[logback-user] Blocked threads waiting for logback SiftingAppender on WebLogic

Артём Тарасов arttaras at gmail.com
Thu Jun 6 14:07:35 CEST 2013

I have one problem with performance in production because of, as I think,
blocked threads .

When I got thread dumps from production environment I was surprised that
about 50% of thread are in status:

*-- Blocked trying to get lock:
ch/qos/logback/classic/sift/SiftingAppender at 0x1111fe3e8[unlocked]*

At the same time, as you can see, SiftingAppender is 'unlocked'.

I have no idea why it's happened.

If we deep into logback sources we will find there a synchronized method
which is the 'thin' place I think:

public synchronized void doAppend(E eventObject) {
    // WARNING: The guard check MUST be the first statement in the
    // doAppend() method.

    // prevent re-entry.
    if (guard) {
    ...  }

We use weblogic v.

slf4j.version - 1.7.5

logback.version - 1.0.13

Has anybody ideas why it's happened and how to avoid this problem?
It may be not logback's problem. I now trying to find resolution only.
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