Deadlock... i think

[Carsten H. Pedersen]

I apologize in advance for the length of the note, and the source code
included.

I posted earlier under the title "Double streams", where i wanted to
use an RMI object as a sort of proxy for two clients to exchange data
via streams. I kinda failed, but now i'm trying something new. This
doesn't work either, but this time i think someone might be able to
solve it, since i'm not adept at using threads and i think that's
where the problem is. :)

The source for ByteHolder and RemoteByteHolde r is included below. A
server is run, making a ByteHolder, BH, available via RMI.

Client A obtains the reference to BH, and passes this on to its
FooOutputStream , which extends OutputStream and implements the
write(int b) method by calling putByte(b) on BH.

Client B also gets BH, passes this to FooInputStream, which extends
InputStream and implements read() by calling getByte() on BH.

What i did to test was:
- run the server
- client A wraps the FooOutputStream in a PrintWriter, and
println("foo") is called on it
- client B wraps FooInputStream in a InputStreamRead er, which is
then wrapped in a BufferedReader, and readLine() is called on that

The data then goes, one byte at the time, from client A to client B.
Client A stops running, but Client B just sorta hangs around... in a
deadlock i presume. I can make it return and print out the read line
by doing one of two things:
- kill the server
- manually send a -1 to client B

When i've used streams before, i didn't have to send a -1 in order to
get the reading side to get on with it - it just happened magically. I
also don't understand why killing the server make things better...

Can anyone explain this or, as an alternative, suggest a better way to
exchange bytes via RMI. I just really wanted to make streams work. :)

Oh, another thing. To make the server available, i've made it Runnable
and in the run i have a while(true) loop, that makes the thread sleep
for a chunk of time. Maybe that is a problem, too?

Regards,
Carsten H. Pedersen
----------- SOURCE BELOW -------------
package streams.holder;

import java.rmi.Remote ;
import java.rmi.Remote Exception;

public interface RemoteByteHolde r extends Remote {
int getByte() throws RemoteException ;
void putByte(int b) throws RemoteException ;
}

....

package streams.holder;
import java.rmi.Remote Exception;

public class ByteHolder implements RemoteByteHolde r {

private int theByte;
private boolean stored = false;

public synchronized int getByte() throws RemoteException {
while(!stored) {
try {
wait();
} catch (InterruptedExc eption e) {
// TODO Auto-generated catch block
e.printStackTra ce();
}
}

System.out.prin tln("hb: get: "+theByte);
int i = theByte;
stored = false;
notifyAll();
return i;
}

public synchronized void putByte(int b) throws RemoteException {
while(stored) {
try {
wait();
} catch (InterruptedExc eption e) {
// TODO Auto-generated catch block
e.printStackTra ce();
}
}

System.out.prin tln("bh: put: "+b);
stored = true;
theByte = b;
notifyAll();
}

}

[Oliver Wong]

"Carsten H. Pedersen" <[e-mail]> wrote in message
news:43******** *************** @dreader2.cyber city.dk...

I posted earlier under the title "Double streams", where i wanted to use
an RMI object as a sort of proxy for two clients to exchange data via
streams. I kinda failed, but now i'm trying something new. This doesn't
work either, but this time i think someone might be able to solve it,
since i'm not adept at using threads and i think that's where the problem
is. :)

If you don't get any answers for 1 or 2 days, try posting this to
comp.lang.java. programmer. There's a lot of people there who are familiar
with threading who don't read this newsgroup.

If you post there too early though, you get accused of multiposting.

- Oliver

[Godspeed]

Hi Carsten,

What does your readLine code look like?

Are you doing something like:

while ((line = readLine())!=nu ll) ...
"Carsten H. Pedersen" <[e-mail]> wrote in message
news:43******** *************** @dreader2.cyber city.dk...

I apologize in advance for the length of the note, and the source code
included.

I posted earlier under the title "Double streams", where i wanted to use
an RMI object as a sort of proxy for two clients to exchange data via
streams. I kinda failed, but now i'm trying something new. This doesn't
work either, but this time i think someone might be able to solve it,
since i'm not adept at using threads and i think that's where the problem
is. :)

The source for ByteHolder and RemoteByteHolde r is included below. A server
is run, making a ByteHolder, BH, available via RMI.

Client A obtains the reference to BH, and passes this on to its
FooOutputStream , which extends OutputStream and implements the write(int
b) method by calling putByte(b) on BH.

Client B also gets BH, passes this to FooInputStream, which extends
InputStream and implements read() by calling getByte() on BH.

What i did to test was:
- run the server
- client A wraps the FooOutputStream in a PrintWriter, and println("foo")
is called on it
- client B wraps FooInputStream in a InputStreamRead er, which is then
wrapped in a BufferedReader, and readLine() is called on that

The data then goes, one byte at the time, from client A to client B.
Client A stops running, but Client B just sorta hangs around... in a
deadlock i presume. I can make it return and print out the read line by
doing one of two things:
- kill the server
- manually send a -1 to client B

When i've used streams before, i didn't have to send a -1 in order to get
the reading side to get on with it - it just happened magically. I also
don't understand why killing the server make things better...

Can anyone explain this or, as an alternative, suggest a better way to
exchange bytes via RMI. I just really wanted to make streams work. :)

Oh, another thing. To make the server available, i've made it Runnable and
in the run i have a while(true) loop, that makes the thread sleep for a
chunk of time. Maybe that is a problem, too?

Regards,
Carsten H. Pedersen
----------- SOURCE BELOW -------------
package streams.holder;

import java.rmi.Remote ;
import java.rmi.Remote Exception;

public interface RemoteByteHolde r extends Remote {
int getByte() throws RemoteException ;
void putByte(int b) throws RemoteException ;
}

...

package streams.holder;
import java.rmi.Remote Exception;

public class ByteHolder implements RemoteByteHolde r {

private int theByte;
private boolean stored = false;

public synchronized int getByte() throws RemoteException {
while(!stored) {
try {
wait();
} catch (InterruptedExc eption e) {
// TODO Auto-generated catch block
e.printStackTra ce();
}
}

System.out.prin tln("hb: get: "+theByte);
int i = theByte;
stored = false;
notifyAll();
return i;
}

public synchronized void putByte(int b) throws RemoteException {
while(stored) {
try {
wait();
} catch (InterruptedExc eption e) {
// TODO Auto-generated catch block
e.printStackTra ce();
}
}

System.out.prin tln("bh: put: "+b);
stored = true;
theByte = b;
notifyAll();
}

}