com.hazelcast.map

Interface EntryProcessor<K,V>

Type Parameters:

K - Type of key of a Map.Entry

V - Type of value of a Map.Entry

All Superinterfaces:

Serializable

All Known Implementing Classes:

AbstractEntryProcessor, EntryRemovingProcessor

public interface EntryProcessor<K,V>
extends Serializable

An EntryProcessor passes you a Map.Entry. At the time you receive it the entry is locked and not released until the EntryProcessor completes. This obviates the need to explicitly lock as would be required with a ExecutorService.

Performance can be very high as the data is not moved off the Member partition. This avoids network cost and, if the storage format is InMemoryFormat.OBJECT, then there is no de-serialization or serialization cost.

EntryProcessors execute on the partition thread in a member. Multiple operations on the same partition are queued.

While executing partition migrations are not allowed. Any migrations are queued on the partition thread.

An EntryProcessor may not be re-entrant i.e. it may not access the same Map. Limitation: you can only access data on the same partition.

Note that to modify an entry by using EntryProcessors you should explicitly call the Map.Entry.setValue(V) method of Map.Entry such as:

 
 Override
     public Object process(Map.Entry entry) {
        Value value = entry.getValue();
        // process and modify value
        // ...
        entry.setValue(value);
        return result;
    }
 
 

otherwise EntryProcessor does not guarantee that it will modify the entry.

EntryProcessor instances can be shared between threads. If an EntryProcessor instance contains mutable state, proper concurrency control needs to be provided to coordinate access to mutable state. Another option is to rely on threadlocals. Serialized instances of this interface are used in client-member communication, so changing an implementation's binary format will render it incompatible with its previous versions.

See Also:

AbstractEntryProcessor

Method Summary

Modifier and Type	Method and Description
EntryBackupProcessor<K,V>	getBackupProcessor() Get the entry processor to be applied to backup entries.
Object	process(Map.Entry<K,V> entry) Process the entry without worrying about concurrency.

Method Detail

process

Object process(Map.Entry<K,V> entry)

Process the entry without worrying about concurrency.

Note that to modify an entry by using an EntryProcessor you should explicitly call setValue() method of Map.Entry, for example:

        @Override
        public Object process(Map.Entry entry) {
          Value value = entry.getValue();
          // process and modify value
          // ...
          entry.setValue(value);
          return result;
        }
 

otherwise the EntryProcessor does not guarantee to modify the entry.

The entry's value will be null, if the entry for the key doesn't exist. You can create new mapping by setting a non-null value or remove existing mapping entry by setting the value to null.

Parameters:

entry - entry to be processed

Returns:

a result that will be returned from the method taking the EntryProcessor, such as IMap.executeOnKey()

getBackupProcessor

EntryBackupProcessor<K,V> getBackupProcessor()

Get the entry processor to be applied to backup entries. In case of a readonly execution, null can be returned to indicate that no backups should be made.

Returns:

the back up processor