package com.comphenix.protocol.utility;
import java.lang.reflect.Method;
import java.util.concurrent.ConcurrentMap;
import java.util.concurrent.TimeUnit;
import com.comphenix.protocol.reflect.FieldAccessException;
import com.google.common.base.Ticker;
import com.google.common.cache.CacheBuilder;
import com.google.common.cache.CacheLoader;
import com.google.common.cache.RemovalListener;
/**
* Represents a Guava CacheBuilder that is compatible with both Guava 10 and 13.
*
* @author Kristian
*/
public class SafeCacheBuilder<K, V> {
private CacheBuilder<K, V> builder;
private static Method BUILD_METHOD;
private static Method AS_MAP_METHOD;
@SuppressWarnings("unchecked")
private SafeCacheBuilder() {
builder = (CacheBuilder<K, V>) CacheBuilder.newBuilder();
}
/**
* Construct a new safe cache builder.
*
* @return A new cache builder.
*/
public static <K, V> SafeCacheBuilder<K, V> newBuilder() {
return new SafeCacheBuilder<K, V>();
}
/**
* Guides the allowed concurrency among update operations. Used as a hint
* for internal sizing. The table is internally partitioned to try to permit
* the indicated number of concurrent updates without contention. Because
* assignment of entries to these partitions is not necessarily uniform, the
* actual concurrency observed may vary. Ideally, you should choose a value
* to accommodate as many threads as will ever concurrently modify the
* table. Using a significantly higher value than you need can waste space
* and time, and a significantly lower value can lead to thread contention.
* But overestimates and underestimates within an order of magnitude do not
* usually have much noticeable impact. A value of one permits only one
* thread to modify the cache at a time, but since read operations can
* proceed concurrently, this still yields higher concurrency than full
* synchronization. Defaults to 4.
*
* <p>
* <b>Note:</b>The default may change in the future. If you care about this
* value, you should always choose it explicitly.
*
* @throws IllegalArgumentException if {@code concurrencyLevel} is
* nonpositive
* @throws IllegalStateException if a concurrency level was already set
*/
public SafeCacheBuilder<K, V> concurrencyLevel(int concurrencyLevel) {
builder.concurrencyLevel(concurrencyLevel);
return this;
}
/**
* Specifies that each entry should be automatically removed from the cache
* once a fixed duration has elapsed after the entry's creation, or last
* access. Access time is reset by {@link com.google.common.cache.Cache#get Cache.get()} and
* {@link com.google.common.cache.Cache#getUnchecked Cache.getUnchecked()},
* but not by operations on the view returned by
* {@link com.google.common.cache.Cache#asMap() Cache.asMap()}.
*
* <p>
* When {@code duration} is zero, elements will be evicted immediately after
* being loaded into the cache. This has the same effect as invoking
* {@link #maximumSize maximumSize}{@code (0)}. It can be useful in testing,
* or to disable caching temporarily without a code change.
*
* <p>
* Expired entries may be counted by {@link com.google.common.cache.Cache#size Cache.size()}, but will never be
* visible to read or write operations. Expired entries are currently
* cleaned up during write operations, or during occasional read operations
* in the absense of writes; though this behavior may change in the future.
*
* @param duration the length of time after an entry is last accessed that
* it should be automatically removed
* @param unit the unit that {@code duration} is expressed in
* @throws IllegalArgumentException if {@code duration} is negative
* @throws IllegalStateException if the time to idle or time to live was
* already set
*/
public SafeCacheBuilder<K, V> expireAfterAccess(long duration, TimeUnit unit) {
builder.expireAfterAccess(duration, unit);
return this;
}
/**
* Specifies that each entry should be automatically removed from the cache
* once a fixed duration has elapsed after the entry's creation, or the most
* recent replacement of its value.
*
* <p>
* When {@code duration} is zero, elements will be evicted immediately after
* being loaded into the cache. This has the same effect as invoking
* {@link #maximumSize maximumSize}{@code (0)}. It can be useful in testing,
* or to disable caching temporarily without a code change.
*
* <p>
* Expired entries may be counted by {@link com.google.common.cache.Cache#size Cache.size()}, but will never be
* visible to read or write operations. Expired entries are currently
* cleaned up during write operations, or during occasional read operations
* in the absense of writes; though this behavior may change in the future.
*
* @param duration the length of time after an entry is created that it
* should be automatically removed
* @param unit the unit that {@code duration} is expressed in
* @throws IllegalArgumentException if {@code duration} is negative
* @throws IllegalStateException if the time to live or time to idle was
* already set
*/
public SafeCacheBuilder<K, V> expireAfterWrite(long duration, TimeUnit unit) {
builder.expireAfterWrite(duration, unit);
return this;
}
/**
* Sets the minimum total size for the internal hash tables. For example, if
* the initial capacity is {@code 60}, and the concurrency level is
* {@code 8}, then eight segments are created, each having a hash table of
* size eight. Providing a large enough estimate at construction time avoids
* the need for expensive resizing operations later, but setting this value
* unnecessarily high wastes memory.
*
* @throws IllegalArgumentException if {@code initialCapacity} is negative
* @throws IllegalStateException if an initial capacity was already set
*/
public SafeCacheBuilder<K, V> initialCapacity(int initialCapacity) {
builder.initialCapacity(initialCapacity);
return this;
}
/**
* Specifies the maximum number of entries the cache may contain. Note that
* the cache <b>may evict an entry before this limit is exceeded</b>. As the
* cache size grows close to the maximum, the cache evicts entries that are
* less likely to be used again. For example, the cache may evict an entry
* because it hasn't been used recently or very often.
*
* <p>
* When {@code size} is zero, elements will be evicted immediately after
* being loaded into the cache. This has the same effect as invoking
* {@link #expireAfterWrite expireAfterWrite}{@code (0, unit)} or
* {@link #expireAfterAccess expireAfterAccess}{@code (0,
* unit)}. It can be useful in testing, or to disable caching temporarily
* without a code change.
*
* @param size the maximum size of the cache
* @throws IllegalArgumentException if {@code size} is negative
* @throws IllegalStateException if a maximum size was already set
*/
public SafeCacheBuilder<K, V> maximumSize(int size) {
builder.maximumSize(size);
return this;
}
/**
* Specifies a listener instance, which all caches built using this
* {@code CacheBuilder} will notify each time an entry is removed from the
* cache by any means.
*
* <p>
* Each cache built by this {@code CacheBuilder} after this method is called
* invokes the supplied listener after removing an element for any reason
* (see removal causes in {@link com.google.common.cache.RemovalCause RemovalCause}). It will invoke the listener
* during invocations of any of that cache's public methods (even read-only
* methods).
*
* <p>
* <b>Important note:</b> Instead of returning <em>this</em> as a
* {@code CacheBuilder} instance, this method returns
* {@code CacheBuilder<K1, V1>}. From this point on, either the original
* reference or the returned reference may be used to complete configuration
* and build the cache, but only the "generic" one is type-safe. That is, it
* will properly prevent you from building caches whose key or value types
* are incompatible with the types accepted by the listener already
* provided; the {@code CacheBuilder} type cannot do this. For best results,
* simply use the standard method-chaining idiom, as illustrated in the
* documentation at top, configuring a {@code CacheBuilder} and building
* your {@link com.google.common.cache.Cache Cache} all in a single statement.
*
* <p>
* <b>Warning:</b> if you ignore the above advice, and use this
* {@code CacheBuilder} to build a cache whose key or value type is
* incompatible with the listener, you will likely experience a
* {@link ClassCastException} at some <i>undefined</i> point in the future.
*
* @throws IllegalStateException if a removal listener was already set
*/
@SuppressWarnings("unchecked")
public <K1 extends K, V1 extends V> SafeCacheBuilder<K1, V1> removalListener(RemovalListener<? super K1, ? super V1> listener) {
builder.removalListener(listener);
return (SafeCacheBuilder<K1, V1>) this;
}
/**
* Specifies a nanosecond-precision time source for use in determining when
* entries should be expired. By default, {@link System#nanoTime} is used.
*
* <p>
* The primary intent of this method is to facilitate testing of caches
* which have been configured with {@link #expireAfterWrite} or
* {@link #expireAfterAccess}.
*
* @throws IllegalStateException if a ticker was already set
*/
public SafeCacheBuilder<K, V> ticker(Ticker ticker) {
builder.ticker(ticker);
return this;
}
/**
* Specifies that each value (not key) stored in the cache should be wrapped
* in a {@link java.lang.ref.SoftReference SoftReference} (by default, strong references are used).
* Softly-referenced objects will be garbage-collected in a <i>globally</i>
* least-recently-used manner, in response to memory demand.
*
* <p>
* <b>Warning:</b> in most circumstances it is better to set a per-cache
* {@linkplain #maximumSize maximum size} instead of using soft references.
* You should only use this method if you are well familiar with the
* practical consequences of soft references.
*
* <p>
* <b>Note:</b> when this method is used, the resulting cache will use
* identity ({@code ==}) comparison to determine equality of values.
*
* @throws IllegalStateException if the value strength was already set
*/
public SafeCacheBuilder<K, V> softValues() {
builder.softValues();
return this;
}
/**
* Specifies that each key (not value) stored in the cache should be wrapped
* in a {@link java.lang.ref.WeakReference WeakReference} (by default, strong references are used).
*
* <p>
* <b>Warning:</b> when this method is used, the resulting cache will use
* identity ({@code ==}) comparison to determine equality of keys.
*
* @throws IllegalStateException if the key strength was already set
*/
public SafeCacheBuilder<K, V> weakKeys() {
builder.weakKeys();
return this;
}
/**
* Specifies that each value (not key) stored in the cache should be wrapped
* in a {@link java.lang.ref.WeakReference WeakReference} (by default, strong references are used).
*
* <p>
* Weak values will be garbage collected once they are weakly reachable.
* This makes them a poor candidate for caching; consider
* {@link #softValues} instead.
*
* <p>
* <b>Note:</b> when this method is used, the resulting cache will use
* identity ({@code ==}) comparison to determine equality of values.
*
* @throws IllegalStateException if the value strength was already set
*/
public SafeCacheBuilder<K, V> weakValues() {
builder.weakValues();
return this;
}
/**
* Returns the cache wrapped as a ConcurrentMap.
* <>
* We can't return the direct Cache instance as it changed in Guava 13.
* @return The cache as a map.
*/
@SuppressWarnings("unchecked")
public <K1 extends K, V1 extends V> ConcurrentMap<K1, V1> build(CacheLoader<? super K1, V1> loader) {
Object cache = null;
if (BUILD_METHOD == null) {
try {
BUILD_METHOD = builder.getClass().getDeclaredMethod("build", CacheLoader.class);
BUILD_METHOD.setAccessible(true);
} catch (Exception e) {
throw new FieldAccessException("Unable to find CacheBuilder.build(CacheLoader)", e);
}
}
// Attempt to build the Cache
try {
cache = BUILD_METHOD.invoke(builder, loader);
} catch (Exception e) {
throw new FieldAccessException("Unable to invoke " + BUILD_METHOD + " on " + builder, e);
}
if (AS_MAP_METHOD == null) {
try {
AS_MAP_METHOD = cache.getClass().getMethod("asMap");
AS_MAP_METHOD.setAccessible(true);
} catch (Exception e) {
throw new FieldAccessException("Unable to find Cache.asMap() in " + cache, e);
}
}
// Retrieve it as a map
try {
return (ConcurrentMap<K1, V1>) AS_MAP_METHOD.invoke(cache);
} catch (Exception e) {
throw new FieldAccessException("Unable to invoke " + AS_MAP_METHOD + " on " + cache, e);
}
}
}