test/java/lang/ref/ReferenceEnqueuePending.java

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/* @test
 * @bug 4243978
 * @summary Test if Reference.enqueue() works properly with pending references
 */
import java.lang.ref.*;

public class ReferenceEnqueuePending {
    static class NumberedWeakReference extends WeakReference<Integer> {
        //  Add an integer to identify the weak reference object.
        int number;

        NumberedWeakReference(Integer referent, ReferenceQueue<Integer> q, int i) {
            super(referent, q);
            number = i;
        }
    }

    final static boolean debug = System.getProperty("test.debug") != null;
    final static int iterations = 1000;
    final static int gc_trigger = 99;
    static int[] a = new int[2 * iterations];
    // Keep all weak references alive with the following array.
    static NumberedWeakReference[] b = new NumberedWeakReference[iterations];

    public static void main(String[] argv) throws Exception {
        if (debug) {
            System.out.println("Starting the test.");
        }
        // Raise thread priority to match the referenceHandler
        // priority, so that they can race also on a uniprocessor.
        raisePriority();

        ReferenceQueue<Integer> refQueue = new ReferenceQueue<>();

        // Our objective is to let the mutator enqueue
        // a Reference object that may already be in the
        // pending state because of having been identified
        // as weakly reachable at a previous garbage collection.
        // To this end, we create many Reference objects, each with a
        // a unique integer object as its referant.
        // We let the referents become eligible for collection,
        // while racing with the garbage collector which may
        // have pended some of these Reference objects.
        // Finally we check that all of the Reference objects
        // end up on the their queue. The test was originally
        // submitted to show that such races could break the
        // pending list and/or the reference queue, because of sharing
        // the same link ("next") for maintaining both lists, thus
        // losing some of the Reference objects on either queue.

        Integer obj = new Integer(0);
        NumberedWeakReference weaky = new NumberedWeakReference(obj, refQueue, 0);
        for (int i = 1; i < iterations; i++) {
            // Create a new object, dropping the onlY strong reference to
            // the previous Integer object.
            obj = new Integer(i);
            // Trigger gc each gc_trigger iterations.
            if ((i % gc_trigger) == 0) {
                forceGc(0);
            }
            // Enqueue every other weaky.
            if ((i % 2) == 0) {
                weaky.enqueue();
            }
            // Remember the Reference objects, for testing later.
            b[i - 1] = weaky;
            // Get a new weaky for the Integer object just
            // created, which may be explicitly enqueued in
            // our next trip around the loop.
            weaky = new NumberedWeakReference(obj, refQueue, i);
        }

        // Do a final collection to discover and process all
        // Reference objects created above, allowing enough time
        // for the ReferenceHandler thread to queue the References.
        forceGc(100);
        forceGc(100);

        // Verify that all WeakReference objects ended up queued.
        checkResult(refQueue, obj, iterations-1);
        System.out.println("Test passed.");
    }

    private static void checkResult(ReferenceQueue<Integer> queue,
                                    Integer obj,
                                    int expected) {
        if (debug) {
            System.out.println("Reading the queue");
        }

        // Empty the queue and record numbers into a[];
        NumberedWeakReference weakRead = (NumberedWeakReference) queue.poll();
        int length = 0;
        while (weakRead != null) {
            a[length++] = weakRead.number;
            weakRead = (NumberedWeakReference) queue.poll();
        }
        if (debug) {
            System.out.println("Reference Queue had " + length + " elements");
        }
        // Use the last Reference object of those created above, so as to keep it "alive".
        System.out.println("I must write " + obj + " to prevent compiler optimizations.");


        // verify the queued references: all but the last Reference object
        // should have been in the queue.
        if (debug) {
            System.out.println("Start of final check");
        }

        // Sort the first "length" elements in array "a[]".
        sort(length);

        boolean fail = (length != expected);
        for (int i = 0; i < length; i++) {
            if (a[i] != i) {
                if (debug) {
                    System.out.println("a[" + i + "] is not " + i + " but " + a[i]);
                }
                fail = true;
            }
        }
        if (fail) {
             printMissingElements(length, expected);
             throw new RuntimeException("TEST FAILED: only " + length
                    + " reference objects have been queued out of "
                    + expected);
        }
    }

    private static void printMissingElements(int length, int expected) {
        System.out.println("The following numbers were not found in the reference queue: ");
        int missing = 0;
        int element = 0;
        for (int i = 0; i < length; i++) {
            while ((a[i] != element) & (element < expected)) {
                System.out.print(element + " ");
                if (missing % 20 == 19) {
                    System.out.println(" ");
                }
                missing++;
                element++;
            }
            element++;
        }
        System.out.print("\n");
    }

    private static void forceGc(long millis) throws InterruptedException {
        Runtime.getRuntime().gc();
        Thread.sleep(millis);
    }

    // Bubble sort the first "length" elements in array "a".
    private static void sort(int length) {
        int hold;
        if (debug) {
            System.out.println("Sorting. Length=" + length);
        }
        for (int pass = 1; pass < length; pass++) {    // passes over the array
            for (int i = 0; i < length - pass; i++) {  //  a single pass
                if (a[i] > a[i + 1]) {  // then swap
                    hold = a[i];
                    a[i] = a[i + 1];
                    a[i + 1] = hold;
                }
            }  // End of i loop
        } // End of pass loop
    }

    // Raise thread priority so as to increase the
    // probability of the mutator succeeding in enqueueing
    // an object that is still in the pending state.
    // This is (probably) only required for a uniprocessor.
    static void raisePriority() {
        Thread tr = Thread.currentThread();
        tr.setPriority(Thread.MAX_PRIORITY);
    }
}   // End of class ReferenceEnqueuePending