/*

 * 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);

    // NewWeakGlobalRef can throw OOM, clear exception here.

    if ((*env)->ExceptionCheck(env)) {

        (*env)->ExceptionClear(env);

        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.

         * It never throws OOM.

         * 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);

        // NewWeakGlobalRef can throw OOM, clear exception here.

        if ((*env)->ExceptionCheck(env)) {

            (*env)->ExceptionClear(env);

        }

        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);

                // NewLocalRef never throws OOM.

                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;