Help calling JNI function from a java thread

Question

I am using the following code to call a JNI fuction from a java thread:
public class CMSMessageHandler extends MessageHandler{
static{
System.loadLibrary("jastb");
public native int cmsReadIt(ByteBuffer buff);
private ByteBuffer dirbuf = null;
/** Creates a new instance of CMSMessageHandler */
public CMSMessageHandler() {
// allocate to max size datagram
dirbuf = ByteBuffer.allocateDirect(65536);
public void readMessages(){
/*Thread worker = new Thread(){
public void run(){*/
int count;
while (true){
try{
count = cmsReadIt(dirbuf);
} catch (Exception e){
e.printStackTrace();
worker.start();*/
public static void main(String[] args) {
CMSMessageHandler handler = new CMSMessageHandler();
handler.readMessages();
When I run this main method with the thread commented out, it works great. When I run the main method with the thread, it works great for a while, and then funny things start happening with the native library I am using. My native library uses shared memory, signals, and semaphores. It feels a bit like my java program is stomping on the resources that my native library is using, when a run the java program with a thread.
Is there something I don't know about calling native code from a thread? Should I be doing something explicitly to protect my native library's shared memory, signals, or semaphores?
Thanks,
Lisa.

Answer 1

Does the library do any initialization when loaded? Does it make a dangerous assumption that the thead calling cmdReadIt will always be the same thread that initially loaded it? Try loading the library in the worker thread instead of in the main thread via the static initializer.Yes. There is a call to another native method cmsOpenIt that does CMS initialization. I put cmsOpenIt as well as the System.loadLibrary("jastb") in the worker thread and I'm still experiencing the same problems.
Incidently, the mere presence of another Thread in this program does not seem to cause problems. It's only when I run calls to cmsReadIt in a thread that I get into trouble.
For example, this works fine:
public class CMSMessageHandler extends MessageHandler{
    public native int cmsReadIt(ByteBuffer buff);
    public ByteBuffer dirbuf = null;
    static {
        System.loadLibrary("jastb");
    public CMSMessageHandler() {
        // allocate to max size datagram
        dirbuf = ByteBuffer.allocateDirect(65536);
    public void readMessages(){
        try{
            int count = 0;
            while (true){
                count = cmsReadIt(dirbuf);
        } catch (Exception e){
    public static void main(String[] args) {
        CMSMessageHandler handler = new CMSMessageHandler();
        Thread worker = new Thread(){
            public void run(){
                while (true){
                    try{
                        Thread.currentThread().sleep(1000);
                        System.out.println("sleep thread.");
                    } catch (Exception e){
                        e.printStackTrace();
        worker.start();
        handler.readMessages();  
    }Are there JVM flags that I should experiment with that might help mitigate/diagnose this problem?