Locking contention on com.cognitect.transit.impl.Cache

[wilkerlucio]

Hello,

During a performance tuning task, we notice a high locking time on com.cognitect.transit.impl.Cache during service startup.

I tracked it down to this code snippet:

transit-java/src/main/java/com/cognitect/transit/impl/WriterFactory.java

Lines 27 to 33 in 8c29b1c

	synchronized (handlerCache) {
	writeHandlerMap = handlerCache.get(customHandlers);
	if (writeHandlerMap == null) {
	writeHandlerMap = new WriteHandlerMap(customHandlers);
	handlerCache.put(customHandlers, writeHandlerMap);
	}
	}

Without changing the library itself, I wrapped our write handlers here with a WriteHandlerMap class to avoid that block, getting into this code path instead:

transit-java/src/main/java/com/cognitect/transit/impl/WriterFactory.java

Lines 23 to 24 in 8c29b1c

	if (customHandlers instanceof WriteHandlerMap)
	return new WriteHandlerMap(customHandlers);

Doing so significantly improved our locking times; in comparable scenarios, it dropped from 53 minutes of locking time on com.cognitect.transit.impl.Cache to 1 minute and 30 seconds.

I think if we can improve this locking block, maybe replacing it with a ConcurrentHashMap or something else that avoids global locking, we may be able to improve transit performance in high concurrency scenarios.

[puredanger]

Fixed by #45