Suspending and resuming JNI thread

[ganeshamutha]

Hi all,,


I am calling a C native methode from Java in new thread... The
C function calling and doing everthing fine.. since it is a long
process i want to quit some time before it is going to terminate
itself..

So, i created a window with start, pause, resume and stop
button...

when i click the start button, the C code executing
properly... since it is calling public void run(),

/* start .....
{
nativeclass.itisthread.start();

}

but when i calling .suspend() , .resume() for the
thread to make suspend and resume respectively it is not responding...
why?

Say examply... the C code..

for(;
{
printf("I am in C.....");
}


What my question is .. how can i suspend and resume JNI the
thread ... Please help me to solve this issue..

Thanks in Advance,
ganesh.

 

[Gordon Beaton]

What my question is .. how can i suspend and resume JNI the thread

Thread methods suspend(), resume() etc are deprecated:
http://java.sun.com/j2se/1.5.0/docs/guide/misc/threadPrimitiveDeprecation.html

At any rate, your native thread cannot be forced to suspend or exit,
it needs to *cooperate* with the controlling thread. The easiest way
is to periodically call a Java method that can wait on a semaphore.

One way is to create a new instance of the following class, to pass to
your native method:

public class Suspender {
private boolean cancelled = false;
private boolean suspended = false;

public synchronized boolean wait_here() {
try {
while (suspended) {
wait();
}
}
catch (InterruptedException e) {
cancelled = true;
}

return cancelled;
}

public synchronized void suspend() {
suspended = true;
}

public synchronized void resume() {
suspended = false;
notify();
}

public synchronized void cancel() {
cancelled = true;
resume();
}
}

From the native method, periodically call wait_here(). If the
controlling thread calls suspend(), the native thread will block in
the next call to wait_here(). When the controlling thread calls
resume(), the native thread will continue.

If the controlling thread calls cancel(), wait_here() will return
true, signalling the native method to return.

/gordon

 

[ganeshamutha]

i, Beaton

Thanku very much for ur reply, even though i not clear .... i am posted
sample code exactly what i am using...

/* Mynative Class***/

class Mynative implements Runnable
{
Thread t;
Mynative()
{ t=new Thread(this); }

public synchronized void run()
{
Cfun();
}
static System.loadLibrary("Clib");
}

/*MyGui Class***/
class GUI extends JDialog implements ActioinListener
{
Mynative mm=new Mynative();
/*Button creation and adding*/
public void actionPerformed(ActionEvent ee)
{
if(ee.getSource()==start)
mm.t.start(); //C execution started fine...
and printing in infinite loop
if(ee.getSource()==pause)
mm.t.suspend(); // no response... still
printing..
if(ee.getSource()==resume)
mm.t.resume(); // no response.. still printing
if(ee.getSource()==stop)
mm.t.stop(); // no response.. still
printing..
}
}


/*Main*/
public class Threadwindow
{
public static void main(String args[]) {
GUI window = new GUI();

window.setTitle("Process_Window");
window.pack();
window.show();
}
}


/*Cfun()----in C file--*/

JNIEXPORT void JNICALL Java_Mynative_Cfun (JNIEnv *env1, jobject
objj)
{
for(;
{ printf(" C code :..."); }
}


Please explain me .. how i have to change the code inorder to make
working of suspend, resume and stop with ur code...

Thanking u,
Ganesh

 

[Gordon Beaton]

Please explain me .. how i have to change the code inorder to make
working of suspend, resume and stop with ur code...

Create an instance of the Suspend class I posted earlier. Pass the
reference as an argument to your C function (you'll need to change the
native declaration and re-run javah).

Now change your C function, so that it occasionally invokes
susp.wait_here():

JNIEXPORT void JNICALL Java_Mynative_Cfun(JNIEnv *env1, jobject objj, jobject susp)
{
jclass cls = (*env)->GetObjectClass(env1, susp);
jmethodID mid = (*env)->GetMethodID(env1, cls, "wait_here", "()Z");

while (!(*env)->CallBooleanMethod(env1, susp, mid)) {
printf("C code...\n");
}

printf("Cancelled!\n");
return;
}

From elsewhere, call susp.suspend(), susp.resume(), or susp.cancel()
to control the native method.

/gordon

 

[ganeshamutha]

Thanku for explain.. but still i am not able to control....

I am calling the Native thread through start button by calling
mynative.thread.start();
C code also altered according to ur suggestion..
i am creating one more instance of Suspend at GUI class.. and
for wait i am calling the susp.wait() for suspend click... but it is
not responding... i am requesting u to please look my code of GUI and
Mynative class in my previous post...

one more question is...
here we are keep on checking in while (C code)... if the
program calling a one more c function(very lengthy)

ex,..

JNIEXPORT void JNICALL Java_Mynative_Cfun(JNIEnv *env1, jobject
objj, jobject susp)
{
a();
}

a()
{
.....
....
}

then how can i rewrite the C code or java code inorder to suspend
and resume , stop click work ..

Thanking u once again,
Ganesh.

 

[Gordon Beaton]

Thanku for explain.. but still i am not able to control.... [...]

then how can i rewrite the C code or java code inorder to suspend
and resume , stop click work ..

You need to be clearer and more specific about what isn't working, or
what you don't understand.

I don't know how to be any clearer in my explanation. In your C code,
you must call susp.wait_here() occasionally. If susp.suspend() has
been called, it cause susp.wait_here() to *block*. When susp.resume()
is later called, susp.wait_here() will return and the C function will
continue.

You don't need to call susp.wait_here() in a loop, but your original
example showed a loop. You just need to call it occasionally during
the lengthy operation.

I have shown you how to do all of these things. Now it's up to you to
understand how to put the pieces together in your application. Don't
ask me to write your code for you.

I can't help you debug the empty code fragments you've shown: "a()",
but please do not post a lengthy example either. Try to understand the
short example I posted earlier.

Here's a suggestion: try to make it work from Java, you don't need
native code to test this. Change the run() method to something like
this:

public synchronized void run() {
System.out.println("starting...");

while (!susp.wait_here()) {
System.out.println("hello, world");

try {
Thread.sleep(1000);
} catch (InterruptedException e) {
// ignored
}
}

System.out.println("cancelled");
}

i am creating one more instance of Suspend at GUI class.. and

Make sure you create exactly *one* instance of the Suspend object,
that is *shared* by both the GUI code and the native function.

Alternatively (and perhaps it's not a good idea to suggest
alternatives at this point) copy the four methods from Suspender.java
into your MyNative class instead. This way you don't need to create
any extra objects at all. Call mn.suspend(), mn.resume() from the GUI,
and mn.wait_here() from the C function.

/gordon

 

[ganeshamutha]

I am very clear now... i am following ur alternative apporach.. it is
seems to be very easy....

but sorry to say this... still i have problem...

When i click from GUI it is started and C printf working
fine....... but when i Click the suspend button the control not able to
coming out from button.. it is look like going into toggle mode.. even
JDialog's close button also not working....

What could be the proplem...... the infinite loop / thread
issue.. / some thing else.. Please how to rectify it....

Should i call the wait_here() function more then once in 'C' -
lengthly flow...


With many thanks,
Ganesh..


Gordon Beaton wrote:

Thanku for explain.. but still i am not able to control.... [...]

then how can i rewrite the C code or java code inorder to suspend
and resume , stop click work ..

You need to be clearer and more specific about what isn't working, or
what you don't understand.

I don't know how to be any clearer in my explanation. In your C code,
you must call susp.wait_here() occasionally. If susp.suspend() has
been called, it cause susp.wait_here() to *block*. When susp.resume()
is later called, susp.wait_here() will return and the C function will
continue.

You don't need to call susp.wait_here() in a loop, but your original
example showed a loop. You just need to call it occasionally during
the lengthy operation.

I have shown you how to do all of these things. Now it's up to you to
understand how to put the pieces together in your application. Don't
ask me to write your code for you.

I can't help you debug the empty code fragments you've shown: "a()",
but please do not post a lengthy example either. Try to understand the
short example I posted earlier.

Here's a suggestion: try to make it work from Java, you don't need
native code to test this. Change the run() method to something like
this:

public synchronized void run() {
System.out.println("starting...");

while (!susp.wait_here()) {
System.out.println("hello, world");

try {
Thread.sleep(1000);
} catch (InterruptedException e) {
// ignored
}
}

System.out.println("cancelled");
}

i am creating one more instance of Suspend at GUI class.. and

Make sure you create exactly *one* instance of the Suspend object,
that is *shared* by both the GUI code and the native function.

Alternatively (and perhaps it's not a good idea to suggest
alternatives at this point) copy the four methods from Suspender.java
into your MyNative class instead. This way you don't need to create
any extra objects at all. Call mn.suspend(), mn.resume() from the GUI,
and mn.wait_here() from the C function.

/gordon

 

[Gordon Beaton]

When i click from GUI it is started and C printf working
fine....... but when i Click the suspend button the control not able
to coming out from button.. it is look like going into toggle
mode.. even JDialog's close button also not working....

Post the code. I can't help you with the GUI but perhaps someone else
can.

Should i call the wait_here() function more then once in 'C' -
lengthly flow...

Call it everywhere you are willing or able to be suspended.

/gordon

 

[ganeshamutha]

Thanku so much for suggestions... now i am able to suspend,resume, the
C-core since i checking periodically in while loop... (ie, we are
checking the suspend bool)..

GUI is also very perfect after i removed the synchronized keyword in
ur suspend call...

now i have few more questions...

Please tell me if C - code written with many function , like,

JNIEXPORT void JNICALL Java_Mynative_Cfun(JNIEnv *env1, jobject
objj, jobject susp)
{
a();
}

a()
{
.....
....
b();
}

b () { ..... ....... c()}

c()
{
// how can i call the "wait_here", here..
}

can i able to pass the JNIEnv *env1 pointer to each functions
argument.. else can i declare JNIEnv as a globel variable and from the
extern keyword wait_here() can i able call... Please help me solve
this little conflict... Please tell me if there any other best way to
access the wait_here() function in c() function..

b(), c() are modules each written in different .c files those are
included very perfectly...

Thanks again,
Ganesh