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 = 30000)
    public void testMultipleAcquire_whenNotEnoughPermits() throws InterruptedException {
        final ISemaphore semaphore = hz.getSemaphore(randomString());
        int numberOfPermits = 5;
        semaphore.init(numberOfPermits);
        final Thread thread = new Thread() {
            @Override
            public void run() {
                try {
                    semaphore.acquire(6);
                    assertEquals(5, semaphore.availablePermits());
                    semaphore.acquire(6);
                    assertEquals(5, semaphore.availablePermits());
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        };
        thread.start();


        assertTrueAllTheTime(new AssertTask() {
            @Override
            public void run() throws Exception {
                assertTrue(thread.isAlive());
                assertEquals(5, semaphore.availablePermits());
            }
        }, 5);
    }

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        }, 5);
    }


    @Test(timeout = 30000)
    public void testMultipleRelease() {
        final ISemaphore semaphore = hz.getSemaphore(randomString());
        int numberOfPermits = 20;


        for (int i = 0; i < numberOfPermits; i += 5) {
            assertEquals(i, semaphore.availablePermits());
            semaphore.release(5);
        }
        assertEquals(semaphore.availablePermits(), numberOfPermits);
    }

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        assertEquals(semaphore.availablePermits(), numberOfPermits);
    }


    @Test(timeout = 30000)
    public void testMultipleRelease_whenNegative() throws InterruptedException {
        final ISemaphore semaphore = hz.getSemaphore(randomString());
        semaphore.init(0);


        try {
            semaphore.release(-5);
            fail();


        } catch (IllegalArgumentException expected) {
        }
        assertEquals(0, semaphore.availablePermits());
    }

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    }


    @Repeat(10)
    @Test(timeout = 30000)
    public void testMultipleRelease_whenBlockedAcquireThreads() throws InterruptedException {
        final ISemaphore semaphore = hz.getSemaphore(randomString());
        int numberOfPermits = 10;
        semaphore.init(numberOfPermits);
        semaphore.acquire(numberOfPermits);
        CountDownLatch latch1 = new CountDownLatch(1);
        Thread thread1 = new BlockAcquireThread(semaphore, latch1);
        thread1.start();


        semaphore.release();
        assertOpenEventually(latch1);
    }

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        assertOpenEventually(latch1);
    }


    @Test(timeout = 30000)
    public void testDrain() throws InterruptedException {
        final ISemaphore semaphore = hz.getSemaphore(randomString());
        int numberOfPermits = 20;


        assertTrue(semaphore.init(numberOfPermits));
        semaphore.acquire(5);
        int drainedPermits = semaphore.drainPermits();
        assertEquals(drainedPermits, numberOfPermits - 5);
        assertEquals(semaphore.availablePermits(), 0);
    }

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


    @Test(timeout = 30000)
    public void testDrain_whenNoPermits() throws InterruptedException {
        final ISemaphore semaphore = hz.getSemaphore(randomString());
        semaphore.init(0);
        assertEquals(0, semaphore.drainPermits());
    }

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        assertEquals(0, semaphore.drainPermits());
    }


    @Test(timeout = 30000)
    public void testReduce() {
        final ISemaphore semaphore = hz.getSemaphore(randomString());
        int numberOfPermits = 20;


        assertTrue(semaphore.init(numberOfPermits));
        for (int i = 0; i < numberOfPermits; i += 5) {
            assertEquals(numberOfPermits - i, semaphore.availablePermits());
            semaphore.reducePermits(5);
        }


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

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


    @Test(timeout = 30000)
    public void testReduce_whenArgumentNegative() {
        final ISemaphore semaphore = hz.getSemaphore(randomString());
        try {
            semaphore.reducePermits(-5);
            fail();
        } catch (IllegalArgumentException expected) {
        }
        assertEquals(0, semaphore.availablePermits());
    }

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    }




    @Test(timeout = 30000)
    public void testTryAcquire() {
        final ISemaphore semaphore = hz.getSemaphore(randomMapName());
        int numberOfPermits = 20;


        assertTrue(semaphore.init(numberOfPermits));
        for (int i = 0; i < numberOfPermits; i++) {
            assertEquals(numberOfPermits - i, semaphore.availablePermits());
            assertEquals(semaphore.tryAcquire(), true);
        }
        assertFalse(semaphore.tryAcquire());
        assertEquals(semaphore.availablePermits(), 0);
    }

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


    @Test(timeout = 30000)
    public void testTryAcquireMultiple() {
        final ISemaphore semaphore = hz.getSemaphore(randomString());
        int numberOfPermits = 20;


        assertTrue(semaphore.init(numberOfPermits));
        for (int i = 0; i < numberOfPermits; i += 5) {
            assertEquals(numberOfPermits - i, semaphore.availablePermits());
            assertEquals(semaphore.tryAcquire(5), true);
        }


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

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