mirror of
https://github.com/OpenHFT/Chronicle-Map.git
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63 lines
3.0 KiB
Java
63 lines
3.0 KiB
Java
/*
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* Copyright 2014 Higher Frequency Trading http://www.higherfrequencytrading.com
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package net.openhft.chronicle.map;
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import net.openhft.lang.io.Bytes;
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import net.openhft.lang.model.Byteable;
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import java.io.Serializable;
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/**
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* Strategy of preparing bytes of off-heap memory before assigning them into {@link Byteable}
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* value during {@link ChronicleMap#acquireUsing(Object, Object)
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* chronicleMap.acquireUsing()} call, when the given key is absent in the map. Example: if you
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* want {@code 1L} to be the off-heap updatable ChronicleMap's {@linkplain
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* ChronicleMapBuilder#defaultValue(Object) default value}, the most simple way
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* to achieve this is to {@linkplain ChronicleMapBuilder#prepareValueBytesOnAcquire(
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* PrepareValueBytes) configure} custom {@code PrepareValueBytes} strategy in {@link
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* ChronicleMapBuilder}: <pre>{@code
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* ChronicleMapBuilder.of(Key.class, LongValue.class)
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* .prepareValueBytesOnAcquire((bytes, k) -> bytes.writeLong(1L))
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* ...
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* .create();}</pre>
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*
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* <p>Although the value type is not used in the API, {@link PrepareValueBytes} is not intended
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* to be generic by value type, because strategy should know the value layout and
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* {@linkplain Byteable#maxSize() how much bytes} does it take in memory.
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*
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* @param <K> the key type of {@link ChronicleMap}, on which {@code acquireUsing()} is queried
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* @param <V> the value type of {@link ChronicleMap}, on which {@code acquireUsing()} is queried
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* @see ChronicleMapBuilder#prepareValueBytesOnAcquire(PrepareValueBytes)
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*/
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public interface PrepareValueBytes<K, V> extends Serializable {
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/**
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* Prepares bytes before assigning them into {@link Byteable}. The given bytes' position
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* corresponds to the start of value bytes to be assigned into. This method should increment
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* the given bytes' position by {@linkplain Byteable#maxSize() the value size}. Bytes' contents
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* outside of this range shouldn't be altered.
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*
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* @param bytes the bytes, positioned at the first value byte. Bytes' {@linkplain Bytes#limit(
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* long) limit} and {@linkplain Bytes#remaining()} are not specified, but it is guaranteed that
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* the latter is not less than {@linkplain Byteable#maxSize() the value size}.
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* @param key the key which is absent in the {@link ChronicleMap} during {@link
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* ChronicleMap#acquireUsing(Object, Object) acquireUsing()} call and value bytes are prepared
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* for
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*/
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void prepare(Bytes bytes, K key);
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}
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