标签：form cat 就是 err 分享 lca table max ash
写了上面一篇，看了点eventbus相关的guava代码后，发现里面用到了很多其他guava包里的方法，所以顺着看一下，比如之前用到的map都是guava自己的
Multimap：可以包含有几个重复Key的value，你可以put进入多个不同value但是相同的key，但是又不是让后面覆盖前面的内容。
Table：二维矩阵类似，有需要这类结构可以参考
Hash：还有一堆已经实现好了的哈希方法，如果有需要可以直接用
有些代码也可以从中参考
对于Cache首先写一个例子，一般缓存肯定要考虑的是怎么存，存多久，怎么过期，初始大小，最大大小等等
LoadingCache<String, String> cache = CacheBuilder.newBuilder() .expireAfterWrite(1000, TimeUnit.MILLISECONDS) .expireAfterAccess(1000, TimeUnit.MILLISECONDS) .concurrencyLevel(8) .initialCapacity(100) .maximumSize(100) .weakKeys() .weakValues() .build(new CacheLoader<String, String>() { @Override public String load(String key) throws Exception { return "test"; } });
其中参数大部分一看名字就知道，这里我觉得比较特殊的是这个，看注释就明白了
@GwtIncompatible // java.lang.ref.WeakReference public CacheBuilder<K, V> weakKeys() { return setKeyStrength(Strength.WEAK); }
WEAK { @Override <K, V> ValueReference<K, V> referenceValue( Segment<K, V> segment, ReferenceEntry<K, V> entry, V value, int weight) { return (weight == 1) ? new WeakValueReference<K, V>(segment.valueReferenceQueue, value, entry) : new WeightedWeakValueReference<K, V>( segment.valueReferenceQueue, value, entry, weight); } @Override Equivalence<Object> defaultEquivalence() { return Equivalence.identity(); } };
put放入元素，跟一般的没多大区别，就是计算下hash，找到对应的index放进去，就是map的一般原理
@Override public V put(K key, V value) { checkNotNull(key); checkNotNull(value); int hash = hash(key); return segmentFor(hash).put(key, hash, value, false); }
来看具体的put，起始也比较好懂
@Nullable V put(K key, int hash, V value, boolean onlyIfAbsent) { lock(); try { long now = map.ticker.read(); preWriteCleanup(now); int newCount = this.count + 1; if (newCount > this.threshold) { // ensure capacity expand(); newCount = this.count + 1; } AtomicReferenceArray<ReferenceEntry<K, V>> table = this.table; int index = hash & (table.length() - 1); ReferenceEntry<K, V> first = table.get(index); // Look for an existing entry. for (ReferenceEntry<K, V> e = first; e != null; e = e.getNext()) { K entryKey = e.getKey(); if (e.getHash() == hash && entryKey != null && map.keyEquivalence.equivalent(key, entryKey)) { // We found an existing entry. ValueReference<K, V> valueReference = e.getValueReference(); V entryValue = valueReference.get(); if (entryValue == null) { ++modCount; if (valueReference.isActive()) { enqueueNotification( key, hash, entryValue, valueReference.getWeight(), RemovalCause.COLLECTED); setValue(e, key, value, now); newCount = this.count; // count remains unchanged } else { setValue(e, key, value, now); newCount = this.count + 1; } this.count = newCount; // write-volatile evictEntries(e); return null; } else if (onlyIfAbsent) { // Mimic // "if (!map.containsKey(key)) ... // else return map.get(key); recordLockedRead(e, now); return entryValue; } else { // clobber existing entry, count remains unchanged ++modCount; enqueueNotification( key, hash, entryValue, valueReference.getWeight(), RemovalCause.REPLACED); setValue(e, key, value, now); evictEntries(e); return entryValue; } } } // Create a new entry. ++modCount; ReferenceEntry<K, V> newEntry = newEntry(key, hash, first); setValue(newEntry, key, value, now); table.set(index, newEntry); newCount = this.count + 1; this.count = newCount; // write-volatile evictEntries(newEntry); return null; } finally { unlock(); postWriteCleanup(); } }
void runLockedCleanup(long now) { if (tryLock()) { try { drainReferenceQueues(); expireEntries(now); // calls drainRecencyQueue readCount.set(0); } finally { unlock(); } } }
再看下get
@Override public @Nullable V get(@Nullable Object key) { if (key == null) { return null; } int hash = hash(key); return segmentFor(hash).get(key, hash); }
@Nullable V get(Object key, int hash) { try { if (count != 0) { // read-volatile long now = map.ticker.read(); ReferenceEntry<K, V> e = getLiveEntry(key, hash, now); if (e == null) { return null; } V value = e.getValueReference().get(); if (value != null) { recordRead(e, now); return scheduleRefresh(e, e.getKey(), hash, value, now, map.defaultLoader); } tryDrainReferenceQueues(); } return null; } finally { postReadCleanup(); } }
/** * Records the relative order in which this read was performed by adding {@code entry} to the * recency queue. At write-time, or when the queue is full past the threshold, the queue will be * drained and the entries therein processed. * * <p>Note: locked reads should use {@link #recordLockedRead}. */ void recordRead(ReferenceEntry<K, V> entry, long now) { if (map.recordsAccess()) { entry.setAccessTime(now); } recencyQueue.add(entry); }
标签：form cat 就是 err 分享 lca table max ash
原文地址：https://www.cnblogs.com/it-worker365/p/9946588.html
