/*
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance
* with the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.flink.api.common.typeutils;
import org.apache.flink.annotation.PublicEvolving;
import org.apache.flink.core.memory.DataInputView;
import org.apache.flink.core.memory.DataOutputView;
import java.io.IOException;
import java.io.Serializable;
/**
* This interface describes the methods that are required for a data type to be handled by the Flink
* runtime. Specifically, this interface contains the serialization and copying methods.
* <p>
* The methods in this class are assumed to be stateless, such that it is effectively thread safe. Stateful
* implementations of the methods may lead to unpredictable side effects and will compromise both stability and
* correctness of the program.
*
* @param <T> The data type that the serializer serializes.
*/
@PublicEvolving
public abstract class TypeSerializer<T> implements TypeDeserializer<T>, Serializable {
private static final long serialVersionUID = 1L;
// --------------------------------------------------------------------------------------------
// General information about the type and the serializer
// --------------------------------------------------------------------------------------------
/**
* Gets whether the type is an immutable type.
*
* @return True, if the type is immutable.
*/
public abstract boolean isImmutableType();
/**
* Creates a deep copy of this serializer if it is necessary, i.e. if it is stateful. This
* can return itself if the serializer is not stateful.
*
* We need this because Serializers might be used in several threads. Stateless serializers
* are inherently thread-safe while stateful serializers might not be thread-safe.
*/
public abstract TypeSerializer<T> duplicate();
// --------------------------------------------------------------------------------------------
// Instantiation & Cloning
// --------------------------------------------------------------------------------------------
/**
* Creates a new instance of the data type.
*
* @return A new instance of the data type.
*/
public abstract T createInstance();
/**
* Creates a deep copy of the given element in a new element.
*
* @param from The element reuse be copied.
* @return A deep copy of the element.
*/
public abstract T copy(T from);
/**
* Creates a copy from the given element.
* The method makes an attempt to store the copy in the given reuse element, if the type is mutable.
* This is, however, not guaranteed.
*
* @param from The element to be copied.
* @param reuse The element to be reused. May or may not be used.
* @return A deep copy of the element.
*/
public abstract T copy(T from, T reuse);
// --------------------------------------------------------------------------------------------
/**
* Gets the length of the data type, if it is a fix length data type.
*
* @return The length of the data type, or <code>-1</code> for variable length data types.
*/
public abstract int getLength();
// --------------------------------------------------------------------------------------------
/**
* Serializes the given record to the given target output view.
*
* @param record The record to serialize.
* @param target The output view to write the serialized data to.
*
* @throws IOException Thrown, if the serialization encountered an I/O related error. Typically raised by the
* output view, which may have an underlying I/O channel to which it delegates.
*/
public abstract void serialize(T record, DataOutputView target) throws IOException;
/**
* De-serializes a record from the given source input view.
*
* @param source The input view from which to read the data.
* @return The deserialized element.
*
* @throws IOException Thrown, if the de-serialization encountered an I/O related error. Typically raised by the
* input view, which may have an underlying I/O channel from which it reads.
*/
public abstract T deserialize(DataInputView source) throws IOException;
/**
* De-serializes a record from the given source input view into the given reuse record instance if mutable.
*
* @param reuse The record instance into which to de-serialize the data.
* @param source The input view from which to read the data.
* @return The deserialized element.
*
* @throws IOException Thrown, if the de-serialization encountered an I/O related error. Typically raised by the
* input view, which may have an underlying I/O channel from which it reads.
*/
public abstract T deserialize(T reuse, DataInputView source) throws IOException;
/**
* Copies exactly one record from the source input view to the target output view. Whether this operation
* works on binary data or partially de-serializes the record to determine its length (such as for records
* of variable length) is up to the implementer. Binary copies are typically faster. A copy of a record containing
* two integer numbers (8 bytes total) is most efficiently implemented as
* {@code target.write(source, 8);}.
*
* @param source The input view from which to read the record.
* @param target The target output view to which to write the record.
*
* @throws IOException Thrown if any of the two views raises an exception.
*/
public abstract void copy(DataInputView source, DataOutputView target) throws IOException;
public abstract boolean equals(Object obj);
/**
* Returns true if the given object can be equaled with this object. If not, it returns false.
*
* @param obj Object which wants to take part in the equality relation
* @return true if obj can be equaled with this, otherwise false
*/
public abstract boolean canEqual(Object obj);
public abstract int hashCode();
// --------------------------------------------------------------------------------------------
// Serializer configuration snapshotting & compatibility
// --------------------------------------------------------------------------------------------
/**
* Create a snapshot of the serializer's current configuration to be stored along with the managed state it is
* registered to (if any - this method is only relevant if this serializer is registered for serialization of
* managed state).
*
* <p>The configuration snapshot should contain information about the serializer's parameter settings and its
* serialization format. When a new serializer is registered to serialize the same managed state that this
* serializer was registered to, the returned configuration snapshot can be used to ensure compatibility
* of the new serializer and determine if state migration is required.
*
* @see TypeSerializerConfigSnapshot
*
* @return snapshot of the serializer's current configuration (cannot be {@code null}).
*/
public abstract TypeSerializerConfigSnapshot snapshotConfiguration();
/**
* Ensure compatibility of this serializer with a preceding serializer that was registered for serialization of
* the same managed state (if any - this method is only relevant if this serializer is registered for
* serialization of managed state).
*
* The compatibility check in this method should be performed by inspecting the preceding serializer's configuration
* snapshot. The method may reconfigure the serializer (if required and possible) so that it may be compatible,
* or provide a signaling result that informs Flink that state migration is necessary before continuing to use
* this serializer.
*
* <p>The result can be one of the following:
* <ul>
* <li>{@link CompatibilityResult#compatible()}: this signals Flink that this serializer is compatible, or
* has been reconfigured to be compatible, to continue reading previous data, and that the
* serialization schema remains the same. No migration needs to be performed.</li>
*
* <li>{@link CompatibilityResult#requiresMigration(TypeDeserializer)}: this signals Flink that
* migration needs to be performed, because this serializer is not compatible, or cannot be reconfigured to be
* compatible, for previous data. Furthermore, in the case that the preceding serializer cannot be found or
* restored to read the previous data to perform the migration, the provided convert deserializer can be
* used as a fallback resort.</li>
*
* <li>{@link CompatibilityResult#requiresMigration()}: this signals Flink that migration needs to be
* performed, because this serializer is not compatible, or cannot be reconfigured to be compatible, for
* previous data. If the preceding serializer cannot be found (either its implementation changed or it was
* removed from the classpath) then the migration will fail due to incapability to read previous data.</li>
* </ul>
*
* @see CompatibilityResult
*
* @param configSnapshot configuration snapshot of a preceding serializer for the same managed state
*
* @return the determined compatibility result (cannot be {@code null}).
*/
public abstract CompatibilityResult<T> ensureCompatibility(TypeSerializerConfigSnapshot configSnapshot);
}