Re: Semaphore blocking on tryAcquire() while holding a cache-lock

[nyname00]

Yakov,

please see the code below. Simply start one node (in my case I started it
directly from eclipse using 1.8u45) and wait for a few cycles, then start up
the second node. You should see one more "sem created" message and then ...
silence. If you kill the first node, the code processes normal again - but
not when you kill the second one.

Also note that on the second node no "Topology snapshot" message appears
which, I guess, is not a good sign.

I'm still testing, but if you replace the "sched" map-lock with a semaphore,
everything seems to work ... until you kill one of the nodes. Then an
exception is thrown every time the worker tries to get a new semaphore.

Thanks for investigating,
Mario


public static void main(String[] args) {
        Ignite ignite = Ignition.start(new IgniteConfiguration());

        Lock lock = ignite
                .getOrCreateCache(
                        new CacheConfiguration<String,
Boolean>("sched").setAtomicityMode(TRANSACTIONAL))
                .lock("sched-lock");

        if (lock.tryLock()) {
            try {
                System.out.println("pre start sched");

                ScheduledExecutorService es =
Executors.newSingleThreadScheduledExecutor();
                ScheduledFuture<?> f = es.scheduleAtFixedRate(new 
Worker(ignite), 0, 2000,
TimeUnit.MILLISECONDS);

                System.out.println("post start sched");
                try {
                    f.get();
                } catch (Exception e) {
                    e.printStackTrace();
                } finally {
                    es.shutdownNow();
                }
            } finally {
                lock.unlock();
            }
        }
    }

    private static class Worker implements Runnable {
        private final Ignite ignite;

        public Worker(Ignite ignite) {
            this.ignite = ignite;
        }

        @Override
        public void run() {
            IgniteSemaphore sem = ignite.semaphore("sem-worker-1", 1, true, 
true);

            System.out.println("sem created");
            if (sem.tryAcquire()) {
                try {
                    System.out.println("sem aquired");
                } finally {
                    sem.release();
                    System.out.println("sem released");
                }
            } else {
                System.out.println("sem not aquired");
            }
        }
    }


yakov wrote
> Hi Mario!
> 
> Can you please share the code somehow? Reproducible example will be very
> helpful.
> 
> --Yakov
> 
> 2016-02-16 16:57 GMT+03:00 nyname00 &lt;

> mario.stark@

> &gt;:
> 
>> Hi Igniters,
>>
>> I'm getting some strange behavior when I try to call
>> IgniteSemaphore#tryAquire() while holding a lock on a cache element - the
>> method seems block forever.
>>
>> Here's the details:
>>   - create a cache (default, transactional) and get a lock using
>> Lock#tryLock()
>>   - start a Executors.newSingleThreadScheduledExecutor() and schedule a
>> worker to run every n seconds
>>   - in the worker, get a semaphore and call IgniteSemaphore#tryAcquire()
>>   - do some work and call IgniteSemaphore#release()
>> (except for the cache/lock and semaphore no Ignite API calls are made)
>>
>> The whole thing works for a single node, but as soon as I start up an new
>> node (with the same code) the IgniteSemaphore#tryAcquire() call starts
>> blocking.
>>
>> Is this this a known limitation/issue or am I doing something wrong here?
>>
>> Thanks in advance,
>> Mario
>>
>> ps: when I replace the cache-lock with an other semaphore, it works
>>
>>
>>
>> --
>> View this message in context:
>> http://apache-ignite-users.70518.x6.nabble.com/Semaphore-blocking-on-tryAcquire-while-holding-a-cache-lock-tp3031.html
>> Sent from the Apache Ignite Users mailing list archive at Nabble.com.
>>





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