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Java port of a concurrent trie hash map implementation from the Scala collections library
Latest commit 1810db5 Sep 19, 2014 @romix Merge pull request #19 from rovarga/lower-count
Lower number of entries we hold during the test


This is a Java port of a concurrent trie hash map implementation from the Scala collections library. It is almost a line-by-line conversion from Scala to Java.

Idea + implementation techniques can be found in these reports written by Aleksandar Prokopec:

The original Scala implementation can be found here and is a part of scala.collection.concurrent:

Some of the tests and implementation details were borrowed from this project:

Implementation status :

  • The given implementation is complete and implements all features of the original Scala implementation including support for snapshots.
  • Wherever necessary, code was adapted to be more easily usable in Java, e.g. it returns Objects instead of Option as many methods of Scala's collections do.
  • This class implements all the ConcurrentMap & Iterator methods and passes all the tests. Can be used as a drop-in replacement for usual Java maps, including ConcurrentHashMap.

What is a concurrent trie hash map also known as ctrie?

ctrie is a lock-Free Concurrent Hash Array Mapped Trie.

A concurrent hash-trie or Ctrie is a concurrent thread-safe lock-free implementation of a hash array mapped trie.

It is used to implement the concurrent map abstraction. It has particularly scalable concurrent insert and remove operations and is memory-efficient.

It supports O(1), atomic, lock-free snapshots which are used to implement linearizable lock-free size, iterator and clear operations. The cost of evaluating the (lazy) snapshot is distributed across subsequent updates, thus making snapshot evaluation horizontally scalable.

The original Scala-based implementation of the Ctrie is a part of the Scala standard library since the version 2.10.

More info about Ctries:


This library is licensed under the Apache 2.0 license.


Usage of this library is very simple. Simply import the class com.romix.scala.collection.concurrent.TrieMap and use it as a usual Map.

import com.romix.scala.collection.concurrent.TrieMap;

Map myMap = new TrieMap <Object, Object> ();
myMap.put("key", "value");

Building the library

Use a usual mvn clean install

Using the library with Maven projects

The prebuilt binaries of the library are available from Maven central. Please use the following dependency in your POM files:


External dependencies

This library is self-contained. It does not depend on any additional libraries. In particular, it does not require the rather big Scala's standard library to be used.

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