Performance improvement in Category callAppenders()

[lauredogit]

Hi,

We just got a bottleneck in production with 2000+ threads blocked waiting on the lock in the synchronized block of callAppenders() in Category.

This never happend before to us, including in stress tests.

However, I seem to think a small performance improvement could be made with a simple open call (if I'm reading the code correctly).

    public void callAppenders(LoggingEvent event) {
	int writes = 0;

	for (Category c = this; c != null; c = c.parent) {
	    // Protected against simultaneous call to addAppender, removeAppender,...
        // open call, read the values under lock:
        AppenderAttachableImpl aai;
        boolean additive;
	    synchronized (c) {
            aai = c.aai;
            additive = c.additive;
        }
        // open call
        if (aai != null) {
            writes += aai.appendLoopOnAppenders(event);
        }
        if (!additive) {
            break;
        }
    }

Since aai is final and is a thread-safe data structure, we only want correct visibility of the aai and additive fields and we don't need to block the whole category object while calling appendLoopOnAppenders.

What do you think?

Best regards,
Dominique

[ceki]

@lauredogit Which version of reload4j are you using?

[lauredogit]

Production was using in 1.2.20.

[lauredogit]

It appears the threads were piling up due to slowness induced by a remote diagnostic agent running at the time (RDA).

It is strange that it materialized by showing a bottleneck in the synchronized block of Category#callAppenders().

Nonetheless, it might be a performance improvement to use an open call to invoke the appendLoopOnAppenders(...) method instead of doing it while holding the lock.