Java 类java.util.concurrent.ThreadPoolExecutor.DiscardOldestPolicy 实例源码

/**
 * executor using DiscardOldestPolicy drops oldest task if saturated.
 */
public void testSaturatedExecute_DiscardOldestPolicy() {
    final CountDownLatch done = new CountDownLatch(1);
    LatchAwaiter r1 = awaiter(done);
    LatchAwaiter r2 = awaiter(done);
    LatchAwaiter r3 = awaiter(done);
    final ThreadPoolExecutor p =
        new ThreadPoolExecutor(1, 1,
                               LONG_DELAY_MS, MILLISECONDS,
                               new ArrayBlockingQueue<Runnable>(1),
                               new DiscardOldestPolicy());
    try (PoolCleaner cleaner = cleaner(p, done)) {
        assertEquals(LatchAwaiter.NEW, r1.state);
        assertEquals(LatchAwaiter.NEW, r2.state);
        assertEquals(LatchAwaiter.NEW, r3.state);
        p.execute(r1);
        p.execute(r2);
        assertTrue(p.getQueue().contains(r2));
        p.execute(r3);
        assertFalse(p.getQueue().contains(r2));
        assertTrue(p.getQueue().contains(r3));
    }
    assertEquals(LatchAwaiter.DONE, r1.state);
    assertEquals(LatchAwaiter.NEW, r2.state);
    assertEquals(LatchAwaiter.DONE, r3.state);
}

/**
 * execute using DiscardOldestPolicy drops task on shutdown
 */
public void testDiscardOldestOnShutdown() {
    final ThreadPoolExecutor p =
        new ThreadPoolExecutor(1, 1,
                               LONG_DELAY_MS, MILLISECONDS,
                               new ArrayBlockingQueue<Runnable>(1),
                               new DiscardOldestPolicy());

    try { p.shutdown(); } catch (SecurityException ok) { return; }
    try (PoolCleaner cleaner = cleaner(p)) {
        TrackedNoOpRunnable r = new TrackedNoOpRunnable();
        p.execute(r);
        assertFalse(r.done);
    }
}

@Override
RejectedExecutionHandler getHandler() {
    return new ThreadPoolExecutor.DiscardOldestPolicy();
}