Package org.apache.ignite.lang

## Annotation Type IgniteAsyncCallback

-     @Retention(RUNTIME)
      @Target(TYPE)
      public @interface IgniteAsyncCallback

  If callback has this annotation then it will be executing in another thread.

  Currently this annotation is supported for:

  1. `ContinuousQuery` - `CacheEntryUpdatedListener` and `CacheEntryEventFilter`.

  For example, if `filter` or `CacheEntryListener` has the annotation then callbacks will be executing to asyncCallback thread pool. It allows to use cache API in a callbacks. This thread pool can be configured by `IgniteConfiguration.setAsyncCallbackPoolSize(int)`.

  # Example

  As an example, suppose we have cache with `'Person'` objects and we need to query all persons with salary above then 1000. Also remote filter will update some entries.

  Here is the `Person` class:

       public class Person {
           // Name.
           private String name;

           // Salary.
           private double salary;

           ...
       }

  Here is the `ExampleCacheEntryFilter` class:

       @IgniteAsyncCallback
       public class ExampleCacheEntryFilter implements CacheEntryEventFilter<Integer, Person> {
           @IgniteInstanceResource
           private Ignite ignite;

           // Continuous listener will be notified for persons with salary above 1000.
           // Filter increases salary for some person on 100. Without @IgniteAsyncCallback annotation
           // this operation is not safe.
           public boolean evaluate(CacheEntryEvent<? extends K, ? extends V> evt) throws CacheEntryListenerException {
               Person p = evt.getValue();

               if (p.getSalary() > 1000)
                   return true;

               ignite.cache("Person").put(evt.getKey(), new Person(p.getName(), p.getSalary() + 100));

               return false;
           }
       }

  Query with asynchronous callback execute as usually:

       // Create new continuous query.
       ContinuousQuery<Long, Person> qry = new ContinuousQuery<>();

       // Callback that is called locally when update notifications are received.
       // It simply prints out information about all created persons.
       qry.setLocalListener((evts) -> {
           for (CacheEntryEvent<? extends Long, ? extends Person> e : evts) {
               Person p = e.getValue();

               System.out.println(p.getFirstName() + " " + p.getLastName() + "'s salary is " + p.getSalary());
           }
       });

       // Sets remote filter.
       qry.setRemoteFilterFactory(() -> new ExampleCacheEntryFilter());

       // Execute query.
       QueryCursor<Cache.Entry<Long, Person>> cur = cache.query(qry);

  See Also:
    `IgniteConfiguration.getAsyncCallbackPoolSize()`, `AbstractContinuousQuery.getRemoteFilterFactory()`, `ContinuousQuery.getLocalListener()`