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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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 * 2 along with this work; if not, write to the Free Software Foundation,
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/*
 * @test
 * @bug 4486658 8010293
 * @summary thread safety of toArray methods of subCollections
 * @author Martin Buchholz
 */

import java.util.concurrent.CompletableFuture;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.stream.IntStream;

public class ToArray {

    public static void main(String[] args) throws Throwable {
        // Execute a number of times to increase the probability of
        // failure if there is an issue
        for (int i = 0; i < 16; i++) {
            executeTest();
        }
    }

    static void executeTest() throws Throwable {
        ExecutorService executor = Executors.newCachedThreadPool();
        try {
            final Throwable[] throwable = new Throwable[1];
            final ConcurrentHashMap<Integer, Integer> m = new ConcurrentHashMap<>();

            // Number of workers equal to the number of processors
            // Each worker will put globally unique keys into the map
            final int nWorkers = Runtime.getRuntime().availableProcessors();
            final int sizePerWorker = 1024;
            final int maxSize = nWorkers * sizePerWorker;

            // The foreman keeps checking that the size of the arrays
            // obtained from the key and value sets is never less than the
            // previously observed size and is never greater than the maximum size
            // NOTE: these size constraints are not specific to toArray and are
            // applicable to any form of traversal of the collection views
            CompletableFuture<?> foreman = CompletableFuture.runAsync(new Runnable() {
                private int prevSize = 0;

                private boolean checkProgress(Object[] a) {
                    int size = a.length;
                    if (size < prevSize) throw new RuntimeException("WRONG WAY");
                    if (size > maxSize) throw new RuntimeException("OVERSHOOT");
                    if (size == maxSize) return true;
                    prevSize = size;
                    return false;
                }

                @Override
                public void run() {
                    try {
                        Integer[] empty = new Integer[0];
                        while (true) {
                            if (checkProgress(m.values().toArray())) return;
                            if (checkProgress(m.keySet().toArray())) return;
                            if (checkProgress(m.values().toArray(empty))) return;
                            if (checkProgress(m.keySet().toArray(empty))) return;
                        }
                    } catch (Throwable t) {
                        throwable[0] = t;
                    }
                }
            }, executor);

            // Create workers
            // Each worker will put globally unique keys into the map
            CompletableFuture<?>[] workers = IntStream.range(0, nWorkers).
                    mapToObj(w -> CompletableFuture.runAsync(() -> {
                        for (int i = 0, o = w * sizePerWorker; i < sizePerWorker; i++)
                            m.put(o + i, i);
                    }, executor)).
                    toArray(CompletableFuture<?>[]::new);

            // Wait for workers and then foreman to complete
            CompletableFuture.allOf(workers).join();
            foreman.join();

            if (throwable[0] != null)
                throw throwable[0];
        } finally {
            executor.shutdownNow();
        }
    }
}