Cache (milky-common 1.0.1 API)

java.lang.Object
- cn.sliew.milky.common.cache.local.Cache<K,V>

类型参数:

K - The type of the keys

V - The type of the values
```
public class Cache<K,V>
extends Object
```
A simple concurrent cache.
Cache is a simple concurrent cache that supports time-based and weight-based evictions, with notifications for all evictions. The design goals for this cache were simplicity and read performance. This means that we are willing to accept reduced write performance in exchange for easy-to-understand code. Cache statistics for hits, misses and evictions are exposed.
The design of the cache is relatively simple. The cache is segmented into 256 segments which are backed by HashMaps. Each segment is protected by a re-entrant read/write lock. The read/write locks permit multiple concurrent readers without contention, and the segments gives us write throughput without impacting readers (so readers are blocked only if they are reading a segment that a writer is writing to).
The LRU functionality is backed by a single doubly-linked list chaining the entries in order of insertion. This LRU list is protected by a lock that serializes all writes to it. There are opportunities for improvements here if write throughput is a concern.
1. LRU list mutations could be inserted into a blocking queue that a single thread is reading from and applying to the LRU list.
2. Promotions could be deferred for entries that were "recently" promoted.
3. Locks on the list could be taken per node being modified instead of globally.
Evictions only occur after a mutation to the cache (meaning an entry promotion, a cache insertion, or a manual invalidation) or an explicit call to refresh().

嵌套类概要

嵌套类
限定符和类型类和说明

static class Cache.CacheStats

嵌套类
限定符和类型	类和说明
`static class`	`Cache.CacheStats`

字段概要

字段
限定符和类型字段和说明

static int NUMBER_OF_SEGMENTS

字段
限定符和类型	字段和说明
`static int`	`NUMBER_OF_SEGMENTS`

方法概要

所有方法实例方法具体方法
限定符和类型	方法和说明
`V`	`computeIfAbsent(K key, CacheLoader<K,V> loader)` If the specified key is not already associated with a value (or is mapped to null), attempts to compute its value using the given mapping function and enters it into this map unless null.
`int`	`count()` The number of entries in the cache.
`V`	`get(K key)` Returns the value to which the specified key is mapped, or null if this map contains no mapping for the key.
`void`	`invalidate(K key)` Invalidate the association for the specified key.
`void`	`invalidate(K key, V value)` Invalidate the entry for the specified key and value.
`void`	`invalidateAll()` Invalidate all cache entries.
`Iterable<K>`	`keys()` An LRU sequencing of the keys in the cache that supports removal.
`protected long`	`now()` The relative time used to track time-based evictions.
`void`	`put(K key, V value)` Associates the specified value with the specified key in this map.
`void`	`refresh()` Force any outstanding size-based and time-based evictions to occur
`Cache.CacheStats`	`stats()` The cache statistics tracking hits, misses and evictions.
`Iterable<V>`	`values()` An LRU sequencing of the values in the cache.
`long`	`weight()` The weight of the entries in the cache.

从类继承的方法 java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

- 字段详细资料
  - NUMBER_OF_SEGMENTS
```
public static final int NUMBER_OF_SEGMENTS
```
    另请参阅:
    
    常量字段值
- 方法详细资料
  - now
```
protected long now()
```
    The relative time used to track time-based evictions.
    
    返回:
    
    the current relative time
  - get
```
public V get(K key)
```
    Returns the value to which the specified key is mapped, or null if this map contains no mapping for the key.
    
    参数:
    
    key - the key whose associated value is to be returned
    
    返回:
    
    the value to which the specified key is mapped, or null if this map contains no mapping for the key
  - computeIfAbsent
```
public V computeIfAbsent(K key,
                         CacheLoader<K,V> loader)
                  throws ExecutionException
```
    If the specified key is not already associated with a value (or is mapped to null), attempts to compute its value using the given mapping function and enters it into this map unless null. The load method for a given key will be invoked at most once.
    Use of different CacheLoader implementations on the same key concurrently may result in only the first loader function being called and the second will be returned the result provided by the first including any exceptions thrown during the execution of the first.
    
    参数:
    
    key - the key whose associated value is to be returned or computed for if non-existent
    
    loader - the function to compute a value given a key
    
    返回:
    
    the current (existing or computed) non-null value associated with the specified key
    
    抛出:
    
    ExecutionException - thrown if loader throws an exception or returns a null value
  - put
```
public void put(K key,
                V value)
```
    Associates the specified value with the specified key in this map. If the map previously contained a mapping for the key, the old value is replaced.
    
    参数:
    
    key - key with which the specified value is to be associated
    
    value - value to be associated with the specified key
  - invalidate
```
public void invalidate(K key)
```
    Invalidate the association for the specified key. A removal notification will be issued for invalidated entries with RemovalNotification.RemovalReason INVALIDATED.
    
    参数:
    
    key - the key whose mapping is to be invalidated from the cache
  - invalidate
```
public void invalidate(K key,
                       V value)
```
    Invalidate the entry for the specified key and value. If the value provided is not equal to the value in the cache, no removal will occur. A removal notification will be issued for invalidated entries with RemovalNotification.RemovalReason INVALIDATED.
    
    参数:
    
    key - the key whose mapping is to be invalidated from the cache
    
    value - the expected value that should be associated with the key
  - invalidateAll
```
public void invalidateAll()
```
    Invalidate all cache entries. A removal notification will be issued for invalidated entries with RemovalNotification.RemovalReason INVALIDATED.
  - refresh
```
public void refresh()
```
    Force any outstanding size-based and time-based evictions to occur
  - count
```
public int count()
```
    The number of entries in the cache.
    
    返回:
    
    the number of entries in the cache
  - weight
```
public long weight()
```
    The weight of the entries in the cache.
    
    返回:
    
    the weight of the entries in the cache
  - keys
```
public Iterable<K> keys()
```
    An LRU sequencing of the keys in the cache that supports removal. This sequence is not protected from mutations to the cache (except for Iterator.remove(). The result of iteration under any other mutation is undefined.
    
    返回:
    
    an LRU-ordered Iterable over the keys in the cache
  - values
```
public Iterable<V> values()
```
    An LRU sequencing of the values in the cache. This sequence is not protected from mutations to the cache (except for Iterator.remove(). The result of iteration under any other mutation is undefined.
    
    返回:
    
    an LRU-ordered Iterable over the values in the cache
  - stats
```
public Cache.CacheStats stats()
```
    The cache statistics tracking hits, misses and evictions. These are taken on a best-effort basis meaning that they could be out-of-date mid-flight.
    
    返回:
    
    the current cache statistics

类 Cache<K,V>

嵌套类概要

字段概要

方法概要

从类继承的方法 java.lang.Object

字段详细资料

NUMBER_OF_SEGMENTS

方法详细资料

now

get

computeIfAbsent

put

invalidate

invalidate

invalidateAll

refresh

count

weight

keys

values

stats