test/hotspot/jtreg/vmTestbase/gc/gctests/nativeGC02/libnativeGC02.c

/*
 * Copyright (c) 2005, 2018, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */
#include <jni.h>
#include <stdio.h>

/* A C function that takes a reference to java Object( a circular Linked list)
    and utilizes this reference to do a java method callback to determine the
    number of elements in the linked list */
JNIEXPORT jint JNICALL
Java_gc_gctests_nativeGC02_nativeGC02_nativeMethod02
(JNIEnv *env, jobject obj, jobject linked_list) {
        jclass cls, clss;
        jmethodID mid, mid2;
        jfieldID fid;
        jobject llist;
        int elementCount;

        /* Store a reference to the linked list in the C stack */

        clss = (*env)->GetObjectClass(env, obj);
        fid = (*env)->GetFieldID(env, clss, "cl", "Lnsk/share/gc/CircularLinkedList;");
        if (fid == 0) {
                printf("could not locate field - cl\n");
                return -1;
        }

        llist = (*env)->GetObjectField(env, obj, fid);

        /* force a GC by invoking a callback where System.gc() is called
        */

        cls  = (*env)->GetObjectClass(env, obj);
        mid = (*env)->GetMethodID(env, cls, "callbackGC", "()V");
        if (mid  == 0){
                printf("couldnt locate method callbackGC()\n");
                return -1;
        }
        (*env)->CallVoidMethod(env,obj,mid);

        /* Now that a GC has been done, invoke the callback
           that counts the number of elements in the
           circular linked list
           */

        clss = (*env)->GetObjectClass(env, linked_list);
        mid2 = (*env)->GetMethodID(env, clss, "getLength", "(Lnsk/share/gc/CircularLinkedList;)I" );
        if (mid2  == 0 ){
                printf("couldnt locate method getLength(CircularLinkedList)\n");
                return -1;
        }
        elementCount  = (*env)->CallIntMethod(env, linked_list, mid2, llist);
        return elementCount;
}