C++ and JVM Heap

Question

Hi, just a short question. If I call a native method from Java which read a large file into memory, it consume the JVM heap or its own memory?
Thanks.

Answer 1

Can't say for sure where the problem is (though DO hope that it's some error in the code - otherwise i'd be in trouble - starting to write a code based on storing large data structures in native part), but two suggestions:
1) error is 'file i/o' specific, meaning that probably you are running out of some IO resources (which means that DLL is probably written incorrectly or some specific memory area of JVM is to be increases - see HotSpot tuning). I recall that you are getting the error during memory allocation error, but still...
2) .... probably smth else :) (just forgot what was the second one...)
Try this workaround: start up JVM from native code and read the file into JVM from that layer
eg, event based model:
// native code
main() {
*p = CreateJVM();
while (true) {
   if (p->doReadFile()) {
     file* f = readFile();
     p->setFileBytes(f->toByteArray());
   sleep();
// java code
void readFile() {
  setDoReadFile(true);
  while (!isDataReady())   wait(1000);
  byte[] arr = getFileBytes();
}This way you'd be sending data TO JVM, not reading it FROM JVM. I guess there might be other way to implement this kind of solution (still JVM driven, but with reading data not into memory allocated from JVM, but into the process the JVM itself was started from - by passing a pointer to this main process into Java and then into native method or smth like that, but don't know for sure how to do this).
I'll run appox. the same test (without reading data from the file but generating it from Java code) under Linux and let you know the results.