/*
* Copyright (c) 2001, 2005, 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 compute which have been unloaded. On VM start-up
* all prepared classes are put in a table. As class prepare
* events come in they are added to the table. After an unload
* event or series of them, the VM can be asked for the list
* of classes; this list is compared against the table keep by
* this module, any classes no longer present are known to
* have been unloaded.
*
* ANDROID-CHANGED: This module is almost totally re-written
* for android. On android, we have a limited number of jweak
* references that can be around at any one time. In order to
* preserve this limited resource for user-code use we keep
* track of the status of classes using JVMTI tags.
*
* We keep a linked-list of the signatures of loaded classes
* associated with the tag we gave to that class. The tag is
* simply incremented every time we add a new class.
*
* We also request (on the separate tracking jvmtiEnv) an
* ObjectFree event be called for each of these classes. This
* allows us to keep a running list of all the classes known to
* have been collected since the last call to
* classTrack_processUnloads. On each call to processUnloads we
* iterate through this list and remove from the main list all
* the objects that have been collected. We then return a list of
* the class-signatures that have been collected.
*
* For efficiency and simplicity we don't bother retagging or
* re-using old tags, instead relying on the fact that no
* program will ever be able to exhaust the (2^64 - 1) possible
* tag values (which would require that many class-loads).
*
* This relies on the tagging and ObjectFree implementation being
* relatively efficient for performance. It has the advantage of
* not requiring any jweaks.
*
* All calls into any function of this module must be either
* done before the event-handler system is setup or done while
* holding the event handlerLock. The list of freed classes is
* protected by the classTagLock.
*/
#include "util.h"
#include "bag.h"
#include "classTrack.h"
typedef struct KlassNode {
jlong klass_tag; /* Tag the klass has in the tracking-env */
char *signature; /* class signature */
struct KlassNode *next; /* next node in this slot */
} KlassNode;
/*
* pointer to first node of a linked list of prepared classes KlassNodes.
*/
static KlassNode *list;
/*
* The JVMTI env we use to keep track of klass tags which allows us to detect class-unloads.
*/
static jvmtiEnv *trackingEnv;
/*
* The current highest tag number in use by the trackingEnv.
*
* No need for synchronization since everything is done under the handlerLock.
*/
static jlong currentKlassTag;
/*
* A lock to protect access to 'deletedTagBag'
*/
static jrawMonitorID deletedTagLock;
/*
* A bag containing all the deleted klass_tags ids. This must be accessed under the
* deletedTagLock.
*
* It is cleared each time classTrack_processUnloads is called.
*/
struct bag* deletedTagBag;
/*
* The callback for when classes are freed. Only classes are called because this is registered with
* the trackingEnv which only tags classes.
*/
static void JNICALL
cbTrackingObjectFree(jvmtiEnv* jvmti_env, jlong tag)
{
debugMonitorEnter(deletedTagLock);
*(jlong*)bagAdd(deletedTagBag) = tag;
debugMonitorExit(deletedTagLock);
}
/*
* Returns true (thus continuing the iteration) if the item is not the searched for tag.
*/
static jboolean
isNotTag(void* item, void* needle)
{
return *(jlong*)item != *(jlong*)needle;
}
/*
* This requires that deletedTagLock and the handlerLock are both held.
*/
static jboolean
isClassUnloaded(jlong tag)
{
/* bagEnumerateOver returns true if 'func' returns true on all items and aborts early if not. */
return !bagEnumerateOver(deletedTagBag, isNotTag, &tag);
}
/*
* Called after class unloads have occurred. Creates a new hash table
* of currently loaded prepared classes.
* The signatures of classes which were unloaded (not present in the
* new table) are returned.
*
* NB This relies on addPreparedClass being called for every class loaded after the
* classTrack_initialize function is called. We will not request all loaded classes again after
* that. It also relies on not being called concurrently with any classTrack_addPreparedClass or
* other classTrack_processUnloads calls.
*/
struct bag *
classTrack_processUnloads(JNIEnv *env)
{
/* We could optimize this somewhat by holding the deletedTagLock for a much shorter time,
* replacing it as soon as we enter and then destroying it once we are done with it. This will
* cause a lot of memory churn and this function is not expected to be called that often.
* Furthermore due to the check for an empty bag (which should be very common) normally this
* will finish very quickly. In cases where there is a concurrent GC occuring and a class is
* being collected the GC-ing threads could be blocked until we are done but this is expected to
* be very rare.
*/
debugMonitorEnter(deletedTagLock);
/* Take and return the deletedTagBag */
struct bag* deleted = bagCreateBag(sizeof(char*), bagSize(deletedTagBag));
/* The deletedTagBag is going to be much shorter than the klassNode list so we should walk the
* KlassNode list once and scan the deletedTagBag each time. We only need to this in the rare
* case that there was anything deleted though.
*/
if (bagSize(deletedTagBag) != 0) {
KlassNode* node = list;
KlassNode** previousNext = &list;
while (node != NULL) {
if (isClassUnloaded(node->klass_tag)) {
/* Update the previous node's next pointer to point after this node. Note that we
* update the value pointed to by previousNext but not the value of previousNext
* itself.
*/
*previousNext = node->next;
/* Put this nodes signature into the deleted bag */
*(char**)bagAdd(deleted) = node->signature;
/* Deallocate the node */
jvmtiDeallocate(node);
} else {
/* This node will become the previous node so update the previousNext pointer to
* this nodes next pointer.
*/
previousNext = &(node->next);
}
node = *previousNext;
}
bagDeleteAll(deletedTagBag);
}
debugMonitorExit(deletedTagLock);
return deleted;
}
/*
* Add a class to the prepared class list.
* Assumes no duplicates.
*/
void
classTrack_addPreparedClass(JNIEnv *env, jclass klass)
{
KlassNode *node;
jvmtiError error;
if (gdata->assertOn) {
/* Check this is not a duplicate */
jlong tag;
error = JVMTI_FUNC_PTR(trackingEnv,GetTag)(trackingEnv, klass, &tag);
if (error != JVMTI_ERROR_NONE) {
EXIT_ERROR(error,"unable to get-tag with class trackingEnv!");
}
if (tag != 0l) {
JDI_ASSERT_FAILED("Attempting to insert duplicate class");
}
}
node = jvmtiAllocate(sizeof(KlassNode));
if (node == NULL) {
EXIT_ERROR(AGENT_ERROR_OUT_OF_MEMORY,"KlassNode");
}
error = classSignature(klass, &(node->signature), NULL);
if (error != JVMTI_ERROR_NONE) {
jvmtiDeallocate(node);
EXIT_ERROR(error,"signature");
}
node->klass_tag = ++currentKlassTag;
error = JVMTI_FUNC_PTR(trackingEnv,SetTag)(trackingEnv, klass, node->klass_tag);
if (error != JVMTI_ERROR_NONE) {
jvmtiDeallocate(node->signature);
jvmtiDeallocate(node);
EXIT_ERROR(error,"SetTag");
}
/* Insert the new node */
node->next = list;
list = node;
}
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 build the initial prepared class hash table.
*/
void
classTrack_initialize(JNIEnv *env)
{
/* ANDROID_CHANGED: Setup the tracking env and the currentKlassTag */
trackingEnv = getSpecialJvmti();
if ( trackingEnv == NULL ) {
EXIT_ERROR(AGENT_ERROR_INTERNAL,"Failed to allocate tag-tracking jvmtiEnv");
}
/* We want to create these before turning on the events or tagging anything. */
deletedTagLock = debugMonitorCreate("Deleted class tag lock");
deletedTagBag = bagCreateBag(sizeof(jlong), 10);
/* ANDROID-CHANGED: Setup the trackingEnv's ObjectFree event */
if (!setupEvents()) {
/* On android classes are usually not unloaded too often so this is not a huge loss. */
ERROR_MESSAGE(("Unable to setup class ObjectFree tracking! Class unloads will not "
"be reported!"));
}
currentKlassTag = 0l;
list = NULL;
WITH_LOCAL_REFS(env, 1) {
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);
/* We only want prepared classes and arrays */
status = classStatus(klass);
if ( (status & wanted) != 0 ) {
classTrack_addPreparedClass(env, klass);
}
}
jvmtiDeallocate(classes);
} else {
EXIT_ERROR(error,"loaded classes array");
}
} END_WITH_LOCAL_REFS(env)
}
void
classTrack_reset(void)
{
}