forked from openjdk/jdk11u-dev
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classTrack.c
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classTrack.c
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/*
* Copyright (c) 2001, 2022, 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. Oracle designates this
* particular file as subject to the "Classpath" exception as provided
* by Oracle in the LICENSE file that accompanied this code.
*
* 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.
*/
/*
* This module tracks classes that have been prepared, so as to
* be able to report which have been unloaded. On VM start-up
* and whenever new classes are loaded, all prepared classes'
* signatures are attached as JVMTI tag to the class object.
* Class unloading is tracked by registering
* ObjectFree callback on class objects. When this happens, we find
* the signature of the unloaded class(es) and report them back
* to the event handler to synthesize class-unload-events.
*/
#include "util.h"
#include "bag.h"
#include "classTrack.h"
#define NOT_TAGGED 0
/*
* The JVMTI tracking env to keep track of klass tags for class-unloads
*/
static jvmtiEnv* trackingEnv;
/*
* A bag containing all the deleted classes' signatures. Must be accessed under
* classTrackLock.
*/
struct bag* deletedSignatures;
/*
* Lock to keep integrity of deletedSignatures.
*/
static jrawMonitorID classTrackLock;
/*
* Invoke the callback when classes are freed, find and record the signature
* in deletedSignatures. Those are only used in addPreparedClass() by the
* same thread.
*/
static void JNICALL
cbTrackingObjectFree(jvmtiEnv* jvmti_env, jlong tag)
{
debugMonitorEnter(classTrackLock);
if (deletedSignatures == NULL) {
debugMonitorExit(classTrackLock);
return;
}
*(char**)bagAdd(deletedSignatures) = (char*)jlong_to_ptr(tag);
debugMonitorExit(classTrackLock);
}
/*
* Called after class unloads have occurred.
* The signatures of classes which were unloaded are returned.
*/
struct bag *
classTrack_processUnloads(JNIEnv *env)
{
if (deletedSignatures == NULL) {
return NULL;
}
/* Allocate new bag outside classTrackLock lock to avoid deadlock.
*
* Note: jvmtiAllocate/jvmtiDeallocate() may be blocked by ongoing safepoints.
* It is dangerous to call them (via bagCreateBag/bagDestroyBag()) while holding monitor(s),
* because jvmti may post events, e.g. JVMTI_EVENT_OBJECT_FREE at safepoints and event processing
* code may acquire the same monitor(s), e.g. classTrackLock in cbTrackingObjectFree(),
* which can lead to deadlock.
*/
struct bag* new_bag = bagCreateBag(sizeof(char*), 10);
debugMonitorEnter(classTrackLock);
struct bag* deleted = deletedSignatures;
deletedSignatures = new_bag;
debugMonitorExit(classTrackLock);
return deleted;
}
/*
* Add a class to the prepared class table.
*/
void
classTrack_addPreparedClass(JNIEnv *env_unused, jclass klass)
{
jvmtiError error;
jvmtiEnv* env = trackingEnv;
if (gdata && gdata->assertOn) {
// Check this is not already tagged.
jlong tag;
error = JVMTI_FUNC_PTR(trackingEnv, GetTag)(env, klass, &tag);
if (error != JVMTI_ERROR_NONE) {
EXIT_ERROR(error, "Unable to GetTag with class trackingEnv");
}
JDI_ASSERT(tag == NOT_TAGGED);
}
char* signature;
error = classSignature(klass, &signature, NULL);
if (error != JVMTI_ERROR_NONE) {
EXIT_ERROR(error,"signature");
}
error = JVMTI_FUNC_PTR(trackingEnv, SetTag)(env, klass, ptr_to_jlong(signature));
if (error != JVMTI_ERROR_NONE) {
jvmtiDeallocate(signature);
EXIT_ERROR(error,"SetTag");
}
}
static jboolean
setupEvents()
{
jvmtiCapabilities caps;
memset(&caps, 0, sizeof(caps));
caps.can_generate_object_free_events = 1;
jvmtiError error = JVMTI_FUNC_PTR(trackingEnv, AddCapabilities)(trackingEnv, &caps);
if (error != JVMTI_ERROR_NONE) {
return JNI_FALSE;
}
jvmtiEventCallbacks cb;
memset(&cb, 0, sizeof(cb));
cb.ObjectFree = cbTrackingObjectFree;
error = JVMTI_FUNC_PTR(trackingEnv, SetEventCallbacks)(trackingEnv, &cb, sizeof(cb));
if (error != JVMTI_ERROR_NONE) {
return JNI_FALSE;
}
error = JVMTI_FUNC_PTR(trackingEnv, SetEventNotificationMode)(trackingEnv, JVMTI_ENABLE, JVMTI_EVENT_OBJECT_FREE, NULL);
if (error != JVMTI_ERROR_NONE) {
return JNI_FALSE;
}
return JNI_TRUE;
}
/*
* Called once to initialize class-tracking.
*/
void
classTrack_initialize(JNIEnv *env)
{
deletedSignatures = NULL;
classTrackLock = debugMonitorCreate("Deleted class tag lock");
trackingEnv = getSpecialJvmti();
if (trackingEnv == NULL) {
EXIT_ERROR(AGENT_ERROR_INTERNAL, "Failed to allocate tag-tracking jvmtiEnv");
}
if (!setupEvents()) {
EXIT_ERROR(AGENT_ERROR_INTERNAL, "Unable to setup ObjectFree tracking");
}
jint classCount;
jclass *classes;
jvmtiError error;
jint i;
error = allLoadedClasses(&classes, &classCount);
if ( error == JVMTI_ERROR_NONE ) {
for (i = 0; i < classCount; i++) {
jclass klass = classes[i];
jint status;
jint wanted = JVMTI_CLASS_STATUS_PREPARED | JVMTI_CLASS_STATUS_ARRAY;
status = classStatus(klass);
if ((status & wanted) != 0) {
classTrack_addPreparedClass(env, klass);
}
}
jvmtiDeallocate(classes);
} else {
EXIT_ERROR(error,"loaded classes array");
}
}
/*
* Called to activate class-tracking when a listener registers for EI_GC_FINISH.
*/
void
classTrack_activate(JNIEnv *env)
{
// Allocate bag outside classTrackLock lock to avoid deadlock.
// See comments in classTrack_processUnloads() for details.
struct bag* new_bag = bagCreateBag(sizeof(char*), 1000);
debugMonitorEnter(classTrackLock);
deletedSignatures = new_bag;
debugMonitorExit(classTrackLock);
}
static jboolean
cleanDeleted(void *signatureVoid, void *arg)
{
char* sig = *(char**)signatureVoid;
jvmtiDeallocate(sig);
return JNI_TRUE;
}
/*
* Called when agent detaches.
*/
void
classTrack_reset(void)
{
debugMonitorEnter(classTrackLock);
struct bag* to_delete = deletedSignatures;
deletedSignatures = NULL;
debugMonitorExit(classTrackLock);
// Deallocate bag outside classTrackLock to avoid deadlock.
// See comments in classTrack_processUnloads() for details.
if (to_delete != NULL) {
bagEnumerateOver(to_delete, cleanDeleted, NULL);
bagDestroyBag(to_delete);
}
}