mirror of
https://github.com/OpenHFT/Chronicle-Map.git
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210 lines
10 KiB
Java
Executable File
210 lines
10 KiB
Java
Executable File
/*
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* Copyright (C) 2012, 2016 higherfrequencytrading.com
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* Copyright (C) 2016 Roman Leventov
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*
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* This program is free software: you can redistribute it and/or modify
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* it under the terms of the GNU Lesser General Public License as published by
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* the Free Software Foundation, either version 3 of the License.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU Lesser General Public License for more details.
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*
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* You should have received a copy of the GNU Lesser General Public License
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* along with this program. If not, see <http://www.gnu.org/licenses/>.
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*/
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package net.openhft.chronicle.map;
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import net.openhft.chronicle.bytes.Byteable;
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import net.openhft.chronicle.core.util.SerializableFunction;
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import net.openhft.chronicle.hash.ChronicleHash;
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import net.openhft.chronicle.hash.serialization.SizedReader;
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import net.openhft.chronicle.hash.serialization.SizedWriter;
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import org.jetbrains.annotations.NotNull;
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import java.io.*;
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import java.util.Map;
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import java.util.concurrent.ConcurrentMap;
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/**
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* {@code ChronicleMap} provides concurrent access to a <i>Chronicle Map key-value store</i> from a
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* JVM process.
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*
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* <p>For information on <ul> <li>how to construct a {@code ChronicleMap}</li> <li>{@code
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* ChronicleMap} flavors and properties</li> <li>available configurations</li> </ul> see {@link
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* ChronicleMapBuilder} documentation.
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*
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* <p>Functionally this interface defines some methods supporting garbage-free off-heap programming:
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* {@link #getUsing(Object, Object)}, {@link #acquireUsing(Object, Object)}.
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*
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* <p>Roughly speaking, {@code ChronicleMap} compares keys and values by their binary serialized
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* form, that shouldn't necessary be the same equality relation as defined by built-in {@link
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* Object#equals(Object)} method, which is prescribed by general {@link Map} contract.
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*
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* <p>Note that {@code ChronicleMap} extends {@link Closeable}, don't forget to {@linkplain #close()
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* close} map when it is no longer needed.
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*
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* @param <K> the map key type
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* @param <V> the map value type
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* @see ChronicleMapBuilder#create()
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* @see ChronicleMapBuilder#createPersistedTo(File)
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* @see ChronicleMapBuilder#createOrRecoverPersistedTo(File, boolean)
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*/
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public interface ChronicleMap<K, V> extends ConcurrentMap<K, V>,
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ChronicleHash<K, MapEntry<K, V>, MapSegmentContext<K, V, ?>,
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ExternalMapQueryContext<K, V, ?>> {
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/**
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* Delegates to {@link ChronicleMapBuilder#of(Class, Class)} for convenience.
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*
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* @param keyClass class of the key type of the Chronicle Map to create
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* @param valueClass class of the value type of the Chronicle Map to create
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* @param <K> the key type of the Chronicle Map to create
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* @param <V> the value type of the Chronicle Map to create
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* @return a new {@code ChronicleMapBuilder} for the given key and value classes
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*/
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static <K, V> ChronicleMapBuilder<K, V> of(Class<K> keyClass, Class<V> valueClass) {
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return ChronicleMapBuilder.of(keyClass, valueClass);
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}
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/**
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* Returns the value to which the specified key is mapped, or {@code null} if this map contains
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* no mapping for the key.
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*
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* <p>If the value class allows reusing, consider {@link #getUsing(Object, Object)} method
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* instead of this to reduce garbage creation. Read <a
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* href="https://github.com/OpenHFT/Chronicle-Map#single-key-queries">the section about usage
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* patterns in the Chronicle Map 3 Tutorial</a> for more.
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*
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* @param key the key whose associated value is to be returned
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* @return the value to which the specified key is mapped after this method call, or {@code
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* null} if no value is mapped
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* @see #getUsing(Object, Object)
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*/
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@Override
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V get(Object key);
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/**
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* Returns the value to which the specified key is mapped, read to the provided {@code value}
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* object, if possible, or returns {@code null}, if this map contains no mapping for the key.
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*
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* <p>If the specified key is present in the map, the value data is read to the provided {@code
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* value} object via value reader's {@link SizedReader#read(net.openhft.chronicle.bytes.Bytes, long, Object)
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* read(StreamingDataInput, size, value)} method. If the value deserializer is able to reuse the
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* given {@code value} object, calling this method instead of {@link #get(Object)} could help to
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* reduce garbage creation.
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*
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* <p>The provided {@code value} object is allowed to be {@code null}, in this case {@code
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* map.getUsing(key, null)} call is semantically equivalent to simple {@code map.get(key)}
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* call.
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*
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* @param key the key whose associated value is to be returned
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* @param usingValue the object to read value data in, if possible
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* @return the value to which the specified key is mapped, or {@code null} if this map contains
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* no mapping for the key
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* @see #get(Object)
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* @see #acquireUsing(Object, Object)
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* @see ChronicleMapBuilder#valueMarshallers(SizedReader, SizedWriter)
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*/
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V getUsing(K key, V usingValue);
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/**
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* Acquire a value for a key, creating if absent.
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*
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* <p>If the specified key is absent in the map, {@linkplain
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* ChronicleMapBuilder#defaultValueProvider(DefaultValueProvider) default value provider} is
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* called. Then this object is put to this map for the specified key.
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*
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* <p>Then, either if the key was initially absent in the map or already present, the value is
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* deserialized just as during {@link #getUsing(Object, Object) getUsing(key, usingValue)} call,
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* passed the same {@code key} and {@code usingValue} as into this method call. This means, as
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* in {@link #getUsing}, {@code usingValue} could safely be {@code null}, in this case a new
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* value instance is created to deserialize the data.
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*
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* <p>In code, {@code acquireUsing} is specified as :
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* <pre>{@code
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* V acquireUsing(K key, V usingValue) {
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* if (!containsKey(key))
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* put(key, defaultValue(key));
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* return getUsing(key, usingValue);
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* }}</pre>
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*
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*
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* <p>Where {@code defaultValue(key)} returns {@link
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* ChronicleMapBuilder#defaultValueProvider(DefaultValueProvider) defaultValueProvider}.
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*
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* <p>If the {@code ChronicleMap} is off-heap updatable, i. e. created via {@link
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* ChronicleMapBuilder} builder (values are {@link Byteable}), there is one more option of what
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* to do if the key is absent in the map. By default, value bytes are just zeroed out, no
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* default value, either provided for key or constant, is put for the absent key.
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*
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* @param key the key whose associated value is to be returned
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* @param usingValue the object to read value data in, if present. Can not be null
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* @return value to which the given key is mapping after this call, either found or created
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* @see #getUsing(Object, Object)
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*/
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V acquireUsing(@NotNull K key, V usingValue);
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@NotNull
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net.openhft.chronicle.core.io.Closeable acquireContext(@NotNull K key, @NotNull V usingValue);
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/**
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* Returns the result of application of the given function to the value to which the given key
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* is mapped. If there is no mapping for the key, {@code null} is returned from {@code
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* getMapped()} call without application of the given function. This method is primarily useful
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* when accessing {@code ChronicleMap} implementation which delegates it's requests to some
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* remote node (server) and pulls the result through serialization/deserialization path, and
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* probably network. In this case, when you actually need only a part of the map value's state
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* (e. g. a single field) it's cheaper to extract it on the server side and transmit lesser
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* bytes.
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*
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* @param key the key whose associated value is to be queried
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* @param function a function to transform the value to the actually needed result,
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* which should be smaller than the map value
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* @param <R> the result type
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* @return the result of applying the function to the mapped value, or {@code null} if there
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* is no mapping for the key
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*/
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<R> R getMapped(K key, @NotNull SerializableFunction<? super V, R> function);
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/**
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* Exports all the entries to a {@link File} storing them in JSON format, an attempt is
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* made where possible to use standard java serialisation and keep the data human readable, data
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* serialized using the custom serialises are converted to a binary format which is not human
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* readable but this is only done if the Keys or Values are not {@link Serializable}.
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* This method can be used in conjunction with {@link ChronicleMap#putAll(File)} and is
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* especially useful if you wish to import/export entries from one chronicle map into another.
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* This import and export of the entries can be performed even when the versions of ChronicleMap
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* differ. This method is not performant and as such we recommend it is not used in performance
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* sensitive code.
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*
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* @param toFile the file to store all the entries to, the entries will be stored in JSON
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* format
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* @throws IOException its not possible store the data to {@code toFile}
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* @see ChronicleMap#putAll(File)
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*/
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void getAll(File toFile) throws IOException;
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/**
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* Imports all the entries from a {@link File}, the {@code fromFile} must be created
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* using or the same format as {@link ChronicleMap#get(Object)}, this method behaves
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* similar to {@link Map#put(Object, Object)} where existing
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* entries are overwritten. A write lock is only held while each individual entry is inserted
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* into the map, not over all the entries in the {@link File}
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*
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* @param fromFile the file containing entries ( in JSON format ) which will be deserialized and
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* {@link Map#put(Object, Object)} into the map
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* @throws IOException its not possible read the {@code fromFile}
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* @see ChronicleMap#getAll(File)
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*/
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void putAll(File fromFile) throws IOException;
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/**
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* @return the class of {@code <V>}
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*/
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Class<V> valueClass();
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}
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