lhotari commented on code in PR #25367:
URL: https://github.com/apache/pulsar/pull/25367#discussion_r3101546500
##########
pulsar-common/src/main/java/org/apache/pulsar/common/naming/TopicName.java:
##########
@@ -77,12 +77,32 @@ public static TopicName get(String domain, String tenant,
String namespace, Stri
return TopicName.get(name);
}
+ /**
+ * Get or create a TopicName from the cache.
+ *
+ * <p>Optimization over {@code computeIfAbsent}: avoids holding the
ConcurrentHashMap bin-lock
+ * while constructing a new TopicName object. The construction (string
splitting / parsing) is
+ * pure CPU work and can be done outside the lock. In the typical
steady-state (cache hit) this
+ * method does a single volatile read via {@code get()} and returns
immediately with no
+ * synchronization overhead.
+ *
+ * <p>In the cache-miss case, two threads racing on the same key may both
construct a
+ * {@code TopicName} instance, but only one wins the {@code putIfAbsent}
and the loser's
+ * instance is simply discarded. This is safe because {@code TopicName} is
immutable and
+ * construction is cheap compared to the lock-contention / context-switch
cost of
+ * {@code computeIfAbsent}.
Review Comment:
these details could be in code comments since the public API user shouldn't
need to know about the implementation details.
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