NOTE

Collections.synchronizedMap

Synchronized Map wrappers, compound-operation atomicity, iteration locking, and concurrent alternatives.

JavaCreated 01/17/2020Updated 09/15/20261 min readhistorical

This is a historical learning note and may contain outdated or incomplete understanding.

Collections.synchronizedMap(map) serializes individual map operations on a wrapper mutex.

Compound logic such as “if absent, then put” still needs one synchronized critical section unless an atomic map operation is used. Iteration over views such as keySet() also requires the documented external synchronization.

For scalable shared access, ConcurrentHashMap normally provides a better concurrency model and atomic operations such as computeIfAbsent.