVMOption* options = (JavaVMOption*)malloc(sizeof(JavaVMOption));

options[0].optionString = (char*)"-Djava.class.path=.";
options[0].extraInfo = (void*)0;

vm_args.version = JNI_VERSION_1_2;
vm_args.options = options;
vm_args.nOptions = 1;
vm_args.ignoreUnrecognized = JNI_FALSE;

jint result = JNI_CreateJavaVM(&m_JVM, (void**)&env, &vm_args);
if ( result != JNI_OK ) {
fprintf(stderr, "\nCould not create JAVA VM\n");
exit(1);
}

const char* name = "JVMInvoker";
jclass clazz = env->FindClass(name);
if ( clazz == NULL ) {
fprintf(stderr, "\nCould not load 'JVMInvoker'\n");
exit(1);
}

m_JavaInvokerMID = env->GetStaticMethodID(clazz, "invoke", "()V");
if ( m_JavaInvokerMID == 0 ) {
fprintf(stderr, "\nCould not find method invoke()\n");
exit(1);
}

m_JavaInvokerClazz = (jclass)env->NewGlobalRef(clazz);


// now invoke method in same thread
fprintf(
stdout, "CPP : Thread (%d): Invoking JVMInvoker .... OK\n",
pthread_self()
);
invokeMethod();
}

//------------------------------------------------------
// invokeMethod

void invokeMethod()
{
JNIEnv* env = NULL;

jint result = m_JVM->AttachCurrentThread((void**)&env, 0);
if ( result != JNI_OK ) {
fprintf(
stderr,
"\nCould not attach current thread to JVM: Thread = %d",
pthread_self()
);
exit(1);
}

fprintf(stdout, "CPP : Calling Thread = %d\n", pthread_self());
env->CallStaticVoidMethod(
m_JavaInvokerClazz,
m_JavaInvokerMID
);
}

//------------------------------------------------------
// launchThread

void* launchThread(void*)
{
fprintf(
stdout, "CPP : Thread (%d): Invoking JVMInvoker .... NOK\n",
pthread_self()
);
invokeMethod();

return (void*)0;
}


********* Makefile *********
#-----------------------------------------------------------------
# Vars

CC = /opt/workshop6u1/bin/CC

JAVA_HOME=/opt/java/jdk/1.3.1
#JAVA_HOME=/opt/java/jdk/1.2.2_05a

FLAGS = -DDEBUG -g +w2 -KPIC -mt
INCLS = -I. -I$(JAVA_HOME)/include/solaris -I$(JAVA_HOME)/include
LIBS = -L$(JAVA_HOME)/jre/lib/sparc -ljvm

CPP_SOURCES = JVMInvoker.cpp

JAVA_SOURCES = JVMInvoker.java

EXENAME = jvminoker


#-----------------------------------------------------------------
# Rules

all: java_compile exe

java_compile:
$(JAVA_HOME)/bin/javac -g -d . $(JAVA_SOURCES)


exe:
$(CC) -o $(EXENAME) $(FLAGS) $(INCLS) $(CPP_SOURCES) $(LIBS)

run:
CLASSPATH=. LD_LIBRARY_PATH=$(JAVA_HOME)/jre/lib/sparc $(EXENAME)


clean:
\rm -fr *.o *~ $(EXENAME) *.class
(Review ID: 128509)
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