hadoop/hadoop-hdfs-project/hadoop-hdfs-native-client/src/main/native/libhdfs/jni_helper.c

/**
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#include "config.h"
#include "exception.h"
#include "jni_helper.h"
#include "platform.h"
#include "common/htable.h"
#include "os/mutexes.h"
#include "os/thread_local_storage.h"

#include <errno.h>
#include <dirent.h>
#include <stdio.h> 
#include <string.h> 

static struct htable *gClassRefHTable = NULL;

/** The Native return types that methods could return */
#define JVOID         'V'
#define JOBJECT       'L'
#define JARRAYOBJECT  '['
#define JBOOLEAN      'Z'
#define JBYTE         'B'
#define JCHAR         'C'
#define JSHORT        'S'
#define JINT          'I'
#define JLONG         'J'
#define JFLOAT        'F'
#define JDOUBLE       'D'


/**
 * MAX_HASH_TABLE_ELEM: The maximum no. of entries in the hashtable.
 * It's set to 4096 to account for (classNames + No. of threads)
 */
#define MAX_HASH_TABLE_ELEM 4096

/**
 * Length of buffer for retrieving created JVMs.  (We only ever create one.)
 */
#define VM_BUF_LENGTH 1

void destroyLocalReference(JNIEnv *env, jobject jObject)
{
  if (jObject)
    (*env)->DeleteLocalRef(env, jObject);
}

static jthrowable validateMethodType(JNIEnv *env, MethType methType)
{
    if (methType != STATIC && methType != INSTANCE) {
        return newRuntimeError(env, "validateMethodType(methType=%d): "
            "illegal method type.\n", methType);
    }
    return NULL;
}

jthrowable newJavaStr(JNIEnv *env, const char *str, jstring *out)
{
    jstring jstr;

    if (!str) {
        /* Can't pass NULL to NewStringUTF: the result would be
         * implementation-defined. */
        *out = NULL;
        return NULL;
    }
    jstr = (*env)->NewStringUTF(env, str);
    if (!jstr) {
        /* If NewStringUTF returns NULL, an exception has been thrown,
         * which we need to handle.  Probaly an OOM. */
        return getPendingExceptionAndClear(env);
    }
    *out = jstr;
    return NULL;
}

jthrowable newCStr(JNIEnv *env, jstring jstr, char **out)
{
    const char *tmp;

    if (!jstr) {
        *out = NULL;
        return NULL;
    }
    tmp = (*env)->GetStringUTFChars(env, jstr, NULL);
    if (!tmp) {
        return getPendingExceptionAndClear(env);
    }
    *out = strdup(tmp);
    (*env)->ReleaseStringUTFChars(env, jstr, tmp);
    return NULL;
}

jthrowable invokeMethod(JNIEnv *env, jvalue *retval, MethType methType,
                 jobject instObj, const char *className,
                 const char *methName, const char *methSignature, ...)
{
    va_list args;
    jclass cls;
    jmethodID mid;
    jthrowable jthr;
    const char *str; 
    char returnType;
    
    jthr = validateMethodType(env, methType);
    if (jthr)
        return jthr;
    jthr = globalClassReference(className, env, &cls);
    if (jthr)
        return jthr;
    jthr = methodIdFromClass(className, methName, methSignature, 
                            methType, env, &mid);
    if (jthr)
        return jthr;
    str = methSignature;
    while (*str != ')') str++;
    str++;
    returnType = *str;
    va_start(args, methSignature);
    if (returnType == JOBJECT || returnType == JARRAYOBJECT) {
        jobject jobj = NULL;
        if (methType == STATIC) {
            jobj = (*env)->CallStaticObjectMethodV(env, cls, mid, args);
        }
        else if (methType == INSTANCE) {
            jobj = (*env)->CallObjectMethodV(env, instObj, mid, args);
        }
        retval->l = jobj;
    }
    else if (returnType == JVOID) {
        if (methType == STATIC) {
            (*env)->CallStaticVoidMethodV(env, cls, mid, args);
        }
        else if (methType == INSTANCE) {
            (*env)->CallVoidMethodV(env, instObj, mid, args);
        }
    }
    else if (returnType == JBOOLEAN) {
        jboolean jbool = 0;
        if (methType == STATIC) {
            jbool = (*env)->CallStaticBooleanMethodV(env, cls, mid, args);
        }
        else if (methType == INSTANCE) {
            jbool = (*env)->CallBooleanMethodV(env, instObj, mid, args);
        }
        retval->z = jbool;
    }
    else if (returnType == JSHORT) {
        jshort js = 0;
        if (methType == STATIC) {
            js = (*env)->CallStaticShortMethodV(env, cls, mid, args);
        }
        else if (methType == INSTANCE) {
            js = (*env)->CallShortMethodV(env, instObj, mid, args);
        }
        retval->s = js;
    }
    else if (returnType == JLONG) {
        jlong jl = -1;
        if (methType == STATIC) {
            jl = (*env)->CallStaticLongMethodV(env, cls, mid, args);
        }
        else if (methType == INSTANCE) {
            jl = (*env)->CallLongMethodV(env, instObj, mid, args);
        }
        retval->j = jl;
    }
    else if (returnType == JINT) {
        jint ji = -1;
        if (methType == STATIC) {
            ji = (*env)->CallStaticIntMethodV(env, cls, mid, args);
        }
        else if (methType == INSTANCE) {
            ji = (*env)->CallIntMethodV(env, instObj, mid, args);
        }
        retval->i = ji;
    }
    va_end(args);

    jthr = (*env)->ExceptionOccurred(env);
    if (jthr) {
        (*env)->ExceptionClear(env);
        return jthr;
    }
    return NULL;
}

jthrowable constructNewObjectOfClass(JNIEnv *env, jobject *out, const char *className, 
                                  const char *ctorSignature, ...)
{
    va_list args;
    jclass cls;
    jmethodID mid; 
    jobject jobj;
    jthrowable jthr;

    jthr = globalClassReference(className, env, &cls);
    if (jthr)
        return jthr;
    jthr = methodIdFromClass(className, "<init>", ctorSignature, 
                            INSTANCE, env, &mid);
    if (jthr)
        return jthr;
    va_start(args, ctorSignature);
    jobj = (*env)->NewObjectV(env, cls, mid, args);
    va_end(args);
    if (!jobj)
        return getPendingExceptionAndClear(env);
    *out = jobj;
    return NULL;
}


jthrowable methodIdFromClass(const char *className, const char *methName, 
                            const char *methSignature, MethType methType, 
                            JNIEnv *env, jmethodID *out)
{
    jclass cls;
    jthrowable jthr;
    jmethodID mid = 0;

    jthr = globalClassReference(className, env, &cls);
    if (jthr)
        return jthr;
    jthr = validateMethodType(env, methType);
    if (jthr)
        return jthr;
    if (methType == STATIC) {
        mid = (*env)->GetStaticMethodID(env, cls, methName, methSignature);
    }
    else if (methType == INSTANCE) {
        mid = (*env)->GetMethodID(env, cls, methName, methSignature);
    }
    if (mid == NULL) {
        fprintf(stderr, "could not find method %s from class %s with "
            "signature %s\n", methName, className, methSignature);
        return getPendingExceptionAndClear(env);
    }
    *out = mid;
    return NULL;
}

jthrowable globalClassReference(const char *className, JNIEnv *env, jclass *out)
{
    jthrowable jthr = NULL;
    jclass local_clazz = NULL;
    jclass clazz = NULL;
    int ret;

    mutexLock(&hdfsHashMutex);
    if (!gClassRefHTable) {
        gClassRefHTable = htable_alloc(MAX_HASH_TABLE_ELEM, ht_hash_string,
            ht_compare_string);
        if (!gClassRefHTable) {
            jthr = newRuntimeError(env, "htable_alloc failed\n");
            goto done;
        }
    }
    clazz = htable_get(gClassRefHTable, className);
    if (clazz) {
        *out = clazz;
        goto done;
    }
    local_clazz = (*env)->FindClass(env,className);
    if (!local_clazz) {
        jthr = getPendingExceptionAndClear(env);
        goto done;
    }
    clazz = (*env)->NewGlobalRef(env, local_clazz);
    if (!clazz) {
        jthr = getPendingExceptionAndClear(env);
        goto done;
    }
    ret = htable_put(gClassRefHTable, (void*)className, clazz);
    if (ret) {
        jthr = newRuntimeError(env, "htable_put failed with error "
                               "code %d\n", ret);
        goto done;
    }
    *out = clazz;
    jthr = NULL;
done:
    mutexUnlock(&hdfsHashMutex);
    (*env)->DeleteLocalRef(env, local_clazz);
    if (jthr && clazz) {
        (*env)->DeleteGlobalRef(env, clazz);
    }
    return jthr;
}

jthrowable classNameOfObject(jobject jobj, JNIEnv *env, char **name)
{
    jthrowable jthr;
    jclass cls, clsClass = NULL;
    jmethodID mid;
    jstring str = NULL;
    const char *cstr = NULL;
    char *newstr;

    cls = (*env)->GetObjectClass(env, jobj);
    if (cls == NULL) {
        jthr = getPendingExceptionAndClear(env);
        goto done;
    }
    clsClass = (*env)->FindClass(env, "java/lang/Class");
    if (clsClass == NULL) {
        jthr = getPendingExceptionAndClear(env);
        goto done;
    }
    mid = (*env)->GetMethodID(env, clsClass, "getName", "()Ljava/lang/String;");
    if (mid == NULL) {
        jthr = getPendingExceptionAndClear(env);
        goto done;
    }
    str = (*env)->CallObjectMethod(env, cls, mid);
    if (str == NULL) {
        jthr = getPendingExceptionAndClear(env);
        goto done;
    }
    cstr = (*env)->GetStringUTFChars(env, str, NULL);
    if (!cstr) {
        jthr = getPendingExceptionAndClear(env);
        goto done;
    }
    newstr = strdup(cstr);
    if (newstr == NULL) {
        jthr = newRuntimeError(env, "classNameOfObject: out of memory");
        goto done;
    }
    *name = newstr;
    jthr = NULL;

done:
    destroyLocalReference(env, cls);
    destroyLocalReference(env, clsClass);
    if (str) {
        if (cstr)
            (*env)->ReleaseStringUTFChars(env, str, cstr);
        (*env)->DeleteLocalRef(env, str);
    }
    return jthr;
}


/**
 * For the given path, expand it by filling in with all *.jar or *.JAR files,
 * separated by PATH_SEPARATOR. Assumes that expanded is big enough to hold the
 * string, eg allocated after using this function with expanded=NULL to get the
 * right size. Also assumes that the path ends with a "/.". The length of the
 * expanded path is returned, which includes space at the end for either a
 * PATH_SEPARATOR or null terminator.
 */
static ssize_t wildcard_expandPath(const char* path, char* expanded)
{
    struct dirent* file;
    char* dest = expanded;
    ssize_t length = 0;
    size_t pathLength = strlen(path);
    DIR* dir;

    dir = opendir(path);
    if (dir != NULL) {
        // can open dir so try to match with all *.jar and *.JAR entries

#ifdef _LIBHDFS_JNI_HELPER_DEBUGGING_ON_
        printf("wildcard_expandPath: %s\n", path);
#endif

        errno = 0;
        while ((file = readdir(dir)) != NULL) {
            const char* filename = file->d_name;
            const size_t filenameLength = strlen(filename);
            const char* jarExtension;

            // If filename is smaller than 4 characters then it can not possibly
            // have extension ".jar" or ".JAR"
            if (filenameLength < 4) {
                continue;
            }

            jarExtension = &filename[filenameLength-4];
            if ((strcmp(jarExtension, ".jar") == 0) ||
                (strcmp(jarExtension, ".JAR") == 0)) {

                // pathLength includes an extra '.' which we'll use for either
                // separator or null termination
                length += pathLength + filenameLength;

#ifdef _LIBHDFS_JNI_HELPER_DEBUGGING_ON_
                printf("wildcard_scanPath:\t%s\t:\t%zd\n", filename, length);
#endif

                if (expanded != NULL) {
                    // pathLength includes an extra '.'
                    strncpy(dest, path, pathLength-1);
                    dest += pathLength - 1;
                    strncpy(dest, filename, filenameLength);
                    dest += filenameLength;
                    *dest = PATH_SEPARATOR;
                    dest++;

#ifdef _LIBHDFS_JNI_HELPER_DEBUGGING_ON_
                    printf("wildcard_expandPath:\t%s\t:\t%s\n",
                      filename, expanded);
#endif
                }
            }
        }

        if (errno != 0) {
            fprintf(stderr, "wildcard_expandPath: on readdir %s: %s\n",
              path, strerror(errno));
            length = -1;
        }

        if (closedir(dir) != 0) {
            fprintf(stderr, "wildcard_expandPath: on closedir %s: %s\n",
                    path, strerror(errno));
        }
    } else if ((errno != EACCES) && (errno != ENOENT) && (errno != ENOTDIR)) {
        // can not opendir due to an error we can not handle
        fprintf(stderr, "wildcard_expandPath: on opendir %s: %s\n", path,
                strerror(errno));
        length = -1;
    }

    if (length == 0) {
        // either we failed to open dir due to EACCESS, ENOENT, or ENOTDIR, or
        // we did not find any file that matches *.jar or *.JAR

#ifdef _LIBHDFS_JNI_HELPER_DEBUGGING_ON_
        fprintf(stderr, "wildcard_expandPath: can not expand %.*s*: %s\n",
                (int)(pathLength-1), path, strerror(errno));
#endif

        // in this case, the wildcard expansion is the same as the original
        // +1 for PATH_SEPARTOR or null termination
        length = pathLength + 1;
        if (expanded != NULL) {
            // pathLength includes an extra '.'
            strncpy(dest, path, pathLength-1);
            dest += pathLength-1;
            *dest = '*'; // restore wildcard
            dest++;
            *dest = PATH_SEPARATOR;
            dest++;
        }
    }

    return length;
}

/**
 * Helper to expand classpaths. Returns the total length of the expanded
 * classpath. If expandedClasspath is not NULL, then fills that with the
 * expanded classpath. It assumes that expandedClasspath is of correct size, eg
 * allocated after using this function with expandedClasspath=NULL to get the
 * right size.
 */
static ssize_t getClassPath_helper(const char *classpath, char* expandedClasspath)
{
    ssize_t length;
    ssize_t retval;
    char* expandedCP_curr;
    char* cp_token;
    char* classpath_dup;

    classpath_dup = strdup(classpath);
    if (classpath_dup == NULL) {
        fprintf(stderr, "getClassPath_helper: failed strdup: %s\n",
          strerror(errno));
        return -1;
    }

    length = 0;

    // expandedCP_curr is the current pointer
    expandedCP_curr = expandedClasspath;

    cp_token = strtok(classpath_dup, PATH_SEPARATOR_STR);
    while (cp_token != NULL) {
        size_t tokenlen;

#ifdef _LIBHDFS_JNI_HELPER_DEBUGGING_ON_
        printf("%s\n", cp_token);
#endif

        tokenlen = strlen(cp_token);
        // We only expand if token ends with "/*"
        if ((tokenlen > 1) &&
          (cp_token[tokenlen-1] == '*') && (cp_token[tokenlen-2] == '/')) {
            // replace the '*' with '.' so that we don't have to allocate another
            // string for passing to opendir() in wildcard_expandPath()
            cp_token[tokenlen-1] = '.';
            retval = wildcard_expandPath(cp_token, expandedCP_curr);
            if (retval < 0) {
                free(classpath_dup);
                return -1;
            }

            length += retval;
            if (expandedCP_curr != NULL) {
                expandedCP_curr += retval;
            }
        } else {
            // +1 for path separator or null terminator
            length += tokenlen + 1;
            if (expandedCP_curr != NULL) {
                strncpy(expandedCP_curr, cp_token, tokenlen);
                expandedCP_curr += tokenlen;
                *expandedCP_curr = PATH_SEPARATOR;
                expandedCP_curr++;
            }
        }

        cp_token = strtok(NULL, PATH_SEPARATOR_STR);
    }

    // Fix the last ':' and use it to null terminate
    if (expandedCP_curr != NULL) {
        expandedCP_curr--;
        *expandedCP_curr = '\0';
    }

    free(classpath_dup);
    return length;
}

/**
 * Gets the classpath. Wild card entries are resolved only if the entry ends
 * with "/\*" (backslash to escape commenting) to match against .jar and .JAR.
 * All other wild card entries (eg /path/to/dir/\*foo*) are not resolved,
 * following JAVA default behavior, see:
 * https://docs.oracle.com/javase/8/docs/technotes/tools/unix/classpath.html
 */
static char* getClassPath()
{
    char* classpath;
    char* expandedClasspath;
    ssize_t length;
    ssize_t retval;

    classpath = getenv("CLASSPATH");
    if (classpath == NULL) {
      return NULL;
    }

    // First, get the total size of the string we will need for the expanded
    // classpath
    length = getClassPath_helper(classpath, NULL);
    if (length < 0) {
      return NULL;
    }

#ifdef _LIBHDFS_JNI_HELPER_DEBUGGING_ON_
    printf("+++++++++++++++++\n");
#endif

    // we don't have to do anything if classpath has no valid wildcards
    // we get length = 0 when CLASSPATH is set but empty
    // if CLASSPATH is not empty, then length includes null terminator
    // if length of expansion is same as original, then return a duplicate of
    // original since expansion can only be longer
    if ((length == 0) || ((length - 1) == strlen(classpath))) {

#ifdef _LIBHDFS_JNI_HELPER_DEBUGGING_ON_
        if ((length == 0) && (strlen(classpath) != 0)) {
            fprintf(stderr, "Something went wrong with getting the wildcard \
              expansion length\n" );
        }
#endif

        expandedClasspath = strdup(classpath);

#ifdef _LIBHDFS_JNI_HELPER_DEBUGGING_ON_
        printf("Expanded classpath=%s\n", expandedClasspath);
#endif

        return expandedClasspath;
    }

    // Allocte memory for expanded classpath string
    expandedClasspath = calloc(length, sizeof(char));
    if (expandedClasspath == NULL) {
        fprintf(stderr, "getClassPath: failed calloc: %s\n", strerror(errno));
        return NULL;
    }

    // Actual expansion
    retval = getClassPath_helper(classpath, expandedClasspath);
    if (retval < 0) {
        free(expandedClasspath);
        return NULL;
    }

    // This should not happen, but dotting i's and crossing t's
    if (retval != length) {
        fprintf(stderr,
          "Expected classpath expansion length to be %zu but instead got %zu\n",
          length, retval);
        free(expandedClasspath);
        return NULL;
    }

#ifdef _LIBHDFS_JNI_HELPER_DEBUGGING_ON_
    printf("===============\n");
    printf("Allocated %zd for expanding classpath\n", length);
    printf("Used %zu for expanding classpath\n", strlen(expandedClasspath) + 1);
    printf("Expanded classpath=%s\n", expandedClasspath);
#endif

    return expandedClasspath;
}


/**
 * Get the global JNI environemnt.
 *
 * We only have to create the JVM once.  After that, we can use it in
 * every thread.  You must be holding the jvmMutex when you call this
 * function.
 *
 * @return          The JNIEnv on success; error code otherwise
 */
static JNIEnv* getGlobalJNIEnv(void)
{
    JavaVM* vmBuf[VM_BUF_LENGTH]; 
    JNIEnv *env;
    jint rv = 0; 
    jint noVMs = 0;
    jthrowable jthr;
    char *hadoopClassPath;
    const char *hadoopClassPathVMArg = "-Djava.class.path=";
    size_t optHadoopClassPathLen;
    char *optHadoopClassPath;
    int noArgs = 1;
    char *hadoopJvmArgs;
    char jvmArgDelims[] = " ";
    char *str, *token, *savePtr;
    JavaVMInitArgs vm_args;
    JavaVM *vm;
    JavaVMOption *options;

    rv = JNI_GetCreatedJavaVMs(&(vmBuf[0]), VM_BUF_LENGTH, &noVMs);
    if (rv != 0) {
        fprintf(stderr, "JNI_GetCreatedJavaVMs failed with error: %d\n", rv);
        return NULL;
    }

    if (noVMs == 0) {
        //Get the environment variables for initializing the JVM
        hadoopClassPath = getClassPath();
        if (hadoopClassPath == NULL) {
            fprintf(stderr, "Environment variable CLASSPATH not set!\n");
            return NULL;
        } 
        optHadoopClassPathLen = strlen(hadoopClassPath) + 
          strlen(hadoopClassPathVMArg) + 1;
        optHadoopClassPath = malloc(sizeof(char)*optHadoopClassPathLen);
        snprintf(optHadoopClassPath, optHadoopClassPathLen,
                "%s%s", hadoopClassPathVMArg, hadoopClassPath);

        free(hadoopClassPath);

        // Determine the # of LIBHDFS_OPTS args
        hadoopJvmArgs = getenv("LIBHDFS_OPTS");
        if (hadoopJvmArgs != NULL)  {
          hadoopJvmArgs = strdup(hadoopJvmArgs);
          for (noArgs = 1, str = hadoopJvmArgs; ; noArgs++, str = NULL) {
            token = strtok_r(str, jvmArgDelims, &savePtr);
            if (NULL == token) {
              break;
            }
          }
          free(hadoopJvmArgs);
        }

        // Now that we know the # args, populate the options array
        options = calloc(noArgs, sizeof(JavaVMOption));
        if (!options) {
          fputs("Call to calloc failed\n", stderr);
          free(optHadoopClassPath);
          return NULL;
        }
        options[0].optionString = optHadoopClassPath;
        hadoopJvmArgs = getenv("LIBHDFS_OPTS");
	if (hadoopJvmArgs != NULL)  {
          hadoopJvmArgs = strdup(hadoopJvmArgs);
          for (noArgs = 1, str = hadoopJvmArgs; ; noArgs++, str = NULL) {
            token = strtok_r(str, jvmArgDelims, &savePtr);
            if (NULL == token) {
              break;
            }
            options[noArgs].optionString = token;
          }
        }

        //Create the VM
        vm_args.version = JNI_VERSION_1_2;
        vm_args.options = options;
        vm_args.nOptions = noArgs; 
        vm_args.ignoreUnrecognized = 1;

        rv = JNI_CreateJavaVM(&vm, (void*)&env, &vm_args);

        if (hadoopJvmArgs != NULL)  {
          free(hadoopJvmArgs);
        }
        free(optHadoopClassPath);
        free(options);

        if (rv != 0) {
            fprintf(stderr, "Call to JNI_CreateJavaVM failed "
                    "with error: %d\n", rv);
            return NULL;
        }
        jthr = invokeMethod(env, NULL, STATIC, NULL,
                         "org/apache/hadoop/fs/FileSystem",
                         "loadFileSystems", "()V");
        if (jthr) {
            printExceptionAndFree(env, jthr, PRINT_EXC_ALL, "loadFileSystems");
        }
    }
    else {
        //Attach this thread to the VM
        vm = vmBuf[0];
        rv = (*vm)->AttachCurrentThread(vm, (void*)&env, 0);
        if (rv != 0) {
            fprintf(stderr, "Call to AttachCurrentThread "
                    "failed with error: %d\n", rv);
            return NULL;
        }
    }

    return env;
}

/**
 * getJNIEnv: A helper function to get the JNIEnv* for the given thread.
 * If no JVM exists, then one will be created. JVM command line arguments
 * are obtained from the LIBHDFS_OPTS environment variable.
 *
 * Implementation note: we rely on POSIX thread-local storage (tls).
 * This allows us to associate a destructor function with each thread, that
 * will detach the thread from the Java VM when the thread terminates.  If we
 * failt to do this, it will cause a memory leak.
 *
 * However, POSIX TLS is not the most efficient way to do things.  It requires a
 * key to be initialized before it can be used.  Since we don't know if this key
 * is initialized at the start of this function, we have to lock a mutex first
 * and check.  Luckily, most operating systems support the more efficient
 * __thread construct, which is initialized by the linker.
 *
 * @param: None.
 * @return The JNIEnv* corresponding to the thread.
 */
JNIEnv* getJNIEnv(void)
{
    JNIEnv *env;
    THREAD_LOCAL_STORAGE_GET_QUICK();
    mutexLock(&jvmMutex);
    if (threadLocalStorageGet(&env)) {
      mutexUnlock(&jvmMutex);
      return NULL;
    }
    if (env) {
      mutexUnlock(&jvmMutex);
      return env;
    }

    env = getGlobalJNIEnv();
    mutexUnlock(&jvmMutex);
    if (!env) {
      fprintf(stderr, "getJNIEnv: getGlobalJNIEnv failed\n");
      return NULL;
    }
    if (threadLocalStorageSet(env)) {
      return NULL;
    }
    THREAD_LOCAL_STORAGE_SET_QUICK(env);
    return env;
}

int javaObjectIsOfClass(JNIEnv *env, jobject obj, const char *name)
{
    jclass clazz;
    int ret;

    clazz = (*env)->FindClass(env, name);
    if (!clazz) {
        printPendingExceptionAndFree(env, PRINT_EXC_ALL,
            "javaObjectIsOfClass(%s)", name);
        return -1;
    }
    ret = (*env)->IsInstanceOf(env, obj, clazz);
    (*env)->DeleteLocalRef(env, clazz);
    return ret == JNI_TRUE ? 1 : 0;
}

jthrowable hadoopConfSetStr(JNIEnv *env, jobject jConfiguration,
        const char *key, const char *value)
{
    jthrowable jthr;
    jstring jkey = NULL, jvalue = NULL;

    jthr = newJavaStr(env, key, &jkey);
    if (jthr)
        goto done;
    jthr = newJavaStr(env, value, &jvalue);
    if (jthr)
        goto done;
    jthr = invokeMethod(env, NULL, INSTANCE, jConfiguration,
            "org/apache/hadoop/conf/Configuration", "set", 
            "(Ljava/lang/String;Ljava/lang/String;)V",
            jkey, jvalue);
    if (jthr)
        goto done;
done:
    (*env)->DeleteLocalRef(env, jkey);
    (*env)->DeleteLocalRef(env, jvalue);
    return jthr;
}

jthrowable fetchEnumInstance(JNIEnv *env, const char *className,
                         const char *valueName, jobject *out)
{
    jclass clazz;
    jfieldID fieldId;
    jobject jEnum;
    char prettyClass[256];

    clazz = (*env)->FindClass(env, className);
    if (!clazz) {
        return newRuntimeError(env, "fetchEnum(%s, %s): failed to find class.",
                className, valueName);
    }
    if (snprintf(prettyClass, sizeof(prettyClass), "L%s;", className)
          >= sizeof(prettyClass)) {
        return newRuntimeError(env, "fetchEnum(%s, %s): class name too long.",
                className, valueName);
    }
    fieldId = (*env)->GetStaticFieldID(env, clazz, valueName, prettyClass);
    if (!fieldId) {
        return getPendingExceptionAndClear(env);
    }
    jEnum = (*env)->GetStaticObjectField(env, clazz, fieldId);
    if (!jEnum) {
        return getPendingExceptionAndClear(env);
    }
    *out = jEnum;
    return NULL;
}