1 /*
2 * Copyright (c) 2004, 2011, Oracle and/or its affiliates. All rights reserved.
3 *
4 * Redistribution and use in source and binary forms, with or without
5 * modification, are permitted provided that the following conditions
6 * are met:
7 *
8 * - Redistributions of source code must retain the above copyright
9 * notice, this list of conditions and the following disclaimer.
10 *
11 * - Redistributions in binary form must reproduce the above copyright
12 * notice, this list of conditions and the following disclaimer in the
13 * documentation and/or other materials provided with the distribution.
14 *
15 * - Neither the name of Oracle nor the names of its
16 * contributors may be used to endorse or promote products derived
17 * from this software without specific prior written permission.
18 *
19 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
20 * IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
21 * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
22 * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
23 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
24 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
25 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
26 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
27 * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
28 * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
29 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
30 */
31
32 /*
33 * This source code is provided to illustrate the usage of a given feature
34 * or technique and has been deliberately simplified. Additional steps
35 * required for a production-quality application, such as security checks,
36 * input validation and proper error handling, might not be present in
37 * this sample code.
38 */
39
40
41 /* Example of using JVMTI_EVENT_GARBAGE_COLLECTION_START and
42 * JVMTI_EVENT_GARBAGE_COLLECTION_FINISH events.
43 */
44
45 #include <stdio.h>
46 #include <stdlib.h>
47 #include <string.h>
48
49 #include "jni.h"
50 #include "jvmti.h"
51
52 /* For stdout_message(), fatal_error(), and check_jvmti_error() */
53 #include "agent_util.h"
54
55 /* Global static data */
56 static jvmtiEnv *jvmti;
57 static int gc_count;
58 static jrawMonitorID lock;
59
60 /* Worker thread that waits for garbage collections */
61 static void JNICALL
62 worker(jvmtiEnv* jvmti, JNIEnv* jni, void *p)
63 {
64 jvmtiError err;
65
66 stdout_message("GC worker started...\n");
67
68 for (;;) {
69 err = (*jvmti)->RawMonitorEnter(jvmti, lock);
70 check_jvmti_error(jvmti, err, "raw monitor enter");
71 while (gc_count == 0) {
72 err = (*jvmti)->RawMonitorWait(jvmti, lock, 0);
73 if (err != JVMTI_ERROR_NONE) {
74 err = (*jvmti)->RawMonitorExit(jvmti, lock);
75 check_jvmti_error(jvmti, err, "raw monitor wait");
76 return;
77 }
78 }
79 gc_count = 0;
80
81 err = (*jvmti)->RawMonitorExit(jvmti, lock);
82 check_jvmti_error(jvmti, err, "raw monitor exit");
83
84 /* Perform arbitrary JVMTI/JNI work here to do post-GC cleanup */
85 stdout_message("post-GarbageCollectionFinish actions...\n");
86 }
87 }
88
89 /* Creates a new jthread */
90 static jthread
91 alloc_thread(JNIEnv *env)
92 {
93 jclass thrClass;
94 jmethodID cid;
95 jthread res;
96
97 thrClass = (*env)->FindClass(env, "java/lang/Thread");
98 if ( thrClass == NULL ) {
99 fatal_error("Cannot find Thread class\n");
100 }
101 cid = (*env)->GetMethodID(env, thrClass, "<init>", "()V");
102 if ( cid == NULL ) {
103 fatal_error("Cannot find Thread constructor method\n");
104 }
105 res = (*env)->NewObject(env, thrClass, cid);
106 if ( res == NULL ) {
107 fatal_error("Cannot create new Thread object\n");
108 }
109 return res;
110 }
111
112 /* Callback for JVMTI_EVENT_VM_INIT */
113 static void JNICALL
114 vm_init(jvmtiEnv *jvmti, JNIEnv *env, jthread thread)
115 {
116 jvmtiError err;
117
118 stdout_message("VMInit...\n");
119
120 err = (*jvmti)->RunAgentThread(jvmti, alloc_thread(env), &worker, NULL,
121 JVMTI_THREAD_MAX_PRIORITY);
122 check_jvmti_error(jvmti, err, "running agent thread");
123 }
124
125 /* Callback for JVMTI_EVENT_GARBAGE_COLLECTION_START */
126 static void JNICALL
127 gc_start(jvmtiEnv* jvmti_env)
128 {
129 stdout_message("GarbageCollectionStart...\n");
130 }
131
132 /* Callback for JVMTI_EVENT_GARBAGE_COLLECTION_FINISH */
133 static void JNICALL
134 gc_finish(jvmtiEnv* jvmti_env)
135 {
136 jvmtiError err;
137
138 stdout_message("GarbageCollectionFinish...\n");
139
140 err = (*jvmti)->RawMonitorEnter(jvmti, lock);
141 check_jvmti_error(jvmti, err, "raw monitor enter");
142 gc_count++;
143 err = (*jvmti)->RawMonitorNotify(jvmti, lock);
144 check_jvmti_error(jvmti, err, "raw monitor notify");
145 err = (*jvmti)->RawMonitorExit(jvmti, lock);
146 check_jvmti_error(jvmti, err, "raw monitor exit");
147 }
148
149 /* Agent_OnLoad() is called first, we prepare for a VM_INIT event here. */
150 JNIEXPORT jint JNICALL
151 Agent_OnLoad(JavaVM *vm, char *options, void *reserved)
152 {
153 jint rc;
154 jvmtiError err;
155 jvmtiCapabilities capabilities;
156 jvmtiEventCallbacks callbacks;
157
158 /* Get JVMTI environment */
159 rc = (*vm)->GetEnv(vm, (void **)&jvmti, JVMTI_VERSION);
160 if (rc != JNI_OK) {
161 fatal_error("ERROR: Unable to create jvmtiEnv, rc=%d\n", rc);
162 return -1;
163 }
164
165 /* Get/Add JVMTI capabilities */
166 (void)memset(&capabilities, 0, sizeof(capabilities));
167 capabilities.can_generate_garbage_collection_events = 1;
168 err = (*jvmti)->AddCapabilities(jvmti, &capabilities);
169 check_jvmti_error(jvmti, err, "add capabilities");
170
171 /* Set callbacks and enable event notifications */
172 memset(&callbacks, 0, sizeof(callbacks));
173 callbacks.VMInit = &vm_init;
174 callbacks.GarbageCollectionStart = &gc_start;
175 callbacks.GarbageCollectionFinish = &gc_finish;
176 err = (*jvmti)->SetEventCallbacks(jvmti, &callbacks, sizeof(callbacks));
177 check_jvmti_error(jvmti, err, "set event callbacks");
178 err = (*jvmti)->SetEventNotificationMode(jvmti, JVMTI_ENABLE,
179 JVMTI_EVENT_VM_INIT, NULL);
180 check_jvmti_error(jvmti, err, "set event notification");
181 err = (*jvmti)->SetEventNotificationMode(jvmti, JVMTI_ENABLE,
182 JVMTI_EVENT_GARBAGE_COLLECTION_START, NULL);
183 check_jvmti_error(jvmti, err, "set event notification");
184 err = (*jvmti)->SetEventNotificationMode(jvmti, JVMTI_ENABLE,
185 JVMTI_EVENT_GARBAGE_COLLECTION_FINISH, NULL);
186 check_jvmti_error(jvmti, err, "set event notification");
187
188 /* Create the necessary raw monitor */
189 err = (*jvmti)->CreateRawMonitor(jvmti, "lock", &lock);
190 check_jvmti_error(jvmti, err, "create raw monitor");
191 return 0;
192 }
193
194 /* Agent_OnUnload() is called last */
195 JNIEXPORT void JNICALL
196 Agent_OnUnload(JavaVM *vm)
197 {
198 }