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.

        assertEquals(6, s.availablePermits());
    }


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


        getClient().send(new ReleaseRequest(name, 4));
        boolean result = (Boolean) getClient().receive();
        assertTrue(result);
        assertEquals(14, s.availablePermits());
    }

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        hz = createHazelcastInstance();
    }


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


        int numberOfPermits = 20;
        assertTrue(semaphore.init(numberOfPermits));
        for (int i = 0; i < numberOfPermits; i++) {
            assertEquals(numberOfPermits - i, semaphore.availablePermits());
            semaphore.acquire();
        }


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

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


    @Test(timeout = 30000)
    public void testAcquire_whenNoPermits() throws InterruptedException {
        final ISemaphore semaphore = hz.getSemaphore(randomString());
        semaphore.init(0);
        final AcquireThread acquireThread = new AcquireThread(semaphore);
        acquireThread.start();
        assertTrueAllTheTime(new AssertTask() {
            @Override
            public void run() throws Exception {
                assertTrue(acquireThread.isAlive());
                assertEquals(0, semaphore.availablePermits());
            }
        }, 5);
    }

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        }, 5);
    }


    @Test(timeout = 30000)
    public void testAcquire_whenNoPermits_andSemaphoreDestroyed() throws InterruptedException {
        final ISemaphore semaphore = hz.getSemaphore(randomString());
        AcquireThread thread = new AcquireThread(semaphore);
        thread.start();


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

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


    @Test(expected = IllegalStateException.class, timeout = 30000)
    public void testAcquire_whenInstanceShutdown() throws InterruptedException {
        final ISemaphore semaphore = hz.getSemaphore(randomString());
        hz.shutdown();
        semaphore.acquire();
    }

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        semaphore.acquire();
    }


    @Test(timeout = 30000)
    public void testRelease() {
        final ISemaphore semaphore = hz.getSemaphore(randomString());


        int numberOfPermits = 20;
        for (int i = 0; i < numberOfPermits; i++) {
            assertEquals(i, semaphore.availablePermits());
            semaphore.release();
        }


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

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


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

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


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


        new Thread() {
            @Override
            public void run() {
                try {
                    semaphore.acquire();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        }.start();
        semaphore.release();


        assertTrueEventually(new AssertTask() {
            @Override
            public void run() throws Exception {
                assertEquals(0, semaphore.availablePermits());
            }
        });
    }

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        });
    }


    @Test(timeout = 30000)
    public void testMultipleAcquire() throws InterruptedException {
        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.acquire(5);
        }
        assertEquals(semaphore.availablePermits(), 0);
    }

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


    @Test(timeout = 30000)
    public void testMultipleAcquire_whenNegative() throws InterruptedException {
        final ISemaphore semaphore = hz.getSemaphore(randomString());
        int numberOfPermits = 10;
        semaphore.init(numberOfPermits);
        try {
            for (int i = 0; i < numberOfPermits; i += 5) {
                semaphore.acquire(-5);
                fail();
            }
        } catch (IllegalArgumentException expected) {
        }
        assertEquals(10, semaphore.availablePermits());


    }

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