com.hazelcast.jet.core

## Class AbstractProcessor

- java.lang.Object
- - com.hazelcast.jet.core.AbstractProcessor

- All Implemented Interfaces:
    Processor

      public abstract class AbstractProcessor
      extends Object
      implements Processor

  Base class to implement custom processors. Simplifies the contract of `Processor` with several levels of convenience:
  1. `Processor.init(Outbox, Context)` retains the supplied outbox and the logger retrieved from the context.
  2. `process(n, inbox)` delegates to the matching `tryProcessN()` with each item received in the inbox.
  3. There is also the general `tryProcess(int, Object)` to which the `tryProcessN` methods delegate by default. It is convenient to override it when the processor doesn't care which edge an item originates from. Another convenient idiom is to override `tryProcessN()` for one or two specially treated edges and override `tryProcess(int, Object)` to process the rest of the edges, which are treated uniformly.
  4. The `tryEmit(...)` methods avoid the need to deal with `Outbox` directly.
  5. The `emitFromTraverser(...)` methods handle the boilerplate of emission from a traverser. They are especially useful in the `Processor.complete()` step when there is a collection of items to emit. The `Traversers` class contains traversers tailored to simplify the implementation of `complete()`.
  6. The `FlatMapper` class additionally simplifies the usage of `emitFromTraverser()` inside `tryProcess()`, in a scenario where an input item results in a collection of output items. `FlatMapper` is obtained from one of the factory methods `flatMapper(...)`.

- - ### Nested Class Summary

    Nested Classes
    Modifier and Type | Class and Description
    --- | ---
    `protected class` | `AbstractProcessor.FlatMapper<T,R>` A helper that simplifies the implementation of `tryProcess(ordinal, item)` for emitting collections.

    - ### Nested classes/interfaces inherited from interface com.hazelcast.jet.core.Processor

      `Processor.Context`

  - ### Constructor Summary

    Constructors
    Constructor and Description
    `AbstractProcessor()`

  - ### Method Summary

    All Methods Instance Methods Concrete Methods
    Modifier and Type | Method and Description
    --- | ---
    `protected <E> boolean` | `emitFromTraverser(int[] ordinals, Traverser<E> traverser)` Obtains items from the traverser and offers them to the outbox's buckets identified in the supplied array.
    `protected <E> boolean` | `emitFromTraverser(int ordinal, Traverser<E> traverser)` Obtains items from the traverser and offers them to the outbox's buckets identified in the supplied array.
    `protected boolean` | `emitFromTraverser(Traverser<?> traverser)` Convenience for `emitFromTraverser(int, Traverser)` which emits to all ordinals.
    `protected <T extends Map.Entry<?,?>> boolean` | `emitFromTraverserToSnapshot(Traverser<T> traverser)` Obtains items from the traverser and offers them to the snapshot bucket of the outbox.
    `protected <T,R> AbstractProcessor.FlatMapper<T,R>` | `flatMapper(Function<? super T,? extends Traverser<? extends R>> mapper)` Factory of `AbstractProcessor.FlatMapper`.
    `protected <T,R> AbstractProcessor.FlatMapper<T,R>` | `flatMapper(int[] ordinals, Function<? super T,? extends Traverser<? extends R>> mapper)` Factory of `AbstractProcessor.FlatMapper`.
    `protected <T,R> AbstractProcessor.FlatMapper<T,R>` | `flatMapper(int ordinal, Function<? super T,? extends Traverser<? extends R>> mapper)` Factory of `AbstractProcessor.FlatMapper`.
    `protected ILogger` | `getLogger()` Returns the logger associated with this processor instance.
    `protected Outbox` | `getOutbox()`
    `void` | `init(Outbox outbox, Processor.Context context)` Initializes this processor with the outbox that the processing methods must use to deposit their output items.
    `protected void` | `init(Processor.Context context)` Method that can be overridden to perform any necessary initialization for the processor.
    `void` | `process(int ordinal, Inbox inbox)` Implements the boilerplate of dispatching against the ordinal, taking items from the inbox one by one, and invoking the processing logic on each.
    `void` | `restoreFromSnapshot(Inbox inbox)` Implements the boilerplate of polling the inbox, casting the items to `Map.Entry`, and extracting the key and value.
    `protected void` | `restoreFromSnapshot(Object key, Object value)` Called to restore one key-value pair from the snapshot to processor's internal state.
    `protected boolean` | `tryEmit(int[] ordinals, Object item)` Offers the item to the outbox buckets identified in the supplied array.
    `protected boolean` | `tryEmit(int ordinal, Object item)` Offers the item to the outbox bucket at the supplied ordinal.
    `protected boolean` | `tryEmit(Object item)` Offers the item to all the outbox buckets (except the snapshot outbox).
    `protected boolean` | `tryEmitToSnapshot(Object key, Object value)` Offers one key-value pair to the snapshot bucket.
    `protected boolean` | `tryProcess(int ordinal, Object item)` Tries to process the supplied input item, which was received from the edge with the supplied ordinal.
    `protected boolean` | `tryProcess0(Object item)` Tries to process the supplied input item, which was received from the edge with ordinal 0.
    `protected boolean` | `tryProcess1(Object item)` Tries to process the supplied input item, which was received from the edge with ordinal 1.
    `protected boolean` | `tryProcess2(Object item)` Tries to process the supplied input item, which was received from the edge with ordinal 2.
    `protected boolean` | `tryProcess3(Object item)` Tries to process the supplied input item, which was received from the edge with ordinal 3.
    `protected boolean` | `tryProcess4(Object item)` Tries to process the supplied input item, which was received from the edge with ordinal 4.

    - ### Methods inherited from class java.lang.Object

      `clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

    - ### Methods inherited from interface com.hazelcast.jet.core.Processor

      `close, complete, completeEdge, finishSnapshotRestore, isCooperative, saveToSnapshot, tryProcess, tryProcessWatermark`

- - ### Constructor Detail

    - #### AbstractProcessor

          public AbstractProcessor()

  - ### Method Detail

    - #### init

          public final void init(@Nonnull
                                 Outbox outbox,
                                 @Nonnull
                                 Processor.Context context)

      Description copied from interface: `Processor`
      Initializes this processor with the outbox that the processing methods must use to deposit their output items. This method will be called exactly once and strictly before any calls to processing methods (`Processor.process(int, Inbox)` and `Processor.complete()`).

      The default implementation does nothing.

      Specified by:
        `init` in interface `Processor`

    - #### restoreFromSnapshot

          public final void restoreFromSnapshot(@Nonnull
                                                Inbox inbox)

      Implements the boilerplate of polling the inbox, casting the items to `Map.Entry`, and extracting the key and value. Forwards each key-value pair to `restoreFromSnapshot(Object, Object)`.
      Specified by:
        `restoreFromSnapshot` in interface `Processor`

    - #### process

          public final void process(int ordinal,
                                    @Nonnull
                                    Inbox inbox)

      Implements the boilerplate of dispatching against the ordinal, taking items from the inbox one by one, and invoking the processing logic on each.
      Specified by:
        `process` in interface `Processor`
      Parameters:
        `ordinal` - ordinal of the inbound edge
        `inbox` - the inbox containing the pending items

    - #### init

          protected void init(@Nonnull
                              Processor.Context context)
                       throws Exception

      Method that can be overridden to perform any necessary initialization for the processor. It is called exactly once and strictly before any of the processing methods (`process()` and `Processor.complete()`), but after the outbox and `logger` have been initialized.

      Subclasses are not required to call this superclass method, it does nothing.

      Parameters:
        `context` - the `context` associated with this processor
      Throws:
        `Exception`

    - #### tryProcess

          protected boolean tryProcess(int ordinal,
                                       @Nonnull
                                       Object item)
                                throws Exception

      Tries to process the supplied input item, which was received from the edge with the supplied ordinal. May choose to process only partially and return `false`, in which case it will be called again later with the same `(ordinal, item)` combination before any other processing method is called.

      The default implementation throws an `UnsupportedOperationException`.

      NOTE: unless the processor doesn't differentiate between its inbound edges, the first choice should be leaving this method alone and instead overriding the specific `tryProcessN()` methods for each ordinal the processor expects.

      Parameters:
        `ordinal` - ordinal of the edge that delivered the item
        `item` - item to be processed
      Returns:
        `true` if this item has now been processed, `false` otherwise.
      Throws:
        `Exception`

    - #### tryProcess0

          protected boolean tryProcess0(@Nonnull
                                        Object item)
                                 throws Exception

      Tries to process the supplied input item, which was received from the edge with ordinal 0. May choose to process only partially and return `false`, in which case it will be called again later with the same item before any other processing method is called.

      The default implementation delegates to `tryProcess(0, item)`.

      Parameters:
        `item` - item to be processed
      Returns:
        `true` if this item has now been processed, `false` otherwise.
      Throws:
        `Exception`

    - #### tryProcess1

          protected boolean tryProcess1(@Nonnull
                                        Object item)
                                 throws Exception

      Tries to process the supplied input item, which was received from the edge with ordinal 1. May choose to process only partially and return `false`, in which case it will be called again later with the same item before any other processing method is called.

      The default implementation delegates to `tryProcess(1, item)`.

      Parameters:
        `item` - item to be processed
      Returns:
        `true` if this item has now been processed, `false` otherwise.
      Throws:
        `Exception`

    - #### tryProcess2

          protected boolean tryProcess2(@Nonnull
                                        Object item)
                                 throws Exception

      Tries to process the supplied input item, which was received from the edge with ordinal 2. May choose to process only partially and return `false`, in which case it will be called again later with the same item before any other processing method is called.

      The default implementation delegates to `tryProcess(2, item)`.

      Parameters:
        `item` - item to be processed
      Returns:
        `true` if this item has now been processed, `false` otherwise.
      Throws:
        `Exception`

    - #### tryProcess3

          protected boolean tryProcess3(@Nonnull
                                        Object item)
                                 throws Exception

      Tries to process the supplied input item, which was received from the edge with ordinal 3. May choose to process only partially and return `false`, in which case it will be called again later with the same item before any other processing method is called.

      The default implementation delegates to `tryProcess(3, item)`.

      Parameters:
        `item` - item to be processed
      Returns:
        `true` if this item has now been processed, `false` otherwise.
      Throws:
        `Exception`

    - #### tryProcess4

          protected boolean tryProcess4(@Nonnull
                                        Object item)
                                 throws Exception

      Tries to process the supplied input item, which was received from the edge with ordinal 4. May choose to process only partially and return `false`, in which case it will be called again later with the same item before any other processing method is called.

      The default implementation delegates to `tryProcess(4, item)`.

      Parameters:
        `item` - item to be processed
      Returns:
        `true` if this item has now been processed, `false` otherwise.
      Throws:
        `Exception`

    - #### restoreFromSnapshot

          protected void restoreFromSnapshot(@Nonnull
                                             Object key,
                                             @Nonnull
                                             Object value)

      Called to restore one key-value pair from the snapshot to processor's internal state.

      The default implementation throws an `UnsupportedOperationException`, but it will not be called unless you override `Processor.saveToSnapshot()`.

      Parameters:
        `key` - key of the entry from the snapshot
        `value` - value of the entry from the snapshot

    - #### getLogger

          protected final ILogger getLogger()

      Returns the logger associated with this processor instance.

    - #### getOutbox

          protected final Outbox getOutbox()

    - #### tryEmit

          @CheckReturnValue
          protected final boolean tryEmit(int ordinal,
                                                            @Nonnull
                                                            Object item)

      Offers the item to the outbox bucket at the supplied ordinal.

      Emitted items should not be subsequently mutated because the same instance might be used by a downstream processor in a different thread, causing concurrent access.

      Returns:
        `true`, if the item was accepted. If `false` is returned, the call must be retried later with the same (or equal) item.

    - #### tryEmit

          @CheckReturnValue
          protected final boolean tryEmit(@Nonnull
                                                            Object item)

      Offers the item to all the outbox buckets (except the snapshot outbox).

      Emitted items should not be subsequently mutated because the same instance might be used by a downstream processor in a different thread, causing concurrent access.

      Returns:
        `true`, if the item was accepted. If `false` is returned, the call must be retried later with the same (or equal) item.

    - #### tryEmit

          @CheckReturnValue
          protected final boolean tryEmit(@Nonnull
                                                            int[] ordinals,
                                                            @Nonnull
                                                            Object item)

      Offers the item to the outbox buckets identified in the supplied array.

      Emitted items should not be subsequently mutated because the same instance might be used by a downstream processor in a different thread, causing concurrent access.

      Returns:
        `true`, if the item was accepted. If `false` is returned, the call must be retried later with the same (or equal) item.

    - #### emitFromTraverser

          protected final <E> boolean emitFromTraverser(@Nonnull
                                                        int[] ordinals,
                                                        @Nonnull
                                                        Traverser<E> traverser)

      Obtains items from the traverser and offers them to the outbox's buckets identified in the supplied array. If the outbox refuses an item, it backs off and returns `false`.

      Emitted items should not be subsequently mutated because the same instance might be used by a downstream processor in a different thread, causing concurrent access.

      If this method returns `false`, then the caller must retain the traverser and pass it again in the subsequent invocation of this method, so as to resume emitting where it left off.

      For simplified usage from `tryProcess(ordinal, item)` methods, see `AbstractProcessor.FlatMapper`.

      Parameters:
        `ordinals` - ordinals of the target bucket
        `traverser` - traverser over items to emit
      Returns:
        whether the traverser has been exhausted

    - #### emitFromTraverser

          protected final <E> boolean emitFromTraverser(int ordinal,
                                                        @Nonnull
                                                        Traverser<E> traverser)

      Obtains items from the traverser and offers them to the outbox's buckets identified in the supplied array. If the outbox refuses an item, it backs off and returns `false`.

      Emitted items should not be subsequently mutated because the same instance might be used by a downstream processor in a different thread, causing concurrent access.

      If this method returns `false`, then the caller must retain the traverser and pass it again in the subsequent invocation of this method, so as to resume emitting where it left off.

      For simplified usage in `tryProcess(ordinal, item)` methods, see `AbstractProcessor.FlatMapper`.

      Parameters:
        `ordinal` - ordinal of the target bucket
        `traverser` - traverser over items to emit
      Returns:
        whether the traverser has been exhausted

    - #### emitFromTraverser

          protected final boolean emitFromTraverser(@Nonnull
                                                    Traverser<?> traverser)

      Convenience for `emitFromTraverser(int, Traverser)` which emits to all ordinals.

    - #### tryEmitToSnapshot

          @CheckReturnValue
          protected final boolean tryEmitToSnapshot(@Nonnull
                                                                      Object key,
                                                                      @Nonnull
                                                                      Object value)

      Offers one key-value pair to the snapshot bucket.

      The type of the offered key determines which processors receive the key and value pair when it is restored. If the key is of type `BroadcastKey`, the entry will be restored to all processor instances. Otherwise, the key will be distributed according to default partitioning and only a single processor instance will receive the key.

      Keys and values offered to snapshot are serialized and can be further mutated as soon as this method returns.

      Returns:
        `true`, if the item was accepted. If `false` is returned, the call must be retried later with the same (or equal) key and value.

    - #### emitFromTraverserToSnapshot

          protected final <T extends Map.Entry<?,?>> boolean emitFromTraverserToSnapshot(@Nonnull
                                                                                         Traverser<T> traverser)

      Obtains items from the traverser and offers them to the snapshot bucket of the outbox. Each item is a `Map.Entry` and its key and value are passed as the two arguments of `tryEmitToSnapshot(Object, Object)`. If the outbox refuses an item, it backs off and returns `false`.

      Keys and values offered to snapshot are serialized and can be further mutated as soon as this method returns.

      If this method returns `false`, then the caller must retain the traverser and pass it again in the subsequent invocation of this method, so as to resume emitting where it left off.

      The type of the offered key determines which processors receive the key and value pair when it is restored. If the key is of type `BroadcastKey`, the entry will be restored to all processor instances. Otherwise, the key will be distributed according to default partitioning and only a single processor instance will receive the key.

      Parameters:
        `traverser` - traverser over the items to emit to the snapshot
      Returns:
        whether the traverser has been exhausted

    - #### flatMapper

          @Nonnull
          protected final <T,R> AbstractProcessor.FlatMapper<T,R> flatMapper(int ordinal,
                                                                                      @Nonnull
                                                                                      Function<? super T,? extends Traverser<? extends R>> mapper)

      Factory of `AbstractProcessor.FlatMapper`. The `FlatMapper` will emit items to the given output ordinal.

    - #### flatMapper

          @Nonnull
          protected final <T,R> AbstractProcessor.FlatMapper<T,R> flatMapper(@Nonnull
                                                                                      Function<? super T,? extends Traverser<? extends R>> mapper)

      Factory of `AbstractProcessor.FlatMapper`. The `FlatMapper` will emit items to all defined output ordinals.

    - #### flatMapper

          @Nonnull
          protected final <T,R> AbstractProcessor.FlatMapper<T,R> flatMapper(@Nonnull
                                                                                      int[] ordinals,
                                                                                      @Nonnull
                                                                                      Function<? super T,? extends Traverser<? extends R>> mapper)

      Factory of `AbstractProcessor.FlatMapper`. The `FlatMapper` will emit items to the ordinals identified in the array.

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