asked on

JNI from Servlet / free memory inside C routine

I use JNI to call a native C routine from a Servlet.
My routine is shaped like this :

JNIblahblah (JNIEnv *env, jobject obj)
{
...
char *buffer_out;
...
buffer_out = (char *)calloc(255,1);
...
return(*env)->NewStringUTF(env, buffer_out);
}

My question is : as this routine will be called very often (concurrent acces), is it MANDATORY to free 'buffer_out'
before leaving the routine ? (please explain)

Thanks for any info

mbormann

from TiJ

It would seem that finalize( ) is in place because of the possibility that you’ll do something C-like by allocating memory using a mechanism other than the normal one in Java. This can happen primarily through native methods , which are a way to call non-Java code from Java. (Native methods are discussed in Appendix A.) C and C++ are the only languages currently supported by native methods, but since they can call subprograms in other languages, you can effectively call anything. Inside the non-Java code, C’s malloc( ) family of functions might be called to allocate storage, and unless you call free( ) that storage will not be released, causing a memory leak. Of course, free( ) is a C and C++ function, so you’d need call it in a native method inside your finalize( ).

It seems that since u r doing this many times,call a Native Method which is passed this returned pointer and whose only job is to free(),i.e u shift finalize() code to this method called say

void freeResources();

Eric98

ASKER

Actually my servlet is executed only once, and so would be the finalize.
But each time the servlet is requested, a new JNI call will be instantiated : it is the JNI call that happens very often.
So the meaning of my question is : do I have to free the ressources allocated by the C JNI call before leaving
the C, or will this be done on an automatic basis, in the same way as the ressources of a regular C program, once completed, are freed by the Operating system.

mbormann

>>>>>
Do I have to free theressources allocated by the C JNI call before leaving the C, or will this be done on an automatic basis,

you have to free it by urself ,u can use System.runFinalizersOnExit(true); for true blue Applications

Oops I forgot b4 but the same functionality that finalize() provides in applications s provided in servlets in destroy() so have it there but mostly the servlet class file si goingt o be in Memory so better call that free routine by urself.

Do it else u have a 'leak'

Eric98

ASKER

Thanks for your help.
Please make a response so I can give you the points.
And please tell me what true blue application means?

Eric98

ASKER

Thanks for your help.
Please make a response so I can give you the points.
And please tell me what true blue application means?

ASKER CERTIFIED SOLUTION

mbormann

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