I’m using cache2k 2.0.0.Final.

In org.cache2k.processor.EntryProcessor, I see the code:

        try {
          R result = processor.process(mutableEntry);
          c.result(result);
        } catch (WantsDataRestartException rs) {
          c.wantData();
          return;
        } catch (NeedsLockRestartException ex) {
          needsLock = true;
          c.wantData();
          return;
        } catch (Throwable t) {
          c.failure(new EntryProcessingException(t));
          return;
        }

So it's code were exception are used as flow control. But it's usually a bad idea, see https://shipilev.net/blog/2014/exceptional-performance/ for a deep analysis of that.

For example, when generating flamegraph for some of my code, I get the following result:

Most of the time is spent filling in the stack trace.

The code that generate this stack can be found at NettyNameResolver.java

Performance could be increased I think if both WantsDataRestartException and NeedsLockRestartException (and perhaps other) were static and not saving the stack.

This constructor can be used for that:

protected Exception(String message,
                    Throwable cause,
                    boolean enableSuppression,
                    boolean writableStackTrace)

If writableStackTrace is set to false, the stack trace is not saved.