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import java.util.concurrent.TimeUnit;
import java.util.concurrent.Phaser;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.atomic.AtomicInteger;
import java.util.concurrent.atomic.AtomicReference;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.ReentrantLock;
import java.util.function.Consumer;
import java.util.stream.IntStream;
import java.util.stream.Stream;

/**
 * @test
 * @bug 8066859
 * @summary Check that AQS-based locks, conditions, and CountDownLatches do not fail when encountering OOME
 * @requires vm.gc.G1
 * @run main/othervm -XX:+UseG1GC -XX:-UseGCOverheadLimit -Xmx48M -XX:-UseTLAB OOMEInAQS
 */

public class OOMEInAQS extends Thread {
    static final int NTHREADS = 2; // intentionally not a scalable test; > 2 is very slow
    static final int NREPS = 100;
    // statically allocate
    static final ReentrantLock mainLock = new ReentrantLock();
    static final Condition condition = mainLock.newCondition();
    static final CountDownLatch started = new CountDownLatch(1);
    static final CountDownLatch filled = new CountDownLatch(1);
    static final CountDownLatch canFill = new CountDownLatch(NTHREADS);
    static volatile Object data;
    static volatile Throwable exception;
    static int turn;

    /**
     * For each of NTHREADS threads, REPS times: Take turns
     * executing. Introduce OOM using fillHeap during runs. In
     * addition to testing AQS, the CountDownLatches ensure that
     * methods execute at least once before OutOfMemory occurs, to
     * avoid uncontrollable impact of OOME during class-loading.
     */
    public static void main(String[] args) throws Throwable {
        OOMEInAQS[] threads = new OOMEInAQS[NTHREADS];
        for (int i = 0; i < NTHREADS; ++i)
            (threads[i] = new OOMEInAQS(i)).start();
        started.countDown();
        canFill.await();
        long t0 = System.nanoTime();
        data = fillHeap();
        filled.countDown();
        long t1 = System.nanoTime();
        for (int i = 0; i < NTHREADS; ++i)
            threads[i].join();
        data = null;  // free heap before reporting and terminating
        System.gc();
        Throwable ex = exception;
        if (ex != null)
            throw ex;
        System.out.println(
            "fillHeap time: " + (t1 - t0) / 1000_000 +
            " millis, whole test time: " + (System.nanoTime() - t0) / 1000_000 +
            " millis"
        );
    }

    final int tid;
    OOMEInAQS(int tid) {
        this.tid = tid;
    }

    @Override
    public void run() {
        int id = tid, nextId = (id + 1) % NTHREADS;
        final ReentrantLock lock = mainLock;
        final Condition cond = condition;
        try {
            started.await();
            for (int i = 0; i < NREPS; i++) {
                lock.lock();
                try {
                    while (turn != id)
                        cond.await();
                    turn = nextId;
                    cond.signalAll();
                } finally {
                    lock.unlock();
                }
                if (i == 2) {  // Subsequent AQS methods encounter OOME
                    canFill.countDown();
                    filled.await();
                }
            }
            data = null;
            System.gc(); // avoid getting stuck while exiting
        } catch (Throwable ex) {
            data = null;
            System.gc(); // avoid nested OOME
            exception = ex;
        }
    }

    static Object[] fillHeap() {
        Object[] first = null, last = null;
        int size = 1 << 20;
        while (size > 0) {
            try {
                Object[] array = new Object[size];
                if (first == null) {
                    first = array;
                } else {
                    last[0] = array;
                }
                last = array;
            } catch (OutOfMemoryError oome) {
                size = size >>> 1;
            }
        }
        return first;
    }
}