org.apache.kafka.streams.processor.internals.assignment.ConstrainedPrioritySet Maven / Gradle / Ivy
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* (the "License"); you may not use this file except in compliance with
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* http://www.apache.org/licenses/LICENSE-2.0
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package org.apache.kafka.streams.processor.internals.assignment;
import org.apache.kafka.streams.processor.TaskId;
import java.util.Collection;
import java.util.Comparator;
import java.util.HashSet;
import java.util.PriorityQueue;
import java.util.Set;
import java.util.UUID;
import java.util.function.BiFunction;
import java.util.function.Function;
/**
* Wraps a priority queue of clients and returns the next valid candidate(s) based on the current task assignment
*/
class ConstrainedPrioritySet {
private final PriorityQueue clientsByTaskLoad;
private final BiFunction constraint;
private final Set uniqueClients = new HashSet<>();
ConstrainedPrioritySet(final BiFunction constraint,
final Function weight) {
this.constraint = constraint;
clientsByTaskLoad = new PriorityQueue<>(Comparator.comparing(weight).thenComparing(clientId -> clientId));
}
/**
* @return the next least loaded client that satisfies the given criteria, or null if none do
*/
UUID poll(final TaskId task, final Function extraConstraint) {
final Set invalidPolledClients = new HashSet<>();
while (!clientsByTaskLoad.isEmpty()) {
final UUID candidateClient = pollNextClient();
if (constraint.apply(candidateClient, task) && extraConstraint.apply(candidateClient)) {
// then we found the lightest, valid client
offerAll(invalidPolledClients);
return candidateClient;
} else {
// remember this client and try again later
invalidPolledClients.add(candidateClient);
}
}
// we tried all the clients, and none met the constraint (or there are no clients)
offerAll(invalidPolledClients);
return null;
}
/**
* @return the next least loaded client that satisfies the given criteria, or null if none do
*/
UUID poll(final TaskId task) {
return poll(task, client -> true);
}
void offerAll(final Collection clients) {
for (final UUID client : clients) {
offer(client);
}
}
void offer(final UUID client) {
if (uniqueClients.contains(client)) {
clientsByTaskLoad.remove(client);
} else {
uniqueClients.add(client);
}
clientsByTaskLoad.offer(client);
}
private UUID pollNextClient() {
final UUID client = clientsByTaskLoad.remove();
uniqueClients.remove(client);
return client;
}
}