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/*
 * Copyright (C) 2011 The Guava Authors
 *
 * Licensed 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.weakref.jmx.internal.guava.cache;

import org.weakref.jmx.internal.guava.annotations.Beta;
import org.weakref.jmx.internal.guava.annotations.GwtCompatible;
import org.weakref.jmx.internal.guava.base.Function;
import org.weakref.jmx.internal.guava.collect.ImmutableMap;
import org.weakref.jmx.internal.guava.util.concurrent.ExecutionError;
import org.weakref.jmx.internal.guava.util.concurrent.UncheckedExecutionException;

import java.util.concurrent.ConcurrentMap;
import java.util.concurrent.ExecutionException;

/**
 * A semi-persistent mapping from keys to values. Values are automatically loaded by the cache,
 * and are stored in the cache until either evicted or manually invalidated.
 *
 * 

Implementations of this interface are expected to be thread-safe, and can be safely accessed * by multiple concurrent threads. * *

When evaluated as a {@link Function}, a cache yields the same result as invoking * {@link #getUnchecked}. * *

Note that while this class is still annotated as {@link Beta}, the API is frozen from a * consumer's standpoint. In other words existing methods are all considered {@code non-Beta} and * won't be changed without going through an 18 month deprecation cycle; however new methods may be * added at any time. * * @author Charles Fry * @since 11.0 */ @Beta @GwtCompatible public interface LoadingCache extends Cache, Function { /** * Returns the value associated with {@code key} in this cache, first loading that value if * necessary. No observable state associated with this cache is modified until loading completes. * *

If another call to {@link #get} or {@link #getUnchecked} is currently loading the value for * {@code key}, simply waits for that thread to finish and returns its loaded value. Note that * multiple threads can concurrently load values for distinct keys. * *

Caches loaded by a {@link CacheLoader} will call {@link CacheLoader#load} to load new values * into the cache. Newly loaded values are added to the cache using * {@code Cache.asMap().putIfAbsent} after loading has completed; if another value was associated * with {@code key} while the new value was loading then a removal notification will be sent for * the new value. * *

If the cache loader associated with this cache is known not to throw checked * exceptions, then prefer {@link #getUnchecked} over this method. * * @throws ExecutionException if a checked exception was thrown while loading the value. ({@code * ExecutionException} is thrown even if * computation was interrupted by an {@code InterruptedException}.) * @throws UncheckedExecutionException if an unchecked exception was thrown while loading the * value * @throws ExecutionError if an error was thrown while loading the value */ V get(K key) throws ExecutionException; /** * Returns the value associated with {@code key} in this cache, first loading that value if * necessary. No observable state associated with this cache is modified until loading * completes. Unlike {@link #get}, this method does not throw a checked exception, and thus should * only be used in situations where checked exceptions are not thrown by the cache loader. * *

If another call to {@link #get} or {@link #getUnchecked} is currently loading the value for * {@code key}, simply waits for that thread to finish and returns its loaded value. Note that * multiple threads can concurrently load values for distinct keys. * *

Caches loaded by a {@link CacheLoader} will call {@link CacheLoader#load} to load new values * into the cache. Newly loaded values are added to the cache using * {@code Cache.asMap().putIfAbsent} after loading has completed; if another value was associated * with {@code key} while the new value was loading then a removal notification will be sent for * the new value. * *

Warning: this method silently converts checked exceptions to unchecked exceptions, * and should not be used with cache loaders which throw checked exceptions. In such cases use * {@link #get} instead. * * @throws UncheckedExecutionException if an exception was thrown while loading the value. (As * explained in the last paragraph above, this should be an unchecked exception only.) * @throws ExecutionError if an error was thrown while loading the value */ V getUnchecked(K key); /** * Returns a map of the values associated with {@code keys}, creating or retrieving those values * if necessary. The returned map contains entries that were already cached, combined with newly * loaded entries; it will never contain null keys or values. * *

Caches loaded by a {@link CacheLoader} will issue a single request to * {@link CacheLoader#loadAll} for all keys which are not already present in the cache. All * entries returned by {@link CacheLoader#loadAll} will be stored in the cache, over-writing * any previously cached values. This method will throw an exception if * {@link CacheLoader#loadAll} returns {@code null}, returns a map containing null keys or values, * or fails to return an entry for each requested key. * *

Note that duplicate elements in {@code keys}, as determined by {@link Object#equals}, will * be ignored. * * @throws ExecutionException if a checked exception was thrown while loading the value. ({@code * ExecutionException} is thrown even if * computation was interrupted by an {@code InterruptedException}.) * @throws UncheckedExecutionException if an unchecked exception was thrown while loading the * values * @throws ExecutionError if an error was thrown while loading the values * @since 11.0 */ ImmutableMap getAll(Iterable keys) throws ExecutionException; /** * @deprecated Provided to satisfy the {@code Function} interface; use {@link #get} or * {@link #getUnchecked} instead. * @throws UncheckedExecutionException if an exception was thrown while loading the value. (As * described in the documentation for {@link #getUnchecked}, {@code LoadingCache} should be * used as a {@code Function} only with cache loaders that throw only unchecked exceptions.) */ @Deprecated @Override V apply(K key); /** * Loads a new value for key {@code key}, possibly asynchronously. While the new value is loading * the previous value (if any) will continue to be returned by {@code get(key)} unless it is * evicted. If the new value is loaded successfully it will replace the previous value in the * cache; if an exception is thrown while refreshing the previous value will remain, and the * exception will be logged (using {@link java.util.logging.Logger}) and swallowed. * *

Caches loaded by a {@link CacheLoader} will call {@link CacheLoader#reload} if the * cache currently contains a value for {@code key}, and {@link CacheLoader#load} otherwise. * Loading is asynchronous only if {@link CacheLoader#reload} was overridden with an * asynchronous implementation. * *

Returns without doing anything if another thread is currently loading the value for * {@code key}. If the cache loader associated with this cache performs refresh asynchronously * then this method may return before refresh completes. * * @since 11.0 */ void refresh(K key); /** * {@inheritDoc} * *

Note that although the view is modifiable, no method on the returned map will ever * cause entries to be automatically loaded. */ @Override ConcurrentMap asMap(); }





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