Java HotSpot Virtual Machine

Hello,

I have an optimized JPEG decoder written in C++, I have a JNI bridge to that codebase with this method:

Java-side:

public static native byte[] readJPEG(String name);

C++ side:

JNIEXPORT const jbyteArray JNICALL Java_IPPJPEGDecoder_readJPEG(JNIEnv *, jclass, jstring);

I have this call in Java layer:

long start = System.currentTimeMillis();

byte[] data = IPPJPEGDecoder.readJPEG("C:\\D-102_red_ink_1.JPG");

long end = System.currentTimeMillis();

System.out.println("total time = " + (end - start));

This is my method in C++ (rough/ugly code, don't judge me :) )

JNIEXPORT const jbyteArray JNICALL Java_IPPJPEGDecoder_readJPEG (JNIEnv * env, jclass jobj, jstring jpeg_filename)
{
    //cout << "INVOKED IPPJPEGDecoder.readJPEG() SUCCESSFULL" << endl;
    //cout << "Started"<<endl;
    CIppImage m_image;
    CIppImage grayscale_image;
    CIppImage monochrome_image;
    CTimer timer;
    timer.Start();
    CStdFileInput in;
    const IppLibraryVersion* libver = ippGetLibVersion();
    cout << "LibraryVersion = (" << libver->Name <<": " << libver->Version << ")"<<endl;
    UIC::BaseStream::TStatus status;
    jboolean iscopy;
    const char * filename = env->GetStringUTFChars(jpeg_filename,&iscopy);
    status = in.Open(filename);
    GetImageFromJPEGJNI(in, m_image, timer);
    cout<<"m_image: (Precision: " << m_image.Precision() << ", NumChannels: " <<m_image.NChannels()<<", Width: " << m_image.Width() << ", Height: " << m_image.Height()<< ", Color: " << m_image.Color() <<", step: " << m_image.Step()<<endl;
    timer.Start();
    cout << "data array size of image : " <<(m_image.Step()*m_image.Height())<<endl;
    jbyteArray jb = env->NewByteArray(m_image.Step()*m_image.Height());
    env->SetByteArrayRegion(jb,0, m_image.Step()*m_image.Height(),(const jbyte*)m_image.DataPtr());
    timer.Stop();
    double mytime = timer.GetTime();
    cout << "JNI occurred in " << mytime << " ms"<<endl;
    return jb;
    //return NULL;
}

When I call this code, the C++ codeblock reports as running in 92.7793 ms

My java code reports back: 572 ms

is the Call to the JNI method THAT INSANELY slow !?!?! I MUST be doing something wrong... this is in Windows XP and I'm linking against my own dll that I compiled in Microsoft Visual C++ 2008.

The jbyteArray that I'm passing back has a length of 33583500
... maybe it's the conversion from jbyteArray to Java's byte[] that is causing all the overhead.... are there any ways around that?

Thanks!!

Alessandro Ferrucci