I've recently started seeing this warning popping up in my Jenkins system log:
Feb 12, 2016 3:26:43 PM WARNING jenkins.metrics.util.HealthChecksThreadPool dropOldestInQueue
Too many health check executions queued, dropping oldest one. This may mean some health checks are taking too long to execute: jenkins.metrics.util.HealthChecksThreadPool@3cf11acf[Running, pool size = 0, active threads = 0, queued tasks = 0, completed tasks = 503], queue size=1, health checks=[disk-space, plugins, temporary-space, thread-deadlock] (4) [java.util.concurrent.FutureTask@8afd366]
Feb 12, 2016 3:26:43 PM WARNING com.codahale.metrics.health.HealthCheckRegistry runHealthChecks
Error executing health check thread-deadlock
I only noticed it today but I look at the logs every couple of days at least, and I haven't seen it until now. A Google search doesn't return any other instances of it appearing, so beyond a quick glance at the source code I can't say for sure what's causing it. As a one time thing I'd write it off but I'm seeing it repeated every couple of minutes following my last reboot. Should I be concerned about this?