On Thu, 2003-12-18 at 07:56, Ceki GÃlcà wrote:
> >class State {
> > Logger log;
> >
> > synchronized void setState() {
> > // Something takes a long time here
> > log.debug("hello world");
> > }
> >
> > synchronized Object getState() {
> > }
> >
> > public String toString() {
> > return "state=" + getState();
> > }
> >}
>
> The above scenario is quite special. It is yet unclear if the deadlock
> observed by Prithi is related.
Well, that's the sort of scenario that I have run into, under load while
having debugging on. I have run into it under JBoss with the JBoss
classloader. I have run into it in a open source library. If you are
doing any sort of multi-threaded programming with logging under multiple
threads, I have been able to reproduce this deadlock every time.
If you don't plan to fix this issue, you should at least make a note
about the problem.
Here's a program which will reproduce the deadlock. There is nothing
special about this program:
import org.apache.log4j.Logger;
public class Deadlock {
static final Logger log = Logger.getLogger(Deadlock.class);
String var;
public synchronized void setVar(String var) {
log.debug(this);
}
public synchronized String getVar() {
return var;
}
public String toString() {
return "Value x=" + getVar();
}
public static void main(String args[]) throws Exception {
final Deadlock d = new Deadlock();
new Thread() {
public void run() {
while (true) log.debug(d);
}
}.start();
new Thread() {
public void run() {
while (true) d.setVar("n");
}
}.start();
}
}
You also need this log4j.properties file:
# Log4j configuration for unit tests
log4j.rootCategory=debug, R
log4j.appender.R=org.apache.log4j.RollingFileAppender
log4j.appender.R.File=deadlock.log
log4j.appender.R.layout=org.apache.log4j.PatternLayout
log4j.appender.R.layout.ConversionPattern=%d [%t] %-5p (%C:%M) - %m%n
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