1 /*
   2  * Copyright (c) 2005, 2018, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.
   8  *
   9  * This code is distributed in the hope that it will be useful, but WITHOUT
  10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  11  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  12  * version 2 for more details (a copy is included in the LICENSE file that
  13  * accompanied this code).
  14  *
  15  * You should have received a copy of the GNU General Public License version
  16  * 2 along with this work; if not, write to the Free Software Foundation,
  17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  18  *
  19  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  20  * or visit www.oracle.com if you need additional information or have any
  21  * questions.
  22  */
  23 #include <jni.h>
  24 #include <stdio.h>
  25 
  26 extern "C" {
  27 
  28 /* A C function that takes a reference to java Object(a circular Linked list)
  29     and utilizes this reference to do a java method callback to determine the
  30     number of elements in the linked list */
  31 JNIEXPORT jint JNICALL
  32 Java_gc_gctests_nativeGC02_nativeGC02_nativeMethod02
  33 (JNIEnv *env, jobject obj, jobject linked_list) {
  34         jclass cls, clss;
  35         jmethodID mid, mid2;
  36         jfieldID fid;
  37         jobject llist;
  38         int elementCount;
  39 
  40         /* Store a reference to the linked list in the C stack */
  41 
  42         clss = env->GetObjectClass(obj);
  43         fid = env->GetFieldID(clss, "cl", "Lnsk/share/gc/CircularLinkedList;");
  44         if (fid == 0) {
  45                 printf("could not locate field - cl\n");
  46                 return -1;
  47         }
  48 
  49         llist = env->GetObjectField(obj, fid);
  50 
  51         /* force a GC by invoking a callback where System.gc() is called
  52         */
  53 
  54         cls = env->GetObjectClass(obj);
  55         mid = env->GetMethodID(cls, "callbackGC", "()V");
  56         if (mid == 0) {
  57                 printf("couldnt locate method callbackGC()\n");
  58                 return -1;
  59         }
  60         env->CallVoidMethod(obj,mid);
  61 
  62         /* Now that a GC has been done, invoke the callback
  63            that counts the number of elements in the
  64            circular linked list
  65            */
  66 
  67         clss = env->GetObjectClass(linked_list);
  68         mid2 = env->GetMethodID(clss, "getLength", "(Lnsk/share/gc/CircularLinkedList;)I");
  69         if (mid2 == 0) {
  70                 printf("couldnt locate method getLength(CircularLinkedList)\n");
  71                 return -1;
  72         }
  73         elementCount = env->CallIntMethod(linked_list, mid2, llist);
  74         return elementCount;
  75 }
  76 
  77 }