/*

 * Copyright (c) 2004, 2011, 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:

 *

 *   - Redistributions of source code must retain the above copyright

 *     notice, this list of conditions and the following disclaimer.

 *

 *   - Redistributions 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 nor the names of its

 *     contributors may be used to endorse or promote products derived

 *     from this software without specific prior written permission.

 *

 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS

 * IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,

 * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR

 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT OWNER OR

 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,

 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,

 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR

 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF

 * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING

 * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS

 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

 */

/*

 * This source code is provided to illustrate the usage of a given feature

 * or technique and has been deliberately simplified. Additional steps

 * required for a production-quality application, such as security checks,

 * input validation and proper error handling, might not be present in

 * this sample code.

 */

/* 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)

{

}