DecayingHashSet (Javadocs [I2P+ 2.13.0+]

java.lang.Object
- net.i2p.router.util.DecayingBloomFilter
- - net.i2p.router.util.DecayingHashSet

```
public class DecayingHashSet
extends DecayingBloomFilter
```
Double-buffered hash set with time-based decay for efficient data management.
Extends DecayingBloomFilter to provide dual-buffered hash sets with automatic decay switching between active and previous buffers. Optimized for high-throughput scenarios with frequent insertions and periodic cleanup operations.
Memory usage analysis shows significant optimization potential:
- 32 bytes, peak 10 entries in 1m (320 on fast routers)
- 4 bytes, peak 150 entries in 10s (1600 on fast routers)
- 8 bytes, peak 1K entries in 2m (36K on fast routers)
- 16 bytes, peak 15K entries in 10m (15K on fast routers)
Performance characteristics:
- Zero false positive rate for ≤8 byte keys (lossy hash for larger keys)
- 5.4E-20 false positive rate for larger keys
- Twice as fast as DBF in benchmarks
- Space-proportional traffic handling
Uses read/write locks with SimpleTimer2 for thread safety and efficient buffer switching without synchronization overhead.

Field Summary
- Fields inherited from class net.i2p.router.util.DecayingBloomFilter
  _context, _currentDuplicates, _decayEvent, _durationMs, _entryBytes, _keepDecaying, _log, _name, _reorganizeLock

Constructor Summary

Constructors
Constructor and Description
`DecayingHashSet(I2PAppContext context, int durationMs, int entryBytes)` Create a double-buffered hash set that will decay its entries over time.
`DecayingHashSet(I2PAppContext context, int durationMs, int entryBytes, String name)` Decaying hash set with a custom name.

Method Summary

All Methods Instance Methods Concrete Methods
Modifier and Type	Method and Description
`boolean`	`add(byte[] entry, int off, int len)` Add the entry, returning whether it was a duplicate.
`boolean`	`add(long entry)` Add the long entry, returning whether it was a duplicate.
`void`	`clear()` Clear all filters and reset counts
`protected void`	`decay()` Decay the filter, moving the current buffer to the previous.
`double`	`getFalsePositiveRate()` Stubbed rate; only used for logging elsewhere.
`int`	`getInsertedCount()` Unsynchronized but only used for logging elsewhere.
`boolean`	`isKnown(long entry)` Check whether the entry is already known, without adding it.
`void`	`stopDecaying()` Super doesn't call clear, but neither do the users, so it seems like we should here.

Methods inherited from class net.i2p.router.util.DecayingBloomFilter
add, getCurrentDuplicateCount, getReadLock, getWriteLock, releaseReadLock, releaseWriteLock

Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

- Constructor Detail
  - DecayingHashSet
```
public DecayingHashSet(I2PAppContext context,
                       int durationMs,
                       int entryBytes)
```
    Create a double-buffered hash set that will decay its entries over time.
    Parameters:
    durationMs - entries last for at least this long, but no more than twice this long
    entryBytes - how large are the entries to be added? 1 to 32 bytes
  - DecayingHashSet
```
public DecayingHashSet(I2PAppContext context,
                       int durationMs,
                       int entryBytes,
                       String name)
```
    Decaying hash set with a custom name.
    Parameters:
    name - just for logging / debugging / stats
- Method Detail
  - add
```
public boolean add(byte[] entry,
                   int off,
                   int len)
```
    Add the entry, returning whether it was a duplicate.
    Overrides:
    add in class DecayingBloomFilter
    Parameters:
    entry - the entry data
    off - the offset
    len - the length
    Returns:
    true if the entry added is a duplicate
  - add
```
public boolean add(long entry)
```
    Add the long entry, returning whether it was a duplicate.
    Overrides:
    add in class DecayingBloomFilter
    Parameters:
    entry - the long value to add
    Returns:
    true if the entry added is a duplicate. the number of low order bits used is determined by the entryBytes parameter used on creation of the filter.
  - clear
```
public void clear()
```
    Description copied from class: DecayingBloomFilter
    Clear all filters and reset counts
    Overrides:
    clear in class DecayingBloomFilter
  - decay
```
protected void decay()
```
    Description copied from class: DecayingBloomFilter
    Decay the filter, moving the current buffer to the previous.
    Overrides:
    decay in class DecayingBloomFilter
  - getFalsePositiveRate
```
public double getFalsePositiveRate()
```
    Stubbed rate; only used for logging elsewhere.
    Overrides:
    getFalsePositiveRate in class DecayingBloomFilter
    Returns:
    the false positive rate
  - getInsertedCount
```
public int getInsertedCount()
```
    Unsynchronized but only used for logging elsewhere.
    Overrides:
    getInsertedCount in class DecayingBloomFilter
  - isKnown
```
public boolean isKnown(long entry)
```
    Check whether the entry is already known, without adding it.
    Overrides:
    isKnown in class DecayingBloomFilter
    Parameters:
    entry - the long value to check
    Returns:
    true if the entry is already known. this does NOT add the entry however.
  - stopDecaying
```
public void stopDecaying()
```
    Super doesn't call clear, but neither do the users, so it seems like we should here.
    Overrides:
    stopDecaying in class DecayingBloomFilter

Class DecayingHashSet

Field Summary

Fields inherited from class net.i2p.router.util.DecayingBloomFilter

Constructor Summary

Method Summary

Methods inherited from class net.i2p.router.util.DecayingBloomFilter

Methods inherited from class java.lang.Object

Constructor Detail

DecayingHashSet

DecayingHashSet

Method Detail

add

add

clear

decay

getFalsePositiveRate

getInsertedCount

isKnown

stopDecaying