JNI Multithread Question in Linux

Dear friends,

 

I have successfully integrated native (C++) codes which employ threading
operation with a simple java program. The objective of the program is to
spawn thread (using POSIX pthread_create) that prints 10 "Hello World"
in approx. 10 seconds.     

 

My Software environment

JBuilder9 (jdk1.4) in Linux 7.2

 

I have created a shared library

A shared library libhelloworld.so (g++ using native CJNI_Layer.cpp &
CNative.cpp) is created.

 

Running the application

java CJNI_Layer

 

Java Program Output

Native thread prints "Hello World" 10 times (in approx. 10 seconds)
before returning to Java program (CJNI_Layer.java)

 

Seems that I have achieved what I wanted. However, a closer look at the
java program depicts that the thread should terminate and exit way
before the Native Method ThreadFunction() completes its execution of
printing 10 "Hello World". This is because the java program (main
process) should have exited before the native method completes
execution.

 

It appears to me that the native thread has seized the entire flow of
control from java program and it is not running independently. Why is
that so? How can I make the native thread independent and not seize the
flow of control from the java program? I would really appreciate if you
can my answer my questions. Thank you very much.

 

JJ

 

--- CJNI_Layer.java ---

class CJNI_Layer

{

            static

{

                        try

                        {

                                    System.loadlibrary("helloworld");

                        }

                        catch (UnsatisfiedLinkError ule)

                        {

                                    System.out.println(ule);

                        }

            }

 

            private native int SpawnThread();

 

            public static void main(String args [])

            {

                        CJNI_Layer c = new CJNI_Layer();

 

                        c.SpawnThread();

            }

} 

 

--- CJNI_Layer.cpp --- 

#include CJNI_Layer.h    // generated by javah

#include "CNative.h"       // defines structure of Class CNative

 

JNIEXPORT jint JNICALL Java_CJNI_Layer_ SpawnThread(JNIEnv *, jobject)

{

            CNative native_class;                 // an array of CNative

            native_class.SpawnThread();       

            return 0;

}

 

--- CNative.cpp --- native implementation in C++

#include <unistd.h>

#include <stdio.h>

#include "CNative.h"

 

void *thread_func(void *p)            // this function is declared as a
friend to CNative in CNative.h

{

            CNative *pCNative = reinterpret_cast<CNative *>(p);

            If(pCNative)

                        pCNative->ThreadFunction();

            return 0;

}

 

void CNative::ThreadFunction()

{

            for (int i = 0; i < 10; i++){

                        printf("\nHello World");

                        sleep(1);

            }

            return;

}

 

int CNative::SpawnThread()

{

            int res = pthread_create(&thread, NULL, thread_func, this);
// protected class member pthread_t thread

            return res;

}