[logback-dev] [JIRA] Commented: (LBCORE-63) Deadlock when running on multiple core processors

[Ralph Goers (JIRA)]

    [ http://jira.qos.ch/browse/LBCORE-63?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=10902#action_10902 ] 

Ralph Goers commented on LBCORE-63:
-----------------------------------

I should point out, this isn't a deadlock but a bottleneck. By removing the locking in Logback we allow Appenders to better handle situations like this. But to do that the Appender will have to extend UnsynchronizedAppenderBase, which the SocketAppender doesn't do. Even if it did, because the SocketAppender has a scarce resource, the socket, it would eventually have to block on that. 

The SocketAppender could be modified to use a pool of sockets, but then you would just end up with a bunch of threads sitting in SocketWrite. The advantage is that if the sockets have a 5 second timeout and you have 10 threads then the average log event takes 50 seconds. With a socket pool the same size as the number of threads the average log event would be 5 seconds. Still awful but 10 times better.

What is needed is a better way to handle Appenders that are "Out of Service".  I will create a Jira issue for that and create a patch at some point.

> Deadlock when running on multiple core processors
> -------------------------------------------------
>
>                 Key: LBCORE-63
>                 URL: http://jira.qos.ch/browse/LBCORE-63
>             Project: logback-core
>          Issue Type: Sub-task
>    Affects Versions: 0.9.9
>         Environment: Operating System: Windows
> Platform: PC
>            Reporter: Toni Heimala
>            Assignee: Ceki Gulcu
>            Priority: Blocker
>         Attachments: patch.txt, patch2.txt, patch3.txt
>
>
> 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:
> -----------------------------
> 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());
>         }
>     }
> }
> -------------------------------
> 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);
>     }
> }

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