Examples of com.hazelcast.core.ISemaphore

com.hazelcast.core.ISemaphore
ISemaphore is a backed-up distributed alternative to the {@link java.util.concurrent.Semaphore}.
ISemaphore is a cluster-wide counting semaphore. Conceptually, it maintains a set of permits. Each {@link #acquire()} blocks if necessary untila permit is available, and then takes it. Each {@link #release()} adds a permit,potentially releasing a blocking acquirer. However, no actual permit objects are used; the semaphore just keeps a count of the number available and acts accordingly.
The Hazelcast distributed semaphore implementation guarantees that threads invoking any of the {@link #acquire() acquire} methods are selectedto obtain permits in the order in which their invocation of those methods was processed(first-in-first-out; FIFO). Note that FIFO ordering necessarily applies to specific internal points of execution within the cluster. So, it is possible for one member to invoke {@code acquire} before another, but reachthe ordering point after the other, and similarly upon return from the method.
This class also provides convenience methods to {@link #acquire(int) acquire} and {@link #release(int) release} multiplepermits at a time. Beware of the increased risk of indefinite postponement when using the multiple acquire. If a single permit is released to a semaphore that is currently blocking, a thread waiting for one permit will acquire it before a thread waiting for multiple permits regardless of the call order.
- Correct usage of a semaphore is established by programming convention in the application.

    @Test(timeout = 120000)
    public void testSemaphoreWithFailures() throws InterruptedException {
        final int k = 4;
        final TestHazelcastInstanceFactory factory = createHazelcastInstanceFactory(k + 1);
        final HazelcastInstance[] instances = factory.newInstances();
        final ISemaphore semaphore = instances[k].getSemaphore("test");
        int initialPermits = 20;


        semaphore.init(initialPermits);


        for (int i = 0; i < k; i++) {
            int rand = (int) (Math.random() * 5) + 1;


            semaphore.acquire(rand);
            initialPermits -= rand;
            assertEquals(initialPermits, semaphore.availablePermits());
            semaphore.release(rand);
            initialPermits += rand;
            assertEquals(initialPermits, semaphore.availablePermits());


            instances[i].shutdown();


            semaphore.acquire(rand);
            initialPermits -= rand;
            assertEquals(initialPermits, semaphore.availablePermits());
            semaphore.release(rand);
            initialPermits += rand;
            assertEquals(initialPermits, semaphore.availablePermits());
        }
    }

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    @Test(timeout = 120000)
    public void testSemaphoreWithFailuresAndJoin() {
        final TestHazelcastInstanceFactory factory = createHazelcastInstanceFactory(3);
        final HazelcastInstance instance1 = factory.newHazelcastInstance();
        final HazelcastInstance instance2 = factory.newHazelcastInstance();
        final ISemaphore semaphore = instance1.getSemaphore("test");
        final CountDownLatch countDownLatch = new CountDownLatch(1);


        assertTrue(semaphore.init(0));


        final Thread thread = new Thread() {
            public void run() {
                for (int i = 0; i < 2; i++) {
                    try {
                        semaphore.acquire();
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }
                countDownLatch.countDown();
            }
        };
        thread.start();


        instance2.shutdown();
        semaphore.release();


        HazelcastInstance instance3 = factory.newHazelcastInstance();
        ISemaphore semaphore1 = instance3.getSemaphore("test");
        semaphore1.release();


        try {
            assertTrue(countDownLatch.await(15, TimeUnit.SECONDS));
        } catch (InterruptedException e) {
            e.printStackTrace();

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        final Counter counter = new Counter();


        assertTrue(instances[0].getSemaphore("test").init(1));


        for (int i = 0; i < threadCount; i++) {
            final ISemaphore semaphore = instances[i].getSemaphore("test");
            new Thread() {
                public void run() {
                    for (int j = 0; j < loopCount; j++) {
                        try {
                            semaphore.acquire();
                            sleepMillis((int) (Math.random() * 3));
                            counter.inc();
                        } catch (InterruptedException e) {
                            return;
                        } finally {
                            semaphore.release();
                        }
                    }
                    latch.countDown();
                }
            }.start();

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        return new Config();
    }


    @Before
    public void start() throws IOException {
        ISemaphore s = getInstance().getSemaphore(name);
        s.reducePermits(100);
        assertEquals(0, s.availablePermits());
    }

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        assertEquals(0, s.availablePermits());
    }


    @After
    public void clear() throws IOException {
        ISemaphore s = getInstance().getSemaphore(name);
        s.reducePermits(100);
        assertEquals(0, s.availablePermits());
    }

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        assertEquals(0, s.availablePermits());
    }


    @Test
    public void testAcquire() throws Exception {
        ISemaphore s = getInstance().getSemaphore(name);
        assertTrue(s.init(10));


        getClient().send(new AcquireRequest(name, 3, 0));
        boolean result = (Boolean) getClient().receive();
        assertTrue(result);
        assertEquals(7, s.availablePermits());


        getClient().send(new AcquireRequest(name, 8, 6 * 1000));
        assertEquals(7, s.availablePermits());


        Thread.sleep(2 * 1000);


        s.release(1);


        result = (Boolean) getClient().receive();
        assertTrue(result);
        assertEquals(0, s.availablePermits());


        getClient().send(new AcquireRequest(name, 4, 2 * 1000));
        result = (Boolean) getClient().receive();
        assertFalse(result);

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    public void testAvailable() throws Exception {
        getClient().send(new AvailableRequest(name));
        int result = (Integer) getClient().receive();
        assertEquals(0, result);


        ISemaphore s = getInstance().getSemaphore(name);
        s.release(5);


        getClient().send(new AvailableRequest(name));
        result = (Integer) getClient().receive();
        assertEquals(5, result);
    }

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        assertEquals(5, result);
    }


    @Test
    public void testDrain() throws Exception {
        ISemaphore s = getInstance().getSemaphore(name);
        assertTrue(s.init(10));


        getClient().send(new DrainRequest(name));
        int result = (Integer) getClient().receive();
        assertEquals(10, result);


        s.release(4);


        getClient().send(new DrainRequest(name));
        result = (Integer) getClient().receive();
        assertEquals(4, result);
    }

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        assertEquals(4, result);
    }


    @Test
    public void testInit() throws Exception {
        ISemaphore s = getInstance().getSemaphore(name);


        getClient().send(new InitRequest(name, 10));
        boolean result = (Boolean) getClient().receive();
        assertTrue(result);
        assertEquals(10, s.availablePermits());


        getClient().send(new InitRequest(name, 20));
        result = (Boolean) getClient().receive();
        assertFalse(result);
        assertEquals(10, s.availablePermits());
    }

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        assertEquals(10, s.availablePermits());
    }


    @Test
    public void testReduce() throws Exception {
        ISemaphore s = getInstance().getSemaphore(name);
        assertTrue(s.init(10));


        getClient().send(new ReduceRequest(name, 4));
        boolean result = (Boolean) getClient().receive();
        assertTrue(result);
        assertEquals(6, s.availablePermits());
    }

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