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/*
 * (c) Copyright 2018 Palantir Technologies Inc. All rights reserved.
 *
 * Licensed 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 com.palantir.atlasdb.keyvalue.cassandra;

import com.google.common.util.concurrent.ListenableFuture;
import com.google.common.util.concurrent.ListeningExecutorService;
import com.google.common.util.concurrent.MoreExecutors;
import com.palantir.common.base.Throwables;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.concurrent.Callable;
import java.util.concurrent.ExecutorService;

class TaskRunner {
    private final ListeningExecutorService listeningExecutor;

    TaskRunner(ExecutorService executor) {
        this.listeningExecutor = MoreExecutors.listeningDecorator(executor);
    }

    /*
     * Similar to executor.invokeAll, but cancels all remaining tasks if one fails and doesn't spawn new threads if
     * there is only one task
     */
    @SuppressWarnings("MixedMutabilityReturnType") // Want to be immutable, but need to support null also
     List runAllTasksCancelOnFailure(List> tasks) {
        if (tasks.size() == 1) {
            try {
                // Callable returns null, so can't use immutable list
                return Collections.singletonList(tasks.get(0).call());
            } catch (Exception e) {
                throw Throwables.unwrapAndThrowAtlasDbDependencyException(e);
            }
        }

        List> futures = new ArrayList<>(tasks.size());
        for (Callable task : tasks) {
            futures.add(listeningExecutor.submit(task));
        }
        try {
            List results = new ArrayList<>(tasks.size());
            for (ListenableFuture future : futures) {
                results.add(future.get());
            }
            return results;
        } catch (Exception e) {
            throw Throwables.unwrapAndThrowAtlasDbDependencyException(e);
        } finally {
            for (ListenableFuture future : futures) {
                future.cancel(true);
            }
        }
    }
}