src/main/cpp/edu_stanford_ramcloud_JRamCloud.cc

/* Copyright (c) 2013 Stanford University
 *
 * Permission to use, copy, modify, and distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR(S) DISCLAIM ALL WARRANTIES
 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL AUTHORS BE LIABLE FOR
 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 */

#include <RamCloud.h>
#include <TableEnumerator.h>
#include <Object.h>
#include "edu_stanford_ramcloud_JRamCloud.h"
#include "edu_stanford_ramcloud_JRamCloud_TableEnumerator.h"

using namespace RAMCloud;

/// Our JRamCloud java library is packaged under "edu.stanford.ramcloud".
/// We will need this when using FindClass, etc.
#define PACKAGE_PATH "edu/stanford/ramcloud/"

#define check_null(var, msg)                                                \
    if (var == NULL) {                                                      \
        throw Exception(HERE, "JRamCloud: NULL returned: " msg "\n");       \
    }

/**
 * This class provides a simple means of extracting C-style strings
 * from a jstring and cleans up when the destructor is called. This
 * avoids having to manually do the annoying GetStringUTFChars /
 * ReleaseStringUTFChars dance. 
 */
class JStringGetter {
  public:
    JStringGetter(JNIEnv* env, jstring jString)
        : env(env)
        , jString(jString)
        , string(env->GetStringUTFChars(jString, 0))
    {
        check_null(string, "GetStringUTFChars failed");
    }
    
    ~JStringGetter()
    {
        if (string != NULL)
            env->ReleaseStringUTFChars(jString, string);
    }

  private:    
    JNIEnv* env;
    jstring jString;

  public:
    const char* const string;
};

/**
 * This class provides a simple means of accessing jbyteArrays as
 * C-style void* buffers and cleans up when the destructor is called.
 * This avoids having to manually do the annoying GetByteArrayElements /
 * ReleaseByteArrayElements dance.
 */
class JByteArrayGetter {
  public:
    JByteArrayGetter(JNIEnv* env, jbyteArray jByteArray)
        : env(env)
        , jByteArray(jByteArray)
        , pointer(static_cast<void*>(env->GetByteArrayElements(jByteArray, 0)))
        , length(env->GetArrayLength(jByteArray))
    {
        check_null(pointer, "GetByteArrayElements failed");
    }
    
    ~JByteArrayGetter()
    {
        if (pointer != NULL) {
            env->ReleaseByteArrayElements(jByteArray,
                                          reinterpret_cast<jbyte*>(pointer),
                                          0);
        }
    }

  private:    
    JNIEnv* env;
    jbyteArray jByteArray;

  public:
    void* const pointer;
    const jsize length;
};

class JByteArrayReference {
  public:
    JByteArrayReference(JNIEnv* env, jbyteArray jByteArray)
        : env(env)
        , jByteArray(jByteArray)
        , pointer(static_cast<const void*>(env->GetByteArrayElements(jByteArray, 0)))
        , length(env->GetArrayLength(jByteArray))
    {
        check_null(pointer, "GetByteArrayElements failed");
    }

    ~JByteArrayReference()
    {
        if (pointer != NULL) {
            env->ReleaseByteArrayElements(jByteArray,
                                          (jbyte*)pointer,
                                          JNI_ABORT);
        }
    }

  private:
    JNIEnv* env;
    jbyteArray jByteArray;

  public:
    const void* const pointer;
    const jsize length;
};

static RamCloud*
getRamCloud(JNIEnv* env, jobject jRamCloud)
{
    const static jclass cls = (jclass)env->NewGlobalRef(env->FindClass(PACKAGE_PATH "JRamCloud"));
    const static jfieldID fieldId = env->GetFieldID(cls, "ramcloudObjectPointer", "J");
    return reinterpret_cast<RamCloud*>(env->GetLongField(jRamCloud, fieldId));
}

static TableEnumerator*
getTableEnumerator(JNIEnv* env, jobject jTableEnumerator)
{
    const static jclass cls = (jclass)env->NewGlobalRef(env->FindClass(PACKAGE_PATH "JRamCloud$TableEnumerator"));
    const static jfieldID fieldId = env->GetFieldID(cls, "tableEnumeratorObjectPointer", "J");
    return reinterpret_cast<TableEnumerator*>(env->GetLongField(jTableEnumerator, fieldId));    
}

static void
createException(JNIEnv* env, jobject jRamCloud, const char* name)
{
    // Need to specify the full class name, including the package. To make it
    // slightly more complicated, our exceptions are nested under the JRamCloud
    // class.
    string fullName = PACKAGE_PATH;
    fullName += "JRamCloud$";
    fullName += name;

    // This would be much easier if we didn't make our Exception classes nested
    // under JRamCloud since env->ThrowNew() could be used instead. The problem
    // is that ThrowNew assumes a particular method signature that happens to
    // be incompatible with the nested classes' signatures.
    jclass cls = env->FindClass(fullName.c_str());
    check_null(cls, "FindClass failed");

    jmethodID methodId = env->GetMethodID(cls,
                                          "<init>",
                                          "(L" PACKAGE_PATH "JRamCloud;Ljava/lang/String;)V");
    check_null(methodId, "GetMethodID failed");

    jstring jString = env->NewStringUTF("");
    check_null(jString, "NewStringUTF failed");

    jthrowable exception = reinterpret_cast<jthrowable>(
        env->NewObject(cls, methodId, jRamCloud, jString));
    check_null(exception, "NewObject failed");

    env->Throw(exception);
}

/**
 * This macro is used to catch C++ exceptions and convert them into Java
 * exceptions. Be sure to wrap the individual RamCloud:: calls in try blocks,
 * rather than the entire methods, since doing so with functions that return
 * non-void is a bad idea with undefined(?) behaviour. 
 *
 * _returnValue is the value that should be returned from the JNI function
 * when an exception is caught and generated in Java. As far as I can tell,
 * the exception fires immediately upon returning from the JNI method. I
 * don't think anything else would make sense, but the JNI docs kind of
 * suck.
 */
#define EXCEPTION_CATCHER(_returnValue)                                        \
    catch (TableDoesntExistException& e) {                                     \
        createException(env, jRamCloud, "TableDoesntExistException");          \
        return _returnValue;                                                   \
    } catch (ObjectDoesntExistException& e) {                                  \
        createException(env, jRamCloud, "ObjectDoesntExistException");         \
        return _returnValue;                                                   \
    } catch (ObjectExistsException& e) {                                       \
        createException(env, jRamCloud, "ObjectExistsException");              \
        return _returnValue;                                                   \
    } catch (WrongVersionException& e) {                                       \
        createException(env, jRamCloud, "WrongVersionException");              \
        return _returnValue;                                                   \
    } catch (RejectRulesException& e) {                                        \
        createException(env, jRamCloud, "RejectRulesException");               \
        return _returnValue;                                                   \
    } catch (InvalidObjectException& e) {                                      \
        createException(env, jRamCloud, "InvalidObjectException");             \
        return _returnValue;                                                   \
    }

/*
 * Class:     edu_stanford_ramcloud_JRamCloud
 * Method:    connect
 * Signature: (Ljava/lang/String;)J
 */
JNIEXPORT jlong 
JNICALL Java_edu_stanford_ramcloud_JRamCloud_connect(JNIEnv *env,
                               jclass jRamCloud,
                               jstring coordinatorLocator)
{
    JStringGetter locator(env, coordinatorLocator);
    RamCloud* ramcloud = NULL;
    try {
        ramcloud = new RamCloud(locator.string);
    } EXCEPTION_CATCHER(NULL);
    return reinterpret_cast<jlong>(ramcloud);
}

/*
 * Class:     edu_stanford_ramcloud_JRamCloud
 * Method:    disconnect
 * Signature: (J)V
 */
JNIEXPORT void
JNICALL Java_edu_stanford_ramcloud_JRamCloud_disconnect(JNIEnv *env,
                                  jclass jRamCloud,
                                  jlong ramcloudObjectPointer)
{
    delete reinterpret_cast<RamCloud*>(ramcloudObjectPointer);
}

/*
 * Class:     edu_stanford_ramcloud_JRamCloud
 * Method:    createTable
 * Signature: (Ljava/lang/String;)I
 */
JNIEXPORT jlong
JNICALL Java_edu_stanford_ramcloud_JRamCloud_createTable__Ljava_lang_String_2(JNIEnv *env,
                                                        jobject jRamCloud,
                                                        jstring jTableName)
{
    return Java_edu_stanford_ramcloud_JRamCloud_createTable__Ljava_lang_String_2I(env,
                                                            jRamCloud,
                                                            jTableName,
                                                            1);
}

/*
 * Class:     edu_stanford_ramcloud_JRamCloud
 * Method:    createTable
 * Signature: (Ljava/lang/String;I)I
 */
JNIEXPORT jlong
JNICALL Java_edu_stanford_ramcloud_JRamCloud_createTable__Ljava_lang_String_2I(JNIEnv *env,
                                                         jobject jRamCloud,
                                                         jstring jTableName,
                                                         jint jServerSpan)
{
    RamCloud* ramcloud = getRamCloud(env, jRamCloud);
    JStringGetter tableName(env, jTableName);
    uint64_t tableId;
    try {
        tableId = ramcloud->createTable(tableName.string, jServerSpan);
    } EXCEPTION_CATCHER(-1);
    return static_cast<jlong>(tableId);
}

/*
 * Class:     edu_stanford_ramcloud_JRamCloud
 * Method:    dropTable
 * Signature: (Ljava/lang/String;)I
 */
JNIEXPORT void
JNICALL Java_edu_stanford_ramcloud_JRamCloud_dropTable(JNIEnv *env,
                                 jobject jRamCloud,
                                 jstring jTableName)
{
    RamCloud* ramcloud = getRamCloud(env, jRamCloud);
    JStringGetter tableName(env, jTableName);
    try {
        ramcloud->dropTable(tableName.string);
    } EXCEPTION_CATCHER();
}

/*
 * Class:     edu_stanford_ramcloud_JRamCloud
 * Method:    getTableId
 * Signature: (Ljava/lang/String;)J
 */
JNIEXPORT jlong
JNICALL Java_edu_stanford_ramcloud_JRamCloud_getTableId(JNIEnv *env,
                                  jobject jRamCloud,
                                  jstring jTableName)
{
    RamCloud* ramcloud = getRamCloud(env, jRamCloud);
    JStringGetter tableName(env, jTableName);
    uint64_t tableId;
    try {
        tableId = ramcloud->getTableId(tableName.string);
    } EXCEPTION_CATCHER(-1);
    return tableId;
}

/*
 * Class:     edu_stanford_ramcloud_JRamCloud
 * Method:    read
 * Signature: (J[B)LJRamCloud/Object;
 */
JNIEXPORT jobject
JNICALL Java_edu_stanford_ramcloud_JRamCloud_read__J_3B(JNIEnv *env,
                                  jobject jRamCloud,
                                  jlong jTableId,
                                  jbyteArray jKey)
{
    RamCloud* ramcloud = getRamCloud(env, jRamCloud);
    JByteArrayReference key(env, jKey);

    Buffer buffer;
    uint64_t version;
    try {
        ramcloud->read(jTableId, key.pointer, key.length, &buffer, NULL, &version);
    } EXCEPTION_CATCHER(NULL);

    jbyteArray jValue = env->NewByteArray(buffer.getTotalLength());
    check_null(jValue, "NewByteArray failed");
    JByteArrayGetter value(env, jValue);
    buffer.copy(0, buffer.getTotalLength(), value.pointer);

    // Note that using 'javap -s' on the class file will print out the method
    // signatures (the third argument to GetMethodID).
    const static jclass cls = (jclass)env->NewGlobalRef(env->FindClass(PACKAGE_PATH "JRamCloud$Object"));
    check_null(cls, "FindClass failed");

    const static jmethodID methodId = env->GetMethodID(cls,
                                          "<init>",
                                          "(L" PACKAGE_PATH "JRamCloud;[B[BJ)V");
    check_null(methodId, "GetMethodID failed");

    return env->NewObject(cls,
                          methodId,
                          jRamCloud,
                          jKey,
                          jValue,
                          static_cast<jlong>(version));
}

/*
 * Class:     edu_stanford_ramcloud_JRamCloud
 * Method:    read
 * Signature: (J[BLJRamCloud/RejectRules;)LJRamCloud/Object;
 */
JNIEXPORT jobject
JNICALL Java_edu_stanford_ramcloud_JRamCloud_read__J_3BLJRamCloud_RejectRules_2(JNIEnv *env,
                                                          jobject jRamCloud,
                                                          jlong jTableId,
                                                          jbyteArray jKey,
                                                          jobject jRejectRules)
{
    // XXX-- implement me by generalising the other read() method.
    return NULL;
}

/*
 * Class:     edu_stanford_ramcloud_JRamCloud
 * Method:    multiRead
 * Signature: ([Ledu/stanford/ramcloud/JRamCloud$multiReadObject;I)[Ledu/stanford/ramcloud/JRamCloud$Object;
 */
JNIEXPORT jobjectArray
JNICALL Java_edu_stanford_ramcloud_JRamCloud_multiRead(JNIEnv *env,   
                                                        jobject jRamCloud,
							jlongArray jTableId,
							jobjectArray jKeyData,
							jshortArray jKeyDataSize,
							jint jrequestNum){

    RamCloud* ramcloud = getRamCloud(env, jRamCloud);
    MultiReadObject objects[jrequestNum];
    Tub<Buffer> values[jrequestNum];
    jbyteArray jKey[jrequestNum];
    MultiReadObject* requests[jrequestNum];

    jlong TableId;
    jshort KeyDataSize;
    jbyte* data[jrequestNum];

    for (int i = 0 ; i < jrequestNum ; i++){
        jKey[i] = (jbyteArray)env->GetObjectArrayElement(jKeyData, i); 

        env->GetShortArrayRegion(jKeyDataSize, i, 1, &KeyDataSize);

        data[i] = (jbyte *) malloc(KeyDataSize);
        env->GetByteArrayRegion(jKey[i], 0, KeyDataSize, data[i]);

        env->GetLongArrayRegion(jTableId, i, 1, &TableId);
        objects[i].tableId = TableId;
        objects[i].key = data[i];
	objects[i].keyLength = KeyDataSize;
        objects[i].value = &values[i];
        requests[i] = &objects[i];
    }

    try {
        ramcloud->multiRead(requests, jrequestNum);
    } EXCEPTION_CATCHER(NULL);
    
    const static jclass jc_RcObject = (jclass)env->NewGlobalRef(env->FindClass(PACKAGE_PATH "JRamCloud$Object"));
    check_null(jc_RcObject, "FindClass failed");
    const static jmethodID jm_init = env->GetMethodID(jc_RcObject,
                                        "<init>",
                                        "(L" PACKAGE_PATH "JRamCloud;[B[BJ)V");

    jobjectArray outJNIArray = env->NewObjectArray(jrequestNum, jc_RcObject , NULL);
    check_null(outJNIArray, "NewObjectArray failed");
    
    for (int i = 0 ; i < jrequestNum ; i++) {
	if (objects[i].status == 0) {
	    jbyteArray jValue = env->NewByteArray(values[i].get()->getTotalLength());
	    check_null(jValue, "NewByteArray failed");
	    JByteArrayGetter value(env, jValue);
	    values[i].get()->copy(0, values[i].get()->getTotalLength(), value.pointer);
	    jobject obj = env->NewObject(jc_RcObject, jm_init, jRamCloud, jKey[i], jValue);
	    check_null(obj, "NewObject failed");
	    env->SetObjectArrayElement(outJNIArray, i, obj);
	}
	free(data[i]);
    }
    return outJNIArray;
}


/*
 * Class:     edu_stanford_ramcloud_JRamCloud
 * Method:    remove
 * Signature: (J[B)J
 */
JNIEXPORT jlong
JNICALL Java_edu_stanford_ramcloud_JRamCloud_remove__J_3B(JNIEnv *env,
                                    jobject jRamCloud,
                                    jlong jTableId,
                                    jbyteArray jKey)
{
    RamCloud* ramcloud = getRamCloud(env, jRamCloud);
    JByteArrayReference key(env, jKey);
    uint64_t version;
    try {
        ramcloud->remove(jTableId, key.pointer, key.length, NULL, &version);
    } EXCEPTION_CATCHER(-1);
    return static_cast<jlong>(version);
}


// Workaround for javah generating incorrect signature for inner class
// 00024 is an escaped signature for $ character
#ifdef __cplusplus
extern "C" {
#endif
JNIEXPORT jlong JNICALL Java_edu_stanford_ramcloud_JRamCloud_remove__J_3BLedu_stanford_ramcloud_JRamCloud_00024RejectRules_2
  (JNIEnv *, jobject, jlong, jbyteArray, jobject);
#ifdef __cplusplus
}
#endif

/*
 * Class:     edu_stanford_ramcloud_JRamCloud
 * Method:    remove
 * Signature: (J[BLedu/stanford/ramcloud/JRamCloud/$RejectRules;)J
 */
JNIEXPORT jlong
JNICALL Java_edu_stanford_ramcloud_JRamCloud_remove__J_3BLedu_stanford_ramcloud_JRamCloud_00024RejectRules_2(JNIEnv *env,
                                                           jobject jRamCloud,
                                                           jlong jTableId,
                                                           jbyteArray jKey,
                                                           jobject jRejectRules)
{
    // XXX- handle RejectRules
    RamCloud* ramcloud = getRamCloud(env, jRamCloud);
    JByteArrayReference key(env, jKey);
    uint64_t version;
    try {
        ramcloud->remove(jTableId, key.pointer, key.length, NULL, &version);
    } EXCEPTION_CATCHER(-1);
    return static_cast<jlong>(version);
}

/*
 * Class:     edu_stanford_ramcloud_JRamCloud
 * Method:    write
 * Signature: (J[B[B)J
 */
JNIEXPORT jlong
JNICALL Java_edu_stanford_ramcloud_JRamCloud_write__J_3B_3B(JNIEnv *env,
                                      jobject jRamCloud,
                                      jlong jTableId,
                                      jbyteArray jKey,
                                      jbyteArray jValue)
{
    RamCloud* ramcloud = getRamCloud(env, jRamCloud);
    JByteArrayReference key(env, jKey);
    JByteArrayGetter value(env, jValue);
    uint64_t version;
    try {
        ramcloud->write(jTableId,
                        key.pointer, key.length,
                        value.pointer, value.length,
                        NULL,
                        &version);
    } EXCEPTION_CATCHER(-1);
    return static_cast<jlong>(version);
}

/*
 * Class:     edu_stanford_ramcloud_JRamCloud
 * Method:    write
 * Signature: (J[B[BLJRamCloud/RejectRules;)J
 */
JNIEXPORT jlong
JNICALL Java_edu_stanford_ramcloud_JRamCloud_write__J_3B_3BLJRamCloud_RejectRules_2(JNIEnv *env,
                                                           jobject jRamCloud,
                                                           jlong jTableId,
                                                           jbyteArray jKey,
                                                           jbyteArray jValue,
                                                           jobject jRejectRules)
{
    // XXX- handle RejectRules    
    RamCloud* ramcloud = getRamCloud(env, jRamCloud);
    JByteArrayReference key(env, jKey);
    JByteArrayGetter value(env, jValue);
    RejectRules rules;
    jclass ruleClass = env->GetObjectClass(jRejectRules);
    jfieldID fid = env->GetFieldID(ruleClass, "doesntExist", "Z");
    rules.doesntExist = (uint8_t) env->GetBooleanField(jRejectRules, fid);

    fid = env->GetFieldID(ruleClass, "exists", "Z");
    rules.exists = (uint8_t) env->GetBooleanField(jRejectRules, fid);

    fid = env->GetFieldID(ruleClass, "givenVersion", "J");
    rules.givenVersion = env->GetLongField(jRejectRules, fid);

    fid = env->GetFieldID(ruleClass, "versionLeGiven", "Z");
    rules.versionLeGiven = (uint8_t) env->GetBooleanField(jRejectRules, fid);

    fid = env->GetFieldID(ruleClass, "versionNeGiven", "Z");
    rules.versionNeGiven = (uint8_t) env->GetBooleanField(jRejectRules, fid);

    uint64_t version;
    try {
        ramcloud->write(jTableId,
                key.pointer, key.length,
                value.pointer, value.length,
                &rules,
                &version);
    }
    EXCEPTION_CATCHER(-1);
    return static_cast<jlong> (version);
}

JNIEXPORT jlong
JNICALL Java_edu_stanford_ramcloud_JRamCloud_writeRule(JNIEnv *env,
        jobject jRamCloud,
        jlong jTableId,
        jbyteArray jKey,
        jbyteArray jValue,
        jobject jRejectRules) {
    RamCloud* ramcloud = getRamCloud(env, jRamCloud);
    JByteArrayReference key(env, jKey);
    JByteArrayGetter value(env, jValue);
    uint64_t version;
    RejectRules rules = {};
    const static jclass jc_RejectRules = (jclass)env->NewGlobalRef(env->FindClass(PACKAGE_PATH "JRamCloud$RejectRules"));

    const static jfieldID jf_doesntExist = env->GetFieldID(jc_RejectRules, "doesntExist", "Z");
    check_null(jf_doesntExist, "doesentExist field id is null");
    jboolean ruleBool;
    ruleBool = env->GetBooleanField(jRejectRules, jf_doesntExist);
    rules.doesntExist = ruleBool ? 1 : 0;

    const static jfieldID jf_exists = env->GetFieldID(jc_RejectRules, "exists", "Z");
    check_null(jf_exists, "exists field id is null");
    ruleBool = env->GetBooleanField(jRejectRules, jf_exists);
    rules.exists = ruleBool ? 1 : 0;

    const static jfieldID jf_givenVersion = env->GetFieldID(jc_RejectRules, "givenVersion", "J");
    check_null(jf_givenVersion, "givenVersion field id is null");
    rules.givenVersion = env->GetLongField(jRejectRules, jf_givenVersion);

    const static jfieldID jf_versionLeGiven = env->GetFieldID(jc_RejectRules, "versionLeGiven", "Z");
    check_null(jf_versionLeGiven, "versionLeGiven field id is null");
    ruleBool = env->GetBooleanField(jRejectRules, jf_versionLeGiven);
    rules.versionLeGiven = ruleBool ? 1 : 0;

    const static jfieldID jf_versionNeGiven = env->GetFieldID(jc_RejectRules, "versionNeGiven", "Z");
    check_null(jf_versionNeGiven, "versionNeGiven field id is null");
    ruleBool = env->GetBooleanField(jRejectRules, jf_versionNeGiven);
    rules.versionNeGiven = ruleBool ? 1 : 0;
    try {
        ramcloud->write(jTableId,
                key.pointer, key.length,
                value.pointer, value.length,
                &rules,
                &version);
    }
    EXCEPTION_CATCHER(-1);
    return static_cast<jlong> (version);
}

/*
 * Class:     edu_stanford_ramcloud_JRamCloud_TableEnumerator
 * Method:    init
 * Signature: (J)V
 */
JNIEXPORT jlong JNICALL Java_edu_stanford_ramcloud_JRamCloud_00024TableEnumerator_init(JNIEnv *env, 
                                                                                      jobject jTableEnumerator, 
                                                                                      jlong jTableId)
{
    const static jclass cls = (jclass)env->NewGlobalRef(env->FindClass(PACKAGE_PATH "JRamCloud$TableEnumerator"));
    const static jfieldID fieldId = env->GetFieldID(cls, "ramCloudObjectPointer", "J");
    RamCloud* ramcloud = reinterpret_cast<RamCloud*>(env->GetLongField(jTableEnumerator, fieldId));
  
    return reinterpret_cast<jlong>(new TableEnumerator(*ramcloud, jTableId));
}

/*
 * Class:     edu_stanford_ramcloud_JRamCloud_TableEnumerator
 * Method:    hasNext
 * Signature: ()Z
 */
JNIEXPORT jboolean JNICALL Java_edu_stanford_ramcloud_JRamCloud_00024TableEnumerator_hasNext( JNIEnv *env, 
                                                                                              jobject jTableEnumerator)
{
    TableEnumerator* tableEnum = getTableEnumerator(env, jTableEnumerator);
    return static_cast<jboolean>(tableEnum->hasNext());
}

/*
 * Class:     edu_stanford_ramcloud_JRamCloud_TableEnumerator
 * Method:    next
 * Signature: ()Ledu/stanford/ramcloud/JRamCloud/Object;
 */
JNIEXPORT jobject JNICALL Java_edu_stanford_ramcloud_JRamCloud_00024TableEnumerator_next( JNIEnv *env, 
                                                                                          jobject jTableEnumerator)
{
    TableEnumerator* tableEnum = getTableEnumerator(env, jTableEnumerator);

    if(tableEnum->hasNext()) 
    {
        uint32_t size = 0;
        const void* buffer = 0;
        uint64_t version = 0;

        tableEnum->next(&size, &buffer);
        Object object(buffer, size);

        jbyteArray jKey = env->NewByteArray(object.getKeyLength());
        jbyteArray jValue = env->NewByteArray(object.getDataLength());
        
        JByteArrayGetter key(env, jKey);
        JByteArrayGetter value(env, jValue);

        memcpy(key.pointer, object.getKey(), object.getKeyLength());
        memcpy(value.pointer, object.getData(), object.getDataLength());

        version = object.getVersion();
        
        const static jclass cls = (jclass)env->NewGlobalRef(env->FindClass(PACKAGE_PATH "JRamCloud$Object"));
        check_null(cls, "FindClass failed");
        const static jmethodID methodId = env->GetMethodID(cls,
                                          "<init>",
                                          "(L" PACKAGE_PATH "JRamCloud;[B[BJ)V");
        check_null(methodId, "GetMethodID failed");
        return env->NewObject(cls,
                              methodId,
                              jTableEnumerator,
                              jKey,
                              jValue,
                              static_cast<jlong>(version));        
    } else 
        return NULL;
}

/*
 * Class:     edu_stanford_ramcloud_JRamCloud
 * Method:    multiWrite
 * Signature: ([Ledu/stanford/ramcloud/JRamCloud/MultiWriteObject;)[Ledu/stanford/ramcloud/JRamCloud/MultiWriteRspObject;
 */
JNIEXPORT jobjectArray JNICALL Java_edu_stanford_ramcloud_JRamCloud_multiWrite(JNIEnv *env, jobject jRamCloud, jobjectArray jmultiWriteArray) {
    jint requestNum = env->GetArrayLength(jmultiWriteArray);
    RamCloud* ramcloud = getRamCloud(env, jRamCloud);
    Tub<MultiWriteObject> objects[requestNum];
    MultiWriteObject *requests[requestNum];
    RejectRules rules[requestNum];
    jbyteArray jKey[requestNum];
    jbyteArray jValue[requestNum];
    
    const static jclass jc_multiWriteObject = (jclass)env->NewGlobalRef(env->FindClass(PACKAGE_PATH "JRamCloud$MultiWriteObject"));
    const static jclass jc_RejectRules = (jclass)env->NewGlobalRef(env->FindClass(PACKAGE_PATH "JRamCloud$RejectRules"));
    const static jfieldID jf_tableId = env->GetFieldID(jc_multiWriteObject, "tableId", "J");
    const static jfieldID jf_key = env->GetFieldID(jc_multiWriteObject, "key", "[B");
    const static jfieldID jf_value = env->GetFieldID(jc_multiWriteObject, "value", "[B");
    const static jfieldID jf_reject_rules = env->GetFieldID(jc_multiWriteObject, "rules", "L" PACKAGE_PATH "JRamCloud$RejectRules;");

    const static jfieldID jf_doesntExist = env->GetFieldID(jc_RejectRules, "doesntExist", "Z");
    check_null(jf_doesntExist, "doesentExist field id is null");
    const static jfieldID jf_exists = env->GetFieldID(jc_RejectRules, "exists", "Z");
    check_null(jf_exists, "exists field id is null");
    const static jfieldID jf_givenVersion = env->GetFieldID(jc_RejectRules, "givenVersion", "J");
    check_null(jf_givenVersion, "givenVersion field id is null");
    const static jfieldID jf_versionLeGiven = env->GetFieldID(jc_RejectRules, "versionLeGiven", "Z");
    check_null(jf_versionLeGiven, "versionLeGiven field id is null");
    const static jfieldID jf_versionNeGiven = env->GetFieldID(jc_RejectRules, "versionNeGiven", "Z");
    check_null(jf_versionNeGiven, "versionNeGiven field id is null");

    for (int i = 0; i < requestNum; i++) {
        jobject obj = env->GetObjectArrayElement(jmultiWriteArray, i);
        check_null(obj, "multi write GetObjectArrayElement failed");

        uint64_t tableId = env->GetLongField(obj, jf_tableId);

        jKey[i] = (jbyteArray)env->GetObjectField(obj, jf_key);
        jbyte* keyData = env->GetByteArrayElements(jKey[i], NULL);
        uint16_t keyLength = env->GetArrayLength(jKey[i]);

        jValue[i] = (jbyteArray)env->GetObjectField(obj, jf_value);
        jbyte* valueData = env->GetByteArrayElements(jValue[i], NULL);
        uint32_t valueLength = env->GetArrayLength(jValue[i]);

        jobject jRejectRules = env->GetObjectField(obj, jf_reject_rules);
        rules[i] = {};

        if (jRejectRules != NULL) {
            jboolean ruleBool;

            ruleBool = env->GetBooleanField(jRejectRules, jf_doesntExist);
            rules[i].doesntExist = ruleBool ? 1 : 0;

            ruleBool = env->GetBooleanField(jRejectRules, jf_exists);
            rules[i].exists = ruleBool ? 1 : 0;

            rules[i].givenVersion = env->GetLongField(jRejectRules, jf_givenVersion);

            ruleBool = env->GetBooleanField(jRejectRules, jf_versionLeGiven);
            rules[i].versionLeGiven = ruleBool ? 1 : 0;

            ruleBool = env->GetBooleanField(jRejectRules, jf_versionNeGiven);
            rules[i].versionNeGiven = ruleBool ? 1 : 0;
        }
        objects[i].construct(tableId, keyData, keyLength, valueData, valueLength, &rules[i]);
        requests[i] = objects[i].get();
    }
    try {
        ramcloud->multiWrite(requests, requestNum);
    } EXCEPTION_CATCHER(NULL);
 
    const static jclass jc_RcObject = (jclass)env->NewGlobalRef(env->FindClass(PACKAGE_PATH "JRamCloud$MultiWriteRspObject"));
    check_null(jc_RcObject, "FindClass failed");
    const static jmethodID jm_init = env->GetMethodID(jc_RcObject,
                                        "<init>",
                                        "(L" PACKAGE_PATH "JRamCloud;IJ)V");

    jobjectArray outJNIArray = env->NewObjectArray(requestNum, jc_RcObject , NULL);
    check_null(outJNIArray, "NewObjectArray failed");
    
    for (int i = 0 ; i < requestNum ; i++) {
        jobject obj = env->NewObject(jc_RcObject, jm_init, jRamCloud, objects[i]->status, objects[i]->version);
        check_null(obj, "NewObject failed");
        env->SetObjectArrayElement(outJNIArray, i, obj);
        env->ReleaseByteArrayElements(jKey[i], (jbyte *)requests[i]->key, JNI_ABORT);
        env->ReleaseByteArrayElements(jValue[i], (jbyte *)requests[i]->value, JNI_ABORT);
        objects[i].destroy();
    }
    return outJNIArray;
}