<div dir="ltr">Hi, <div><br></div><div>We are using Logback 1.1.3, and observed through jstack that quite a few threads were blocked in OutputStreamAppender.subAppend waiting to obtain the lock.</div><div><br></div><div>This is a Play Framework app running in a dockerized environment, configured to log to STDOUT and papertrail.</div><div><br></div><div>Stack trace:<br></div><div><br></div><div><div>"New I/O worker #23" #75 prio=5 os_prio=0 tid=0x00007f6fc9764000 nid=0xaa waiting for monitor entry [0x00007f6edd3e7000]</div><div>   java.lang.Thread.State: BLOCKED (on object monitor)</div><div><span class="" style="white-space:pre">      </span>at ch.qos.logback.core.OutputStreamAppender.subAppend(OutputStreamAppender.java:211)</div><div><span class="" style="white-space:pre">       </span>- waiting to lock <0x00000000ab0f8f50> (a ch.qos.logback.core.spi.LogbackLock)</div><div><span class="" style="white-space:pre">       </span>at ch.qos.logback.core.OutputStreamAppender.append(OutputStreamAppender.java:103)</div><div><span class="" style="white-space:pre">  </span>at ch.qos.logback.core.UnsynchronizedAppenderBase.doAppend(UnsynchronizedAppenderBase.java:88)</div><div><span class="" style="white-space:pre">     </span>at ch.qos.logback.core.spi.AppenderAttachableImpl.appendLoopOnAppenders(AppenderAttachableImpl.java:48)</div><div><span class="" style="white-space:pre">    </span>at ch.qos.logback.classic.Logger.appendLoopOnAppenders(Logger.java:273)</div><div><span class="" style="white-space:pre">    </span>at ch.qos.logback.classic.Logger.callAppenders(Logger.java:260)</div><div><span class="" style="white-space:pre">    </span>at ch.qos.logback.classic.Logger.buildLoggingEventAndAppend(Logger.java:442)</div><div><span class="" style="white-space:pre">       </span>at ch.qos.logback.classic.Logger.filterAndLog_0_Or3Plus(Logger.java:396)</div><div><span class="" style="white-space:pre">   </span>at <a href="http://ch.qos.logback.classic.Logger.info">ch.qos.logback.classic.Logger.info</a>(Logger.java:600)</div><div><span class="" style="white-space:pre">       </span>at play.api.LoggerLike$<a href="http://class.info">class.info</a>(Logger.scala:93)</div><div><span class="" style="white-space:pre">   </span>at play.api.Logger$.info(Logger.scala:167)</div></div><div><br></div><div>Any suggestions on what may be going on here?</div><div><br></div><div>Thanks </div><div>-greg</div></div>