Re: Can't allocate large char array in JNI

Gordon Beaton <>
22 Apr 2008 05:46:23 GMT
On Mon, 21 Apr 2008 08:07:08 -0700 (PDT), CD1 wrote:

The jchar *value comes from the object allocated by the library
OpenCV, ant its size is the imageSize field of the IplImage struct.

What is the real declared type of the cv_image->imageData, i.e. before
the explicit typecast?

What are "sizeof(jchar)" and "sizeof(cv_image->imageData[0])"?

Here's something you can test, add this to the start of set_char_array()
before calling any of the jni functions:

  volatile jchar tmp;
  int i;

  for (i=0; i<length; i++) {
    tmp = value[i];

Does this code pass ok?

Try a small example without using your image library. With the
following code I can successfully allocate char arrays of 30MB using
the default java heap size. Beyond that, ExceptionDescribe() correctly
identifies the error as "Out of memory: Java heap space":

  // public static native char[] getCharArray(int n);

  Java_Chars_getCharArray(JNIEnv *env, jclass unused, jint n)
    jcharArray jca;
    jchar *jc;
    int i;

    jca = (*env)->NewCharArray(env, n);

    if ((*env)->ExceptionOccurred(env)) {

    if ((jc = malloc(n * sizeof(jchar)))) {
      // some nonsense initial values
      for (i=0; i<n; i++) {
        jc[i] = i % 255;

      (*env)->SetCharArrayRegion(env, jca, 0, n, jc);

      if ((*env)->ExceptionOccurred(env)) {


    return jca;



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