Problem with JNI and Tomcat


E

Elvandar

Hi all.
I developed a JNI DLL to use with a Java Web Application.
This DLL is used to communicate over a RS232 port, and it must notice
any event that occurs on the port to the java application.
I tested it before with a Standalone app to make sure all works, and
then moved it to the web application. The problem is that in the
standalone app it's all ok, whilst in the web app I'm only able to call
JNI functions from java, but I can't call java methods from the JNI
DLL...here is the code involved, if you have any idea on how to solve
this problem is very appreciated!!!

The sequence of operations is the following:

1) From it.ribes.serialDriver.SerialPort class i call the
nativeOpenPort JNI function
2) the nativeOpenPort functions looks for the "notifyEvent" Java method
in the object that called it, in order to notify events when they
occurs, and saves it in the "eventNotifyMethod" of the SERIALPORT
structure
3) When an event occurs, the thread used for reception calls the
"notifyEvent" function in the DLL, which calls the Java method searched
in the step 2

The CSerialEx Class istansiate a thread which "listens" to the serial
port waiting for events, and when an event occurs calls the
"notifyEvent" in the DLL.

Thanks for any help, I'm a bit desperate... :(


==========
JAVA
==========

--- SerialPort.java ---

public class SerialPort extends CommPort {
SerialPortEventNotifier notifier;

...

private native boolean nativeOpenPort(String port);

/* Called from JNI DLL */
private void notifyEvent(int eventType) {
notifier.notifyEvent(eventType);
}
/* *********** */

boolean open(int timeout) {
return nativeOpenPort(this.port);
}

...

}


--- CommPortIdentifier.java ---

public class CommPortIdentifier {
static List portList = new LinkedList();

public static final int PORT_SERIAL = 1;

private String portName;
private int portType;

static {
System.loadLibrary("RS232Driver_DLL");
}

private static native boolean nativeTestSerial(int port);

public CommPort open(String application, int timeout) throws
PortInUseException {
SerialPort serialPort = new SerialPort(this.portName);
if(!serialPort.open(timeout))
throw new PortInUseException(portName);
return serialPort;
}

...

}

=============
JNI DLL
=============

--- it_ribes_serialDriver_serialPort.cpp ---

....

typedef struct
{
CSerialEx *com;
char port[10];
jobject javaEventManager;
jmethodID eventNotifyMethod;
LPSTR rxBuffer;
int rxBufferDim;
int inputIndex;
int outputIndex;
int dataAvailable;
HANDLE readingMutex;
int rxTimeout;
DWORD eventMask;
} SERIALPORT, *LPSERIALPORT;


/* This method is used to open the serial port */
JNIEXPORT jboolean JNICALL
Java_it_ribes_serialDriver_SerialPort_nativeOpenPort (JNIEnv *env,
jobject jobj, jstring port)
{
LPSERIALPORT SerialPort = (LPSERIALPORT)malloc(sizeof(SERIALPORT));

if(VM == NULL)
env->GetJavaVM(&VM);

LPSTR comPort = (LPSTR)env->GetStringUTFChars(port, 0);

_strupr(comPort);
strncpy(SerialPort->port,comPort,10);
SerialPort->com = new CSerialEx(); // This is the class used to
communicate over the serial port (Overlapped I/O used)

SerialPort->com->Open(comPort,0,0,true);
SerialPort->javaEventManager = env->NewGlobalRef(jobj);
jclass cls = env->GetObjectClass(SerialPort->javaEventManager);
SerialPort->eventNotifyMethod =
env->GetMethodID(cls,"notifyEvent","(I)V");

env->ReleaseStringUTFChars(port, comPort);

return TRUE;
}

/* This method is called from the CSerialEx class to notify an event */
void NotifyEvent(CSerial::EEvent event, LPSTR port)
{
void *voidenv = NULL;
JNIEnv *env;

LPSERIALPORT SerialPort = SearchSerialPort(port);
int javaEvent = MapEvent(event);

VM->AttachCurrentThread(&voidenv,NULL);
env = (JNIEnv *)voidenv;

if(javaEvent != 0)
{
env->CallVoidMethod(SerialPort->javaEventManager,
SerialPort->eventNotifyMethod, javaEvent);
}

VM->DetachCurrentThread();
}

....
 
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E

Elvandar

Elvandar pretended :
Hi all.
I developed a JNI DLL to use with a Java Web Application.
This DLL is used to communicate over a RS232 port, and it must notice any
event that occurs on the port to the java application.
I tested it before with a Standalone app to make sure all works, and then
moved it to the web application. The problem is that in the standalone app
it's all ok, whilst in the web app I'm only able to call JNI functions from
java, but I can't call java methods from the JNI DLL...here is the code
involved, if you have any idea on how to solve this problem is very
appreciated!!!

[CUT]

If it could be useful, I use Java 1.4.2 and Tomcat 5.0.28.
 
G

Gordon Beaton

Java_it_ribes_serialDriver_SerialPort_nativeOpenPort (JNIEnv *env,
jobject jobj, jstring port)
{
LPSERIALPORT SerialPort = (LPSERIALPORT)malloc(sizeof(SERIALPORT));

The above can't be right... SerialPort is local to this method and not
stored elsewhere. How do you expect to find it later? Please post
*real* code.

In your callback method, have you confirmed that SerialPort != NULL,
(see prev), that (javaEvent != 0), etc, i.e. that you actually *reach*
CallVoidMethod()?

If so, what does CallVoidMethod() return? What do
env->ExceptionOccurred() and env->ExceptionDescribe() say?

This might also help:
http://groups.google.com/group/comp.lang.java.programmer/msg/511c52ef88a993c9

/gordon

--
 
E

Elvandar

Gordon Beaton was thinking very hard :
The above can't be right... SerialPort is local to this method and not
stored elsewhere. How do you expect to find it later? Please post
*real* code.

Sorry, I cleaned up a bit the code I posted because the function was
too long, and I suppose I deleted a too much :p. In nativeOpenPort
there was also the instruction "AddSerialPort(SerialPort);" that adds
the object to a list of the current opened ports (see below), and
retrieved in the notifyEvent method with the SearchSerialPort function.

void AddSerialPort(LPSERIALPORT SerialPort)
{
LPPORTLIST newPort = (LPPORTLIST)malloc(sizeof(PORTLIST));

newPort->ComPort = SerialPort;
newPort->Next = openedPorts;
openedPorts = newPort;
}
In your callback method, have you confirmed that SerialPort != NULL,
(see prev), that (javaEvent != 0), etc, i.e. that you actually *reach*
CallVoidMethod()?
Yes


If so, what does CallVoidMethod() return? What do
env->ExceptionOccurred() and env->ExceptionDescribe() say?

The java method sometimes seems to be correctly called (no exceptions
thrown), but the data it retrieves is absolutely incorrect. The problem
is that most of times it is not called, but if I open a serial terminal
all data arrived and bufferized is correctly shown on screen...and if I
run the same DLL in a java standalone app all works correctly, the
problem only happens if I load the DLL under tomcat...

Seen it. My jar library is located under %CATALINA_HOME%\shared\lib,
and in my tests (just to avoid problems of this kind) I restarted
tomcat every time.

Thanks for your help.
 
G

Gordon Beaton

The java method sometimes seems to be correctly called (no
exceptions thrown), but the data it retrieves is absolutely
incorrect. The problem is that most of times it is not called, but
if I open a serial terminal all data arrived and bufferized is
correctly shown on screen...and if I run the same DLL in a java
standalone app all works correctly, the problem only happens if I
load the DLL under tomcat...

Have you confirmed that the data is correct when it reaches the native
callback method, before you call Java?

Have you attempted hardcoding some test data there?

You don't seem to be initializing all of the SerialPort fields.
Remember that memory returned by malloc() is *not* zeroed, and the
actual contents may differ in the different runtime environments.

Hmm, yes I see now that that was you too...

/gordon

--
 
E

Elvandar

Gordon Beaton wrote on 10/04/2007 :
Have you confirmed that the data is correct when it reaches the native
callback method, before you call Java?

Have you attempted hardcoding some test data there?

I find out the problem is not located in my code and/or in something
linked to tomcat. Even if in standalone applications all works well,
the problem is linked with the GSM modem I'm currently using (a Siemens
M20). With other modems (also of the Siemens family, like the TC35) or
simulating a modem on a loopback link, all works well.

Thanks for your help, I'll try to check why the M20 is so hard to
handle :)
 
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C

Chris Uppal

Elvandar said:
The java method sometimes seems to be correctly called (no exceptions
thrown), but the data it retrieves is absolutely incorrect. The problem
is that most of times it is not called, but if I open a serial terminal
all data arrived and bufferized is correctly shown on screen...and if I
run the same DLL in a java standalone app all works correctly, the
problem only happens if I load the DLL under tomcat...

The only possibilities I can think of (that you haven't already ruled out) are
that either the machine is running under a higher load with Tomcat (and so may
be missing asynchronous notifications somewhere), or that the threading
environment is different.

I'm a little bit suspicious of the calls to AttachCurrentThread() and
DetachCurrentThread() in your NotifyEvent(). If that is being called at
serial port speeds, and if I'm right in thinking that AttachCurrentThread() is
a relatively heavyweight operation when the thread is not already attached[*],
then that /might/ a source of problems.

-- chris

[*] AFAIK it involves messing around with the target thread's stack.
 

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