Memory Leaks in JNI code

Question

Hi,
I have written a small C++ code which will load a JDBC Driver and connect to the database.
The code initially Loads the JVM & than connects to the Database.
When i tested the code with Boundscheket I found a conciderable amount of memory leak & all of these are shown in jvm.dll, zip.dll & java.dll. Is this OK? Are there memory leaks in JNI?

Answer 1

Hi, Please go through the code & let me know if there are any memory leaks in this code. Boundchecker detects a considerable amount of memory leak :(
#include <windows.h>
#include <stdio.h>
#include <jni.h>
#include <conio.h>
#define INI_MAX_PROPERTY_VALUE 1024
#define JVMPATH "C:\\Java\\jdk1.5\\jre\\bin\\client\\jvm.dll"
#define JDBCDRIVER "-Djava.class.path=D:\\mysql-connector-java.jar";
#define CONNECTIONSTRING "jdbc:mysql://localhost:3306/test?user=root&password=root"
#define DRIVERCLASS "com/mysql/jdbc/Driver"
JavaVM *jvm = NULL;
unsigned long int jvmVersion = 0x00010004;
HINSTANCE lib_handle = NULL;
void fini() {
     jint res = jvm->DestroyJavaVM();
     printf ("Destroying JVM %d\n",res);
     if (lib_handle) {
          FreeLibrary(lib_handle);
          printf ("Deleted lib handle\n");
void init()
     char jvmPath[INI_MAX_PROPERTY_VALUE + 1];
     jint res = -1;
     JNIEnv *jniEnv = NULL;
     JavaVMInitArgs vm_args;
     JavaVMOption options[1];
     options[0].optionString = JDBCDRIVER;
     vm_args.version = jvmVersion;
vm_args.options = options;
vm_args.nOptions = 1;
vm_args.ignoreUnrecognized = JNI_TRUE;
     memset(jvmPath, '\0', INI_MAX_PROPERTY_VALUE + 1);
     strcpy(jvmPath,JVMPATH);
     printf("Loading dll from %s\n",jvmPath);
     lib_handle = LoadLibrary(jvmPath);
     if (!lib_handle)
          printf("Error during LoadLibrary\n");
          return;
     printf("JVM dll Loaded Sucessfully\n");
     jint (__stdcall JNI_CreateJavaVM)( JavaVM*, void**, void*);
     JNI_CreateJavaVM = (jint (__stdcall *)(JavaVM**, void**, void*))GetProcAddress(lib_handle, "JNI_CreateJavaVM");
     if (NULL != JNI_CreateJavaVM)
          res = (JNI_CreateJavaVM)( &jvm, (void**)&jniEnv , &vm_args);
     if ( res < 0 ) {
          printf("Unable to create JVM\n");
     } else {
          printf("JVM Created Succesfully\n");
void printException(JNIEnv *jniEnv) {
     jthrowable exceptionHandle = jniEnv->ExceptionOccurred();
     if ( exceptionHandle == NULL )
          return;
     /* Clear the exception from the enviroment*/
     jniEnv->ExceptionClear();
     /* Obtain the JavaException object to get its details */
     jclass jThrowableClass = jniEnv->GetObjectClass(exceptionHandle);
     if ( jThrowableClass == NULL ) {
          if (exceptionHandle)
               jniEnv->DeleteLocalRef(exceptionHandle);     
          exceptionHandle = NULL;
          return ;
     printf("\n*****----- Java Error Message is -----*****\n");
     jmethodID midMessage = jniEnv->GetMethodID( jThrowableClass, "toString", "()Ljava/lang/String;" );
     if ( midMessage == NULL ){
          if (exceptionHandle)
               jniEnv->DeleteLocalRef(exceptionHandle);
          if (jThrowableClass)
               jniEnv->DeleteLocalRef(jThrowableClass);
          exceptionHandle = NULL;
          jThrowableClass = NULL;
          return;
     jstring jstrRet = (jstring)jniEnv->CallObjectMethod(exceptionHandle,midMessage);
     if ( jstrRet == NULL ){
          if (exceptionHandle)
               jniEnv->DeleteLocalRef(exceptionHandle);
          if (jThrowableClass)
               jniEnv->DeleteLocalRef(jThrowableClass);
          exceptionHandle = NULL;
          jThrowableClass = NULL;
          return;
     jboolean flg;
     const char *pExceptionStr = jniEnv->GetStringUTFChars(jstrRet, &flg);
     if ( flg == JNI_TRUE ) {
          printf("%s",pExceptionStr);
          jniEnv->ReleaseStringUTFChars(jstrRet, pExceptionStr);
     if (exceptionHandle)
          jniEnv->DeleteLocalRef(exceptionHandle);
     if (jThrowableClass)
          jniEnv->DeleteLocalRef(jThrowableClass);
     if (jstrRet)
          jniEnv->DeleteLocalRef(jstrRet);
     exceptionHandle = NULL;
     jThrowableClass = NULL;
     jstrRet = NULL;
     printf("\n**************---------End of Java Error Message ************\n");
     return;
void connect() {
     jint res = -1;
     JNIEnv *jniEnv = NULL;
     jclass clsDriver = NULL;
     jmethodID colnstructorDriver = NULL;
     jmethodID methodConnect = NULL;
     jobject objectDriver = NULL;
     jobject objectConnection = NULL;
     jstring jConnectionString = NULL;
     printf("Getting the Enviroment\n");
     jint isPresent = jvm->GetEnv((void **)&jniEnv, jvmVersion );
     if (isPresent == JNI_EDETACHED || jniEnv == NULL) {
          printf("Could not get JNI Env for current thread");
return;
     printf("Creating Instance of Driver\n");
     clsDriver = jniEnv->FindClass(DRIVERCLASS);
     colnstructorDriver = jniEnv->GetMethodID(clsDriver, "<init>", "()V");
     objectDriver = jniEnv->NewObject( clsDriver, colnstructorDriver );
     printf("Created Instance of Driver\n");
     printf("Connecting to the Database\n");
     methodConnect = jniEnv->GetMethodID(clsDriver, "connect", "(Ljava/lang/String;Ljava/util/Properties;)Ljava/sql/Connection;");
     jConnectionString = jniEnv->NewStringUTF(CONNECTIONSTRING);
     objectConnection = jniEnv->CallObjectMethod(objectDriver, methodConnect, jConnectionString, NULL);
     if (objectConnection == NULL) {
          printException(jniEnv);
          printf("Unable to Connect\n");
     else
          printf("Connection Done\n");
     //Releasing all the memory used....
     if (objectConnection)
          jniEnv->DeleteLocalRef(objectConnection);
     if (jConnectionString)
          jniEnv->DeleteLocalRef(jConnectionString);
     if (objectDriver)
          jniEnv->DeleteLocalRef(objectDriver);
     if (clsDriver)
          jniEnv->DeleteLocalRef(clsDriver);
     objectConnection = NULL;
     jConnectionString = NULL;
     objectDriver = NULL;
     clsDriver = NULL;
int main() {
     printf ("Starting...\n");
     init();
     connect();
     fini();
     getch();
}