/*
 * %W% %E%
 * 
 * Copyright (c) 2006, Oracle and/or its affiliates. All rights reserved.
 * 
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 * 
 * -Redistribution of source code must retain the above copyright notice, this
 *  list of conditions and the following disclaimer.
 * 
 * -Redistribution in binary form must reproduce the above copyright notice, 
 *  this list of conditions and the following disclaimer in the documentation
 *  and/or other materials provided with the distribution.
 * 
 * Neither the name of Oracle or the names of contributors may 
 * be used to endorse or promote products derived from this software without 
 * specific prior written permission.
 * 
 * This software is provided "AS IS," without a warranty of any kind. ALL 
 * EXPRESS OR IMPLIED CONDITIONS, REPRESENTATIONS AND WARRANTIES, INCLUDING
 * ANY IMPLIED WARRANTY OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE
 * OR NON-INFRINGEMENT, ARE HEREBY EXCLUDED. SUN MICROSYSTEMS, INC. ("SUN")
 * AND ITS LICENSORS SHALL NOT BE LIABLE FOR ANY DAMAGES SUFFERED BY LICENSEE
 * AS A RESULT OF USING, MODIFYING OR DISTRIBUTING THIS SOFTWARE OR ITS
 * DERIVATIVES. IN NO EVENT WILL SUN OR ITS LICENSORS BE LIABLE FOR ANY LOST 
 * REVENUE, PROFIT OR DATA, OR FOR DIRECT, INDIRECT, SPECIAL, CONSEQUENTIAL, 
 * INCIDENTAL OR PUNITIVE DAMAGES, HOWEVER CAUSED AND REGARDLESS OF THE THEORY 
 * OF LIABILITY, ARISING OUT OF THE USE OF OR INABILITY TO USE THIS SOFTWARE, 
 * EVEN IF SUN HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES.
 * 
 * You acknowledge that this software is not designed, licensed or intended
 * for use in the design, construction, operation or maintenance of any
 * nuclear facility.
 */

/* Example of using JVMTI_EVENT_GARBAGE_COLLECTION_START and
 *                  JVMTI_EVENT_GARBAGE_COLLECTION_FINISH events.
 */

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#include "jni.h"
#include "jvmti.h"

/* For stdout_message(), fatal_error(), and check_jvmti_error() */
#include "agent_util.h"

/* Global static data */
static jvmtiEnv     *jvmti;
static int           gc_count;
static jrawMonitorID lock;

/* Worker thread that waits for garbage collections */
static void JNICALL
worker(jvmtiEnv* jvmti, JNIEnv* jni, void *p) 
{
    jvmtiError err;
    
    stdout_message("GC worker started...\n");

    for (;;) {
        err = (*jvmti)->RawMonitorEnter(jvmti, lock);
        check_jvmti_error(jvmti, err, "raw monitor enter");
	while (gc_count == 0) {
	    err = (*jvmti)->RawMonitorWait(jvmti, lock, 0);
	    if (err != JVMTI_ERROR_NONE) {
		err = (*jvmti)->RawMonitorExit(jvmti, lock);
                check_jvmti_error(jvmti, err, "raw monitor wait");
		return;
	    }
	}
	gc_count = 0;
        
	err = (*jvmti)->RawMonitorExit(jvmti, lock);
	check_jvmti_error(jvmti, err, "raw monitor exit");

	/* Perform arbitrary JVMTI/JNI work here to do post-GC cleanup */
	stdout_message("post-GarbageCollectionFinish actions...\n");
    }
}

/* Creates a new jthread */
static jthread 
alloc_thread(JNIEnv *env) 
{
    jclass    thrClass;
    jmethodID cid;
    jthread   res;

    thrClass = (*env)->FindClass(env, "java/lang/Thread");
    if ( thrClass == NULL ) {
	fatal_error("Cannot find Thread class\n");
    }
    cid      = (*env)->GetMethodID(env, thrClass, "<init>", "()V");
    if ( cid == NULL ) {
	fatal_error("Cannot find Thread constructor method\n");
    }
    res      = (*env)->NewObject(env, thrClass, cid);
    if ( res == NULL ) {
	fatal_error("Cannot create new Thread object\n");
    }
    return res;
}

/* Callback for JVMTI_EVENT_VM_INIT */
static void JNICALL 
vm_init(jvmtiEnv *jvmti, JNIEnv *env, jthread thread)
{
    jvmtiError err;
    
    stdout_message("VMInit...\n");

    err = (*jvmti)->RunAgentThread(jvmti, alloc_thread(env), &worker, NULL,
	JVMTI_THREAD_MAX_PRIORITY);
    check_jvmti_error(jvmti, err, "running agent thread");
}

/* Callback for JVMTI_EVENT_GARBAGE_COLLECTION_START */
static void JNICALL 
gc_start(jvmtiEnv* jvmti_env) 
{
    stdout_message("GarbageCollectionStart...\n");
}

/* Callback for JVMTI_EVENT_GARBAGE_COLLECTION_FINISH */
static void JNICALL 
gc_finish(jvmtiEnv* jvmti_env) 
{
    jvmtiError err;
    
    stdout_message("GarbageCollectionFinish...\n");

    err = (*jvmti)->RawMonitorEnter(jvmti, lock);
    check_jvmti_error(jvmti, err, "raw monitor enter");
    gc_count++;
    err = (*jvmti)->RawMonitorNotify(jvmti, lock);
    check_jvmti_error(jvmti, err, "raw monitor notify");
    err = (*jvmti)->RawMonitorExit(jvmti, lock);
    check_jvmti_error(jvmti, err, "raw monitor exit");
}

/* Agent_OnLoad() is called first, we prepare for a VM_INIT event here. */
JNIEXPORT jint JNICALL
Agent_OnLoad(JavaVM *vm, char *options, void *reserved)
{
    jint                rc;
    jvmtiError          err;
    jvmtiCapabilities   capabilities;
    jvmtiEventCallbacks callbacks;
    
    /* Get JVMTI environment */
    rc = (*vm)->GetEnv(vm, (void **)&jvmti, JVMTI_VERSION);
    if (rc != JNI_OK) {
	fatal_error("ERROR: Unable to create jvmtiEnv, rc=%d\n", rc);
	return -1;
    }

    /* Get/Add JVMTI capabilities */ 
    (void)memset(&capabilities, 0, sizeof(capabilities));
    capabilities.can_generate_garbage_collection_events = 1;
    err = (*jvmti)->AddCapabilities(jvmti, &capabilities);
    check_jvmti_error(jvmti, err, "add capabilities");

    /* Set callbacks and enable event notifications */
    memset(&callbacks, 0, sizeof(callbacks));
    callbacks.VMInit                  = &vm_init;
    callbacks.GarbageCollectionStart  = &gc_start;
    callbacks.GarbageCollectionFinish = &gc_finish;
    err = (*jvmti)->SetEventCallbacks(jvmti, &callbacks, sizeof(callbacks));
    check_jvmti_error(jvmti, err, "set event callbacks");
    err = (*jvmti)->SetEventNotificationMode(jvmti, JVMTI_ENABLE, 
			JVMTI_EVENT_VM_INIT, NULL);
    check_jvmti_error(jvmti, err, "set event notification");
    err = (*jvmti)->SetEventNotificationMode(jvmti, JVMTI_ENABLE, 
			JVMTI_EVENT_GARBAGE_COLLECTION_START, NULL);
    check_jvmti_error(jvmti, err, "set event notification");
    err = (*jvmti)->SetEventNotificationMode(jvmti, JVMTI_ENABLE, 
			JVMTI_EVENT_GARBAGE_COLLECTION_FINISH, NULL);
    check_jvmti_error(jvmti, err, "set event notification");

    /* Create the necessary raw monitor */
    err = (*jvmti)->CreateRawMonitor(jvmti, "lock", &lock);
    check_jvmti_error(jvmti, err, "create raw monitor");
    return 0;
}

/* Agent_OnUnload() is called last */
JNIEXPORT void JNICALL
Agent_OnUnload(JavaVM *vm)
{
}

