/*
* Copyright (c) 1998, 2013, 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.
*/
#if defined(_ALLBSD_SOURCE)
#include <stdint.h> /* for uintptr_t */
#endif
#include "util.h"
#include "commonRef.h"
#define ALL_REFS -1
/*
* Each object sent to the front end is tracked with the RefNode struct
* (see util.h).
* External to this module, objects are identified by a jlong id which is
* simply the sequence number. A weak reference is usually used so that
* the presence of a debugger-tracked object will not prevent
* its collection. Once an object is collected, its RefNode may be
* deleted and the weak ref inside may be reused (these may happen in
* either order). Using the sequence number
* as the object id prevents ambiguity in the object id when the weak ref
* is reused. The RefNode* is stored with the object as it's JVMTI Tag.
*
* The ref member is changed from weak to strong when
* gc of the object is to be prevented.
* Whether or not it is strong, it is never exported from this module.
*
* A reference count of each jobject is also maintained here. It tracks
* the number times an object has been referenced through
* commonRef_refToID. A RefNode is freed once the reference
* count is decremented to 0 (with commonRef_release*), even if the
* corresponding object has not been collected.
*
* One hash table is maintained. The mapping of ID to jobject (or RefNode*)
* is handled with one hash table that will re-size itself as the number
* of RefNode's grow.
*/
/* Initial hash table size (must be power of 2) */
#define HASH_INIT_SIZE 512
/* If element count exceeds HASH_EXPAND_SCALE*hash_size we expand & re-hash */
#define HASH_EXPAND_SCALE 8
/* Maximum hash table size (must be power of 2) */
#define HASH_MAX_SIZE (1024*HASH_INIT_SIZE)
/* Map a key (ID) to a hash bucket */
static jint
hashBucket(jlong key)
{
/* Size should always be a power of 2, use mask instead of mod operator */
/*LINTED*/
return ((jint)key) & (gdata->objectsByIDsize-1);
}
/* Generate a new ID */
static jlong
newSeqNum(void)
{
return gdata->nextSeqNum++;
}
/* Create a fresh RefNode structure, create a weak ref and tag the object */
static RefNode *
createNode(JNIEnv *env, jobject ref)
{
RefNode *node;
jobject weakRef;
jvmtiError error;
/* Could allocate RefNode's in blocks, not sure it would help much */
node = (RefNode*)jvmtiAllocate((int)sizeof(RefNode));
if (node == NULL) {
return NULL;
}
/* Create weak reference to make sure we have a reference */
weakRef = JNI_FUNC_PTR(env,NewWeakGlobalRef)(env, ref);
if (weakRef == NULL) {
jvmtiDeallocate(node);
return NULL;
}
/* Set tag on weakRef */
error = JVMTI_FUNC_PTR(gdata->jvmti, SetTag)
(gdata->jvmti, weakRef, ptr_to_jlong(node));
if ( error != JVMTI_ERROR_NONE ) {
JNI_FUNC_PTR(env,DeleteWeakGlobalRef)(env, weakRef);
jvmtiDeallocate(node);
return NULL;
}
/* Fill in RefNode */
node->ref = weakRef;
node->isStrong = JNI_FALSE;
node->count = 1;
node->seqNum = newSeqNum();
/* Count RefNode's created */
gdata->objectsByIDcount++;
return node;
}
/* Delete a RefNode allocation, delete weak/global ref and clear tag */
static void
deleteNode(JNIEnv *env, RefNode *node)
{
LOG_MISC(("Freeing %d (%x)\n", (int)node->seqNum, node->ref));
if ( node->ref != NULL ) {
/* Clear tag */
(void)JVMTI_FUNC_PTR(gdata->jvmti,SetTag)
(gdata->jvmti, node->ref, NULL_OBJECT_ID);
if (node->isStrong) {
JNI_FUNC_PTR(env,DeleteGlobalRef)(env, node->ref);
} else {
JNI_FUNC_PTR(env,DeleteWeakGlobalRef)(env, node->ref);
}
}
gdata->objectsByIDcount--;
jvmtiDeallocate(node);
}
/* Change a RefNode to have a strong reference */
static jobject
strengthenNode(JNIEnv *env, RefNode *node)
{
if (!node->isStrong) {
jobject strongRef;
strongRef = JNI_FUNC_PTR(env,NewGlobalRef)(env, node->ref);
/*
* NewGlobalRef on a weak ref will return NULL if the weak
* reference has been collected or if out of memory.
* We need to distinguish those two occurrences.
*/
if ((strongRef == NULL) && !isSameObject(env, node->ref, NULL)) {
EXIT_ERROR(AGENT_ERROR_NULL_POINTER,"NewGlobalRef");
}
if (strongRef != NULL) {
JNI_FUNC_PTR(env,DeleteWeakGlobalRef)(env, node->ref);
node->ref = strongRef;
node->isStrong = JNI_TRUE;
}
return strongRef;
} else {
return node->ref;
}
}
/* Change a RefNode to have a weak reference */
static jweak
weakenNode(JNIEnv *env, RefNode *node)
{
if (node->isStrong) {
jweak weakRef;
weakRef = JNI_FUNC_PTR(env,NewWeakGlobalRef)(env, node->ref);
if (weakRef != NULL) {
JNI_FUNC_PTR(env,DeleteGlobalRef)(env, node->ref);
node->ref = weakRef;
node->isStrong = JNI_FALSE;
}
return weakRef;
} else {
return node->ref;
}
}
/*
* Returns the node which contains the common reference for the
* given object. The passed reference should not be a weak reference
* managed in the object hash table (i.e. returned by commonRef_idToRef)
* because no sequence number checking is done.
*/
static RefNode *
findNodeByRef(JNIEnv *env, jobject ref)
{
jvmtiError error;
jlong tag;
tag = NULL_OBJECT_ID;
error = JVMTI_FUNC_PTR(gdata->jvmti,GetTag)(gdata->jvmti, ref, &tag);
if ( error == JVMTI_ERROR_NONE ) {
RefNode *node;
node = (RefNode*)jlong_to_ptr(tag);
return node;
}
return NULL;
}
/* Locate and delete a node based on ID */
static void
deleteNodeByID(JNIEnv *env, jlong id, jint refCount)
{
jint slot;
RefNode *node;
RefNode *prev;
slot = hashBucket(id);
node = gdata->objectsByID[slot];
prev = NULL;
while (node != NULL) {
if (id == node->seqNum) {
if (refCount != ALL_REFS) {
node->count -= refCount;
} else {
node->count = 0;
}
if (node->count <= 0) {
if ( node->count < 0 ) {
EXIT_ERROR(AGENT_ERROR_INTERNAL,"RefNode count < 0");
}
/* Detach from id hash table */
if (prev == NULL) {
gdata->objectsByID[slot] = node->next;
} else {
prev->next = node->next;
}
deleteNode(env, node);
}
break;
}
prev = node;
node = node->next;
}
}
/*
* Returns the node stored in the object hash table for the given object
* id. The id should be a value previously returned by
* commonRef_refToID.
*
* NOTE: It is possible that a match is found here, but that the object
* is garbage collected by the time the caller inspects node->ref.
* Callers should take care using the node->ref object returned here.
*
*/
static RefNode *
findNodeByID(JNIEnv *env, jlong id)
{
jint slot;
RefNode *node;
RefNode *prev;
slot = hashBucket(id);
node = gdata->objectsByID[slot];
prev = NULL;
while (node != NULL) {
if ( id == node->seqNum ) {
if ( prev != NULL ) {
/* Re-order hash list so this one is up front */
prev->next = node->next;
node->next = gdata->objectsByID[slot];
gdata->objectsByID[slot] = node;
}
break;
}
node = node->next;
}
return node;
}
/* Initialize the hash table stored in gdata area */
static void
initializeObjectsByID(int size)
{
/* Size should always be a power of 2 */
if ( size > HASH_MAX_SIZE ) size = HASH_MAX_SIZE;
gdata->objectsByIDsize = size;
gdata->objectsByIDcount = 0;
gdata->objectsByID = (RefNode**)jvmtiAllocate((int)sizeof(RefNode*)*size);
(void)memset(gdata->objectsByID, 0, (int)sizeof(RefNode*)*size);
}
/* hash in a RefNode */
static void
hashIn(RefNode *node)
{
jint slot;
/* Add to id hashtable */
slot = hashBucket(node->seqNum);
node->next = gdata->objectsByID[slot];
gdata->objectsByID[slot] = node;
}
/* Allocate and add RefNode to hash table */
static RefNode *
newCommonRef(JNIEnv *env, jobject ref)
{
RefNode *node;
/* Allocate the node and set it up */
node = createNode(env, ref);
if ( node == NULL ) {
return NULL;
}
/* See if hash table needs expansion */
if ( gdata->objectsByIDcount > gdata->objectsByIDsize*HASH_EXPAND_SCALE &&
gdata->objectsByIDsize < HASH_MAX_SIZE ) {
RefNode **old;
int oldsize;
int newsize;
int i;
/* Save old information */
old = gdata->objectsByID;
oldsize = gdata->objectsByIDsize;
/* Allocate new hash table */
gdata->objectsByID = NULL;
newsize = oldsize*HASH_EXPAND_SCALE;
if ( newsize > HASH_MAX_SIZE ) newsize = HASH_MAX_SIZE;
initializeObjectsByID(newsize);
/* Walk over old one and hash in all the RefNodes */
for ( i = 0 ; i < oldsize ; i++ ) {
RefNode *onode;
onode = old[i];
while (onode != NULL) {
RefNode *next;
next = onode->next;
hashIn(onode);
onode = next;
}
}
jvmtiDeallocate(old);
}
/* Add to id hashtable */
hashIn(node);
return node;
}
/* Initialize the commonRefs usage */
void
commonRef_initialize(void)
{
gdata->refLock = debugMonitorCreate("JDWP Reference Table Monitor");
gdata->nextSeqNum = 1; /* 0 used for error indication */
initializeObjectsByID(HASH_INIT_SIZE);
}
/* Reset the commonRefs usage */
void
commonRef_reset(JNIEnv *env)
{
debugMonitorEnter(gdata->refLock); {
int i;
for (i = 0; i < gdata->objectsByIDsize; i++) {
RefNode *node;
node = gdata->objectsByID[i];
while (node != NULL) {
RefNode *next;
next = node->next;
deleteNode(env, node);
node = next;
}
gdata->objectsByID[i] = NULL;
}
/* Toss entire hash table and re-create a new one */
jvmtiDeallocate(gdata->objectsByID);
gdata->objectsByID = NULL;
gdata->nextSeqNum = 1; /* 0 used for error indication */
initializeObjectsByID(HASH_INIT_SIZE);
} debugMonitorExit(gdata->refLock);
}
/*
* Given a reference obtained from JNI or JVMTI, return an object
* id suitable for sending to the debugger front end.
*/
jlong
commonRef_refToID(JNIEnv *env, jobject ref)
{
jlong id;
if (ref == NULL) {
return NULL_OBJECT_ID;
}
id = NULL_OBJECT_ID;
debugMonitorEnter(gdata->refLock); {
RefNode *node;
node = findNodeByRef(env, ref);
if (node == NULL) {
node = newCommonRef(env, ref);
if ( node != NULL ) {
id = node->seqNum;
}
} else {
id = node->seqNum;
node->count++;
}
} debugMonitorExit(gdata->refLock);
return id;
}
/*
* Given an object ID obtained from the debugger front end, return a
* strong, global reference to that object (or NULL if the object
* has been collected). The reference can then be used for JNI and
* JVMTI calls. Caller is resposible for deleting the returned reference.
*/
jobject
commonRef_idToRef(JNIEnv *env, jlong id)
{
jobject ref;
ref = NULL;
debugMonitorEnter(gdata->refLock); {
RefNode *node;
node = findNodeByID(env, id);
if (node != NULL) {
if (node->isStrong) {
saveGlobalRef(env, node->ref, &ref);
} else {
jobject lref;
lref = JNI_FUNC_PTR(env,NewLocalRef)(env, node->ref);
if ( lref == NULL ) {
/* Object was GC'd shortly after we found the node */
deleteNodeByID(env, node->seqNum, ALL_REFS);
} else {
saveGlobalRef(env, node->ref, &ref);
JNI_FUNC_PTR(env,DeleteLocalRef)(env, lref);
}
}
}
} debugMonitorExit(gdata->refLock);
return ref;
}
/* Deletes the global reference that commonRef_idToRef() created */
void
commonRef_idToRef_delete(JNIEnv *env, jobject ref)
{
if ( ref==NULL ) {
return;
}
tossGlobalRef(env, &ref);
}
/* Prevent garbage collection of an object */
jvmtiError
commonRef_pin(jlong id)
{
jvmtiError error;
error = JVMTI_ERROR_NONE;
if (id == NULL_OBJECT_ID) {
return error;
}
debugMonitorEnter(gdata->refLock); {
JNIEnv *env;
RefNode *node;
env = getEnv();
node = findNodeByID(env, id);
if (node == NULL) {
error = AGENT_ERROR_INVALID_OBJECT;
} else {
jobject strongRef;
strongRef = strengthenNode(env, node);
if (strongRef == NULL) {
/*
* Referent has been collected, clean up now.
*/
error = AGENT_ERROR_INVALID_OBJECT;
deleteNodeByID(env, id, ALL_REFS);
}
}
} debugMonitorExit(gdata->refLock);
return error;
}
/* Permit garbage collection of an object */
jvmtiError
commonRef_unpin(jlong id)
{
jvmtiError error;
error = JVMTI_ERROR_NONE;
debugMonitorEnter(gdata->refLock); {
JNIEnv *env;
RefNode *node;
env = getEnv();
node = findNodeByID(env, id);
if (node != NULL) {
jweak weakRef;
weakRef = weakenNode(env, node);
if (weakRef == NULL) {
error = AGENT_ERROR_OUT_OF_MEMORY;
}
}
} debugMonitorExit(gdata->refLock);
return error;
}
/* Release tracking of an object by ID */
void
commonRef_release(JNIEnv *env, jlong id)
{
debugMonitorEnter(gdata->refLock); {
deleteNodeByID(env, id, 1);
} debugMonitorExit(gdata->refLock);
}
void
commonRef_releaseMultiple(JNIEnv *env, jlong id, jint refCount)
{
debugMonitorEnter(gdata->refLock); {
deleteNodeByID(env, id, refCount);
} debugMonitorExit(gdata->refLock);
}
/* Get rid of RefNodes for objects that no longer exist */
void
commonRef_compact(void)
{
JNIEnv *env;
RefNode *node;
RefNode *prev;
int i;
env = getEnv();
debugMonitorEnter(gdata->refLock); {
if ( gdata->objectsByIDsize > 0 ) {
/*
* Walk through the id-based hash table. Detach any nodes
* for which the ref has been collected.
*/
for (i = 0; i < gdata->objectsByIDsize; i++) {
node = gdata->objectsByID[i];
prev = NULL;
while (node != NULL) {
/* Has the object been collected? */
if ( (!node->isStrong) &&
isSameObject(env, node->ref, NULL)) {
RefNode *freed;
/* Detach from the ID list */
if (prev == NULL) {
gdata->objectsByID[i] = node->next;
} else {
prev->next = node->next;
}
freed = node;
node = node->next;
deleteNode(env, freed);
} else {
prev = node;
node = node->next;
}
}
}
}
} debugMonitorExit(gdata->refLock);
}
/* Lock the commonRef tables */
void
commonRef_lock(void)
{
debugMonitorEnter(gdata->refLock);
}
/* Unlock the commonRef tables */
void
commonRef_unlock(void)
{
debugMonitorExit(gdata->refLock);
}