dcapwell commented on code in PR #3073: URL: https://github.com/apache/cassandra/pull/3073#discussion_r1478668664
########## src/java/org/apache/cassandra/repair/Scheduler.java: ########## @@ -0,0 +1,181 @@ +/* + * Licensed to the Apache Software Foundation (ASF) under one + * or more contributor license agreements. See the NOTICE file + * distributed with this work for additional information + * regarding copyright ownership. The ASF licenses this file + * to you under the Apache License, Version 2.0 (the + * "License"); you may not use this file except in compliance + * with the License. You may obtain a copy of the License at + * + * http://www.apache.org/licenses/LICENSE-2.0 + * + * Unless required by applicable law or agreed to in writing, software + * distributed under the License is distributed on an "AS IS" BASIS, + * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. + * See the License for the specific language governing permissions and + * limitations under the License. + */ + +package org.apache.cassandra.repair; + +import java.util.ArrayList; +import java.util.HashMap; +import java.util.List; +import java.util.Map; +import java.util.concurrent.Executor; +import java.util.concurrent.TimeUnit; +import javax.annotation.concurrent.GuardedBy; + +import org.agrona.collections.LongArrayList; +import org.apache.cassandra.utils.TimeUUID; +import org.apache.cassandra.utils.concurrent.AsyncFuture; + +public interface Scheduler +{ + void schedule(TimeUUID sessionId, Executor taskExecutor, Task<?> tasks); + + static Scheduler build(int concurrentValidations, SharedContext ctx) + { + return concurrentValidations <= 0 + ? new NoopScheduler() + : new LimitedConcurrentScheduler(concurrentValidations, ctx); + } + + final class NoopScheduler implements Scheduler + { + @Override + public void schedule(TimeUUID sessionId, Executor taskExecutor, Task<?> tasks) + { + taskExecutor.execute(tasks); + } + } + + final class LimitedConcurrentScheduler implements Scheduler + { + private final int concurrentValidations; + private final SharedContext ctx; + @GuardedBy("this") + private int inflight = 0; + @GuardedBy("this") + private final Map<TimeUUID, Group> groups = new HashMap<>(); + + LimitedConcurrentScheduler(int concurrentValidations, SharedContext ctx) + { + this.concurrentValidations = concurrentValidations; + this.ctx = ctx; + } + + @Override + public synchronized void schedule(TimeUUID sessionId, Executor taskExecutor, Task<?> tasks) + { + groups.computeIfAbsent(sessionId, ignore -> new Group(sessionId, taskExecutor)).add(tasks); + maybeSchedule(); + } + + private synchronized void onDone(Group group, long durationNs) + { + group.update(durationNs); + inflight--; + maybeSchedule(); + } + + private void maybeSchedule() + { + if (inflight == concurrentValidations) + return; + Group smallest = null; + long smallestScore = -1; + for (var g : groups.values()) + { + if (g.isEmpty()) + continue; + if (smallest == null) + { + smallest = g; + smallestScore = g.score(); + } + else + { + var score = g.score(); + if (score < smallestScore) + { + smallest = g; + smallestScore = score; + } + } + } + if (smallest == null) + return; + inflight++; + smallest.executeNext(); + } + + private class Group + { + private final TimeUUID sessionId; + private final Executor taskExecutor; + private final List<Task<?>> tasks = new ArrayList<>(); + private final LongArrayList durations = new LongArrayList(); + private int inflight = 0; + private int completed = 0; + + private Group(TimeUUID sessionId, Executor taskExecutor) + { + this.sessionId = sessionId; + this.taskExecutor = taskExecutor; + } + + public long score() + { + if (tasks.isEmpty()) + return -1; + long avgDuration = (long) durations.longStream().average().orElse(TimeUnit.HOURS.toNanos(1)); + return tasks.size() * avgDuration; + } + + public void executeNext() + { + Task<?> task = tasks.get(0); + tasks.remove(0); + inflight++; + var startNs = ctx.clock().nanoTime(); + task.addCallback((s, f) -> onDone(this, ctx.clock().nanoTime() - startNs)); + taskExecutor.execute(task); + } + + public void add(Task<?> task) + { + tasks.add(task); + } + + private void update(long durationNs) + { + durations.add(durationNs); + inflight--; + completed++; + } + + public boolean isEmpty() + { + return tasks.isEmpty(); + } + + @Override + public String toString() + { + return "Group{" + + "sessionId=" + sessionId + + ", tasks=" + tasks.size() + + ", durations=" + durations.longStream().average().orElse(-1) + + ", score=" + score() + + ", inflight=" + inflight + + ", completed=" + completed + + '}'; + } + } + } + + abstract class Task<T> extends AsyncFuture<T> implements Runnable Review Comment: isn't this just `org.apache.cassandra.concurrent.FutureTask`? -- This is an automated message from the Apache Git Service. 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