When you run logging into same file from many threads on a system that has more than one physical processor (Dual Core for example), a deadlock will occur after a while. This can not be reproduced on HyperThreading processors. Here's an example program that will demonstrate the behavior:

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Main.java
-----------------------------

import java.util.Date;
import java.util.concurrent.ScheduledThreadPoolExecutor;
import java.util.concurrent.TimeUnit;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import ch.qos.logback.classic.LoggerContext;
import ch.qos.logback.classic.joran.JoranConfigurator;
import ch.qos.logback.core.joran.spi.JoranException;

public class Main extends Thread
{
private final static String LOGGER_CONFIGURATION_FILE = "logger.xml";
private final Logger logger = LoggerFactory.getLogger(Main.class);

private final long start;

public Main()
throws JoranException

{ start = new Date().getTime(); LoggerContext lc = (LoggerContext)LoggerFactory.getILoggerFactory(); JoranConfigurator configurator = new JoranConfigurator(); lc.shutdownAndReset(); configurator.setContext(lc); configurator.doConfigure(LOGGER_CONFIGURATION_FILE); }

public void start()

{ ScheduledThreadPoolExecutor ex1 = new ScheduledThreadPoolExecutor(1); ScheduledThreadPoolExecutor ex2 = new ScheduledThreadPoolExecutor(1); ScheduledThreadPoolExecutor ex3 = new ScheduledThreadPoolExecutor(1); ScheduledThreadPoolExecutor ex4 = new ScheduledThreadPoolExecutor(1); ScheduledThreadPoolExecutor ex5 = new ScheduledThreadPoolExecutor(1); ex1.scheduleAtFixedRate(new Task("EX1"), 10, 10, TimeUnit.MICROSECONDS); ex2.scheduleAtFixedRate(new Task("EX2"), 10, 10, TimeUnit.MICROSECONDS); ex3.scheduleAtFixedRate(new Task("EX3"), 10, 10, TimeUnit.MICROSECONDS); ex4.scheduleAtFixedRate(new Task("EX4"), 10, 10, TimeUnit.MICROSECONDS); ex5.scheduleAtFixedRate(new Task("EX5"), 10, 10, TimeUnit.MICROSECONDS); super.start(); }

public void run()
{
try
{
while(true)
{
logger.debug("[MAIN] {}", new Date().getTime() - start);
Thread.sleep(10);
}
}
catch (InterruptedException e)
{
logger.info("[MAIN]: Interrupted: {}", e.getMessage());
}
}

public static void main(String[] args)
{
try

{ Main main = new Main(); main.start(); }

catch (JoranException e)

{ System.out.println("Failed to load application: " + e.getMessage()); }

}
}

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Task.java
-------------------------------

import java.util.Date;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

public class Task implements Runnable
{
private final Logger logger = LoggerFactory.getLogger(Task.class);
private final Logger logger_main = LoggerFactory.getLogger(Main.class);
private final String name;
private final long start;

public Task(final String name)

{ this.name = name; start = new Date().getTime(); }

public void run()
{
logger.debug("[{}] {}", name, new Date().getTime() - start);
logger_main.debug("[MAIN] - [{}] {}", name, new Date().getTime() - start);
}
}