Examples of ZkSemaphore

org.menagerie.latches.spi.ZkSemaphore
A ZooKeeper-based implementation of a fair counting Semaphore.
A {@code Semaphore} is a mechanism for allowing a limited number of parties to proceed at any given point in time.To facilitate this, conceptually, a Semaphore maintains a limited number of permits, which it grants to each party which calls {@link #acquire()} in sequence. Once a permit has been granted to a party, that party may proceed withits action, and when that action has finished, the party must return its permit via a call to {@link #release()}before another party may be granted that permit.
If no permits are available when a party makes its request, then it is either turned away (if the party calls {@link #tryAcquire()}) or made to wait via blocking (if the party calls {@link #acquire()}).
This implementation is conceptually similar to that of {@link java.util.concurrent.Semaphore}, but is distributed and fault-tolerant. If a party acquires a permit, and then subsequently fails, that permit is released back to the Semaphore, allowing another party to proceed.
Note that, due to the distributed nature of this semaphore, there are no guarantees that all semaphores in a cluster are required to see the same number of available permits. This makes it possible for a semaphore on Node A to allow, say, three parties access while the same semaphore on Node B allows 5 parties access. Instead, maintaining consistency as to the number of parties which are allowed through each semaphore is the responsibility of the calling code. @author Scott Fines @version 1.1 @see java.util.concurrent.Semaphore

Examples of org.menagerie.latches.spi.ZkSemaphore

    public final static DistributedCyclicBarrier newCyclicBarrier(long size, ZkSessionManager zkSessionManager, String barrierNode, List<ACL> privileges, boolean tolerateFailures) {
        return new ZkCyclicBarrier(size, zkSessionManager, barrierNode, privileges, tolerateFailures);
    }


    public final static DistributedSemaphore newSemaphore(int numPermits, String baseNode, ZkSessionManager zkSessionManager, List<ACL> privileges) {
        return new ZkSemaphore(numPermits, baseNode, zkSessionManager, privileges);
    }

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Examples of org.menagerie.latches.spi.ZkSemaphore

    public final static DistributedSemaphore newSemaphore(int numPermits, String baseNode, ZkSessionManager zkSessionManager, List<ACL> privileges) {
        return new ZkSemaphore(numPermits, baseNode, zkSessionManager, privileges);
    }


    public final static DistributedSemaphore newSemaphore(int numPermits, String baseNode, ZkSessionManager zkSessionManager) {
        return new ZkSemaphore(numPermits, baseNode, zkSessionManager);
    }

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Examples of org.menagerie.latches.spi.ZkSemaphore

    }


    @Test(timeout = 1000l)
    public void testAcquireSucceedsOneThread() throws Exception{
        int numPermits = 1;
        DistributedSemaphore semaphore = new ZkSemaphore(numPermits, basePath,zkSessionManager);


        semaphore.acquire();


        //check that the available permits are zero
        assertEquals("semaphore does not report fewer permits!",numPermits-1,semaphore.availablePermits());
        semaphore.release();
        assertEquals("semaphore does not report releasing a permit!",numPermits,semaphore.availablePermits());
    }

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Examples of org.menagerie.latches.spi.ZkSemaphore

    }


    @Test(timeout = 1000l)
    public void testTwoThreadsCanAccessSempahore() throws Exception{
        final CountDownLatch latch = new CountDownLatch(1);
        final DistributedSemaphore semaphore = new ZkSemaphore(2,basePath,zkSessionManager);


        testService.submit(new Runnable() {
            @Override
            public void run() {
                try {
                    semaphore.acquire();
                    latch.countDown();
                } catch (InterruptedException e) {
                    throw new RuntimeException(e);
                }
            }
        });


        semaphore.acquire();
        latch.await();
    }

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Examples of org.menagerie.latches.spi.ZkSemaphore

    }


    @Test(timeout = 1000l)
    public void testTwoClientsCanAccessSempahore() throws Exception{
        final CountDownLatch latch = new CountDownLatch(1);
        final DistributedSemaphore semaphore = new ZkSemaphore(2,basePath,zkSessionManager);


        semaphore.acquire();
        Future<Void> errorFuture = testService.submit(new Callable<Void>() {
            @Override
            public Void call() throws Exception {
                ZooKeeper zk = newZooKeeper();
                try {


                    DistributedSemaphore semaphore2 = new ZkSemaphore(2, basePath, new BaseZkSessionManager(zk));
                    semaphore2.acquire();
                    latch.countDown();
                } finally {
                    zk.close();
                }
                return null;

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Examples of org.menagerie.latches.spi.ZkSemaphore




    @Test(timeout = 1500l)
    public void testRunOutOfPermitsTwoThreads() throws Exception{
        final CountDownLatch latch = new CountDownLatch(1);
        final DistributedSemaphore semaphore = new ZkSemaphore(1,basePath,zkSessionManager);
        semaphore.acquire();
        Future<?> errorFuture = testService.submit(new Runnable() {
            @Override
            public void run() {
                try {
                    semaphore.acquire();
                    latch.countDown();
                } catch (InterruptedException e) {
                    throw new RuntimeException(e);
                }
            }
        });


        boolean timedOut = !latch.await(500, TimeUnit.MILLISECONDS);
        assertTrue("Semaphore improperly acquired a permit!",timedOut);


        semaphore.release();
        boolean noTimeOut = latch.await(500, TimeUnit.MILLISECONDS);
        assertTrue("Semaphore did not release a permit for another party!",noTimeOut);
        errorFuture.get();
    }

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Examples of org.menagerie.latches.spi.ZkSemaphore

    }


    @Test(timeout = 1500l)
    public void testRunOutOfPermitsTwoClients() throws Exception{
        final CountDownLatch latch = new CountDownLatch(1);
        final DistributedSemaphore semaphore = new ZkSemaphore(1,basePath,zkSessionManager);
        semaphore.acquire();
        Future<Void> errorFuture = testService.submit(new Callable<Void>() {
            @Override
            public Void call() throws Exception {
                ZooKeeper zk = newZooKeeper();
                try {
                    DistributedSemaphore semaphore2 = new ZkSemaphore(1, basePath, new BaseZkSessionManager(zk));
                    semaphore2.acquire();
                    latch.countDown();
                } finally {
                    zk.close();
                }
                return null;

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Examples of org.menagerie.latches.spi.ZkSemaphore

        errorFuture.get();
    }


    @Test(timeout = 1000l)
    public void testAcquireMultiplePermits() throws Exception{
        DistributedSemaphore semaphore = new ZkSemaphore(2,basePath,zkSessionManager);


        semaphore.acquire(2);
        assertEquals("Incorrect number of permits reported!",0,semaphore.availablePermits());


        semaphore.release();
        assertEquals("Incorrect number of permits reported",1,semaphore.availablePermits());


        semaphore.release();
        assertEquals("Incorrect number of permits reported",2,semaphore.availablePermits());
    }

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Examples of org.menagerie.latches.spi.ZkSemaphore

    }


    @Test(timeout = 2000l)
    public void testAcquireMultiplePermitsBlocksUntilAvailableTwoThreads() throws Exception{
        final CountDownLatch latch = new CountDownLatch(1);
        final DistributedSemaphore semaphore = new ZkSemaphore(2,basePath,zkSessionManager);


        semaphore.acquire(2);
        assertEquals("Incorrect number of permits reported!",0,semaphore.availablePermits());
        Future<Void> errorFuture = testService.submit(new Callable<Void>() {
            @Override
            public Void call() throws Exception {
                semaphore.acquire(2);
                latch.countDown();
                return null;
            }
        });


        boolean timedOut1 = !latch.await(500, TimeUnit.MILLISECONDS);
        assertTrue("multiple permits were incorrectly acquired",timedOut1);
        semaphore.release();


        boolean timedOut2 = !latch.await(500, TimeUnit.MILLISECONDS);
        assertTrue("multiple permits were incorrectly acquired",timedOut2);


        semaphore.release();
        boolean timedOut3 = latch.await(500,TimeUnit.MILLISECONDS);
        assertTrue("multiple permits were incorrectly released",timedOut3);
        errorFuture.get();
    }

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Examples of org.menagerie.latches.spi.ZkSemaphore

    }


    @Test(timeout = 2000l)
    public void testAcquireMultiplePermitsBlocksUntilAvailableTwoClients() throws Exception{
        final CountDownLatch latch = new CountDownLatch(1);
        final DistributedSemaphore semaphore = new ZkSemaphore(2,basePath,zkSessionManager);


        semaphore.acquire();
        semaphore.acquire();
        assertEquals("Incorrect number of permits reported!",0,semaphore.availablePermits());
        Future<Void> errorFuture = testService.submit(new Callable<Void>() {
            @Override
            public Void call() throws Exception {
                ZooKeeper zk = newZooKeeper();
                try {
                    DistributedSemaphore semaphore2 = new ZkSemaphore(2, basePath, new BaseZkSessionManager(zk));
                    semaphore2.acquire(2);
                    latch.countDown();
                } finally {
                    zk.close();
                }
                return null;

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