Concurrency - Java 8 Recipes - page 343

Random random = new Random();
private void startUpdateThread(int i, final
ConcurrentMap<Integer, String> concurrentMap) {
Thread thread = new Thread(() -> {
while (!Thread.interrupted()) {
int randomInt = random.nextInt(20);
concurrentMap.put(randomInt,
UUID.randomUUID().toString());
}
});
thread.setName("Update Thread "+i);
updateThreads.add(thread);
thread.start();
}
How It Works
For performing work on a HashTable in a concurrent manner, Concur-
rentHashMap allows multiple threads to modify the HashTable concurrently and
safely. ConcurrentHashMap is a HashTable supporting full concurrency for re-
trievals, and high concurrency for updates. In the example, 1,000 threads make modi-
fications to the Map over a short period of time. The ConcurrentHashMap iterator,
as well as streams that are generated on a ConcurrentHashMap , allows safe itera-
tion over its contents. When using the ConcurrentMap 's iterator, you do not have to
worry about locking the contents of the ConcurrentMap while iterating over it (and
it doesn't throw ConcurrentModificationExceptions ).
For a complete list of the newly added methods, refer to the online documentation
at http://docs.oracle.com/javase/8/docs/api/java/util/con-
current/ConcurrentHashMap.html .
Note ConcurrentMap iterators, while thread-safe, don't guarantee that you will
see entries added/updated after the iterator was created.