Anyone can prove JNI is safe? My application crashes after many calls.

Question

I heard that JNI is not safe. In fact I made an application base on many JNI calls.
C level is API supplied by IBM. And I was told the C API is tested and safe.
Java application and JNI calls is writen by myself. It crashed after about 3000 times call. I tried other JDK and other OS. On some platform, the thread hold there after many calls. No error, no crash. But others crashed even early.
Here's my JNI call's code:
JNIEXPORT void JNICALL Java_com_ibm_mm_sdk_cim_internal_PServiceFACImp_cEvaluate
(JNIEnv *env, jclass jobj, jlong jhandle, jstring jmanualedListFilename, jstring jclassedListFileName, jstring jresultFilename){
     char *manualedListFilename = jstringToWindows(env, jmanualedListFilename);
     char *classedListFileName = jstringToWindows(env, jclassedListFileName);
     char *resultFilename = jstringToWindows(env, jresultFilename);
     int rc;                         // API return code
     void* handle;               // FAC Handle
     // convert C pointer from java long type
     handle = (void*)jhandle;
     rc = KmFAC_Evaluate(
          handle,                                   // FAC Handle
          (char*)manualedListFilename,     // File name of list of files
          (char*)classedListFileName,          // File name of list of files
          (char*)resultFilename               // Result file
     if (manualedListFilename)
          free(manualedListFilename);
     if (classedListFileName)
          free(classedListFileName);
     if (resultFilename)
          free(resultFilename);
     if (rc != KM_RC_OK) {
          //Throw exception
          jclass exceptClass;          // JNI exception class
          char errorMsg[256];          // Used to build error msg for exceptions
          jmethodID methodid;          // Exception constructor method id
          sprintf(errorMsg, "KmFAC_Evaluate() [CKM=%d]", (int)rc);
          exceptClass = env->FindClass("com/ibm/mm/sdk/cim/DKServiceExceptionCIM");
          methodid = env->GetMethodID(exceptClass,"<init>","(Ljava/lang/String;II)V");
          jstring str = env->NewStringUTF(errorMsg);
          jthrowable excobj = (jthrowable)env->NewObject(exceptClass,methodid,str,100, (int)rc);
          env->Throw(excobj);
     return;

Answer 1

I agree with fury88. Try the code below it works fine!
// **************** Java portion ************************
public class Test {
// Load the dll that exports functions callable from java
static {System.loadLibrary("TestImp");}
// Imported function declarations
public native void print(String msg);
public void Test() {
public static void main(String [] args) {
Test t = new Test();
// Printf example
     t.print("->Testing JNI - Hello from c++\n");
// **************** Windows portion - TestImp.dll **********************
// Exported function
JNIEXPORT void JNICALL Java_Test_print(JNIEnv *env, jobject obj, jstring msg)
const char *str = env->GetStringUTFChars(msg, 0);
printf("%s\n", str);
env->ReleaseStringUTFChars(msg, str);
// Entry point
BOOL APIENTRY DllMain(HANDLE hModule, DWORD ul_reason_for_call, LPVOID lpReserved)
     switch(ul_reason_for_call)
          case DLL_PROCESS_ATTACH:
               return TRUE;
          case DLL_PROCESS_DETACH:
               return TRUE;
return TRUE;
}