JNI - How to use the error reporting mechanism?

Question

I've developed a C++ DLL which is loaded from a commercial Win32 application (not written by me) as a plug-in for external calculations. On its initialization the C++ DLL launches the Java VM via the JNI invocation interface. When the DLL functions are called by the application, they forward the calls to Java objects inside the Java VM, again via JNI invocation interface.
This works well, but I have encountered a weird error.
From Java I open a JFrame containing a JTextArea as small console for debug output messages. If I turn output to this debug console off (my printToConsole routine checks whether a boolean flag is set), the string concatenation operator may lead to a crash of the Java VM.
For example, if in one of the Java functions called from the
DLL via JNI invocation interface the following is the first statement,
it leads to a crash of the Java VM and the application that loaded the C++ proxy DLL.
String test=""+Math.random(); // String test not used later
Interestingly, if I comment this statement out, the Java code works fine WITHOUT any crash. I've already thought about potential races and synchronization issues in my code, but I don't see where this is the case. And the string concatenation error fails as well, if I insert sleep() statements in front of it and at other places in the code. However, if I turn on log messages printed to my JFrame debug console (containing a JTextArea), the String concatenation works without problems.
So maybe the JNI interface has a bug and affects the Java VM; I don't see where my JNI code is wrong.
One problem is that I do not get any stdout output, as the C++ proxy DLL is loaded by the Windows application, even if I start the Windows application from the DOS command line (under Windows).
Does anyone know how to use the error reporting mechanism?
http://java.sun.com/j2se/1.4.2/docs/guide/vm/error-handling.html
Is it possible that the JVM, when it crashes, writes debug information about the crash into a file instead of stdout/stderr?
My C++ proxy DLL was compiled in debug mode, but the commercial application (which loaded the DLL) is very likely not.
I do not know hot to find the reason why the String concatenation fails inside the Java function called from the C++ DLL via JNI.

Answer 1

Yes, I've initially thought about errors in the C++ code too. But the C++ code is actually very simple and short. It doesn't allocate anything on the C++ side. It allocates a couple of ByteBuffers inside the Java VM however via JNI invocation interface calls of env->NewDirectByteBuffer(). The native memory regions accessed via the ByteBuffers are allocated not by my own C++ code, but by the program that calls my DLL (the program is Metastock).
The interesting thing is that everything works fine if output to my debug console is enabled, which means that in the Java print routine getConsoleLoggingState() returns true and text is appended to the jTextArea.
static synchronized void print(String str)
{ MetaStockMonitor mMon=getInstance();
if ( mMon.getFileLoggingState() && mMon.logFileWriter!=null) {
mMon.logFileWriter.print(str);
mMon.logFileWriter.flush();
if ( mMon.getConsoleLoggingState() ) {
mMon.jTextArea1.append(str);
Only if output to the JTextArea is turned off (ie. getConsoleLoggingState()==false), the crash happens when the FIRST statement in the Java routine called via JNI invocation interface is a (useless) String concatenation operation, as described above.
String test=""+Math.random(); // String test not used later
Moreover, the crash happens BEFORE the allocated ByteBuffer objects are accessed in the Java code. But again, if console output is turned on, it works stable. If console output is turned off, it works when the (useless) String concatenation operation is removed in the Java routine called from C++.
I've already thought about potential races (regarding multiple threads), but this can be ruled out in my case. It almost appears as if the JVM can have problems when called by the invocation interface (I tested it with Java 1.4.2 b28).
All the calls between C++ and Java go ALWAYS in the direction from C++ code to Java. Unfortunately, there is no special JRE version with extensive logging capabilities to facilitate debugging. And the problem is not easily reproducible either.
JNIEnv* JNI_GetEnv()
JNIEnv *env;
cached_jvm->AttachCurrentThread((void**)&env,NULL);
fprintf(logfile,"env=%i\n",env);
fflush(logfile);
return env;
// function called by Metastock's MSX plug-in interface
BOOL __stdcall createIndEngine (const MSXDataRec *a_psDataRec,
const MSXDataInfoRecArgsArray *a_psDataInfoArgs,
const MSXNumericArgsArray *a_psNumericArgs,
const MSXStringArgsArray *a_psStringArgs,
const MSXCustomArgsArray *a_psCustomArgs,
MSXResultRec *a_psResultRec)
a_psResultRec->psResultArray->iFirstValid=0;
a_psResultRec->psResultArray->iLastValid=-1;
jthrowable ex;
jmethodID mid;
JNIEnv* env=JNI_GetEnv();
jobject chart=getChart(env, a_psDataRec);
if ( chart==NULL) {
return MSX_ERROR;
jobject getChart (JNIEnv* env, const MSXDataRec *a_psDataRec)
jthrowable ex;
jmethodID mid;
int closeFirstValid, closeLastValid;
closeFirstValid=a_psDataRec->sClose.iFirstValid;
closeLastValid=a_psDataRec->sClose.iLastValid;
long firstDate, firstTime;
if (closeFirstValid>=1 && closeFirstValid<=closeLastValid) {
firstDate = a_psDataRec->psDate[closeFirstValid].lDate;
firstTime = a_psDataRec->psDate[closeFirstValid].lTime;
} else {
firstDate=0;
firstTime=0;
jclass chartFactoryClass = env->FindClass("wschwendt/metastock/msx/ChartFactory");
if (ex= env->ExceptionOccurred() ) {
env->ExceptionDescribe();
env->ExceptionClear();
sprintf(sbuf, "DLL: Cannot find class ChartFactory\n");
printSBufViaJava(sbuf);
return NULL;
mid = env->GetStaticMethodID(chartFactoryClass, "getInstance", "()Lwschwendt/metastock/msx/ChartFactory;");
if (ex= env->ExceptionOccurred() ) {
env->ExceptionDescribe();
env->ExceptionClear();
sprintf(sbuf, "DLL: Cannot find method ID for ChartFactory.getInstance()\n");
printSBufViaJava(sbuf);
return NULL;
jobject chartFactory=env->CallStaticObjectMethod(chartFactoryClass, mid);
if (ex= env->ExceptionOccurred() ) {
env->ExceptionDescribe();
env->ExceptionClear();
sprintf(sbuf, "DLL: Exception while calling ChartFactory.getInstance()");
printSBufViaJava(sbuf);
return NULL;
mid = env->GetMethodID(chartFactoryClass, "getChartID", "(Ljava/nio/ByteBuffer;Ljava/nio/ByteBuffer;Ljava/nio/ByteBuffer;Ljava/nio/ByteBuffer;IIIIIII)F");
if (ex= env->ExceptionOccurred() ) {
env->ExceptionDescribe();
env->ExceptionClear();
sprintf(sbuf, "DLL: Cannot find method ID for ChartFactory.getChartID()\n");
printSBufViaJava(sbuf);
return NULL;
jobject symbolBuf=env->NewDirectByteBuffer(a_psDataRec->pszSymbol, strlen(a_psDataRec->pszSymbol) );
if (ex= env->ExceptionOccurred() ) {
env->ExceptionDescribe();
env->ExceptionClear();
sprintf(sbuf, "DLL: Cannot allocate symbolBuf\n");
printSBufViaJava(sbuf);
return NULL;
jobject securityNameBuf=env->NewDirectByteBuffer(a_psDataRec->pszSecurityName, strlen(a_psDataRec->pszSecurityName) );
if (ex= env->ExceptionOccurred() ) {
env->ExceptionDescribe();
env->ExceptionClear();
sprintf(sbuf, "DLL: Cannot allocate securityNameBuf\n");
printSBufViaJava(sbuf);
return NULL;
jobject securityPathBuf=env->NewDirectByteBuffer(a_psDataRec->pszSecurityPath, strlen(a_psDataRec->pszSecurityPath) );
if (ex= env->ExceptionOccurred() ) {
env->ExceptionDescribe();
env->ExceptionClear();
sprintf(sbuf, "DLL: Cannot allocate securityPathBuf\n");
printSBufViaJava(sbuf);
return NULL;
jobject securityOnlineSourceBuf=env->NewDirectByteBuffer(a_psDataRec->pszOnlineSource, strlen(a_psDataRec->pszOnlineSource) );
if (ex= env->ExceptionOccurred() ) {
env->ExceptionDescribe();
env->ExceptionClear();
sprintf(sbuf, "DLL: Cannot allocate onlineSourceBuf\n");
printSBufViaJava(sbuf);
return NULL;
// Java Function call leads to crash, if console output is turned off and
// the first statement in the Java routine is a (useless) string concatenation.
// Otherwise it works stable.
jfloat chartID=env->CallFloatMethod(chartFactory, mid, securityNameBuf, symbolBuf,
securityPathBuf, securityOnlineSourceBuf, (jint)(a_psDataRec->iPeriod),
(jint)(a_psDataRec->iInterval), (jint)(a_psDataRec->iStartTime),
(jint)(a_psDataRec->iEndTime), (jint)(a_psDataRec->iSymbolType),
(jint)firstDate, (jint)firstTime );
if (ex= env->ExceptionOccurred() ) {
env->ExceptionDescribe();
env->ExceptionClear();
sprintf(sbuf, "DLL: Exception while calling ChartFactory.getChartID()");
printSBufViaJava(sbuf);
return NULL;