DecayingBloomFilter (Javadocs [I2P+ 2.13.0+]

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

Direct Known Subclasses:
DecayingHashSet
```
public class DecayingBloomFilter
extends Object
```
Time-decaying Bloom filter series for efficient data management.
Provides a series of Bloom filters with automatic time-based decay to handle time-sensitive data with minimal false positive rates. Uses fixed-size buffers with periodic switching to maintain consistent memory usage while allowing high-throughput operations.
Optimized for scenarios requiring hundreds of entries per second with virtually no false positive rate. Memory usage is carefully controlled through configurable filter parameters and buffer sizes.
Performance characteristics:
- Configurable m and k parameters for optimal false positive rates
- Automatic buffer switching and decay operations
- Thread-safe with read/write lock coordination
- Comprehensive statistics tracking and performance monitoring
Suitable for high-throughput applications like message validation, tunnel IV filtering, and router message processing where memory efficiency and low false positive rates are critical.
See Also:
DecayingHashSet, BloomFilterIVValidator

Field Summary

Fields
Modifier and Type	Field and Description
`protected I2PAppContext`	`_context` The I2P app context
`protected AtomicLong`	`_currentDuplicates` Counter for current duplicates
`protected SimpleTimer2.TimedEvent`	`_decayEvent` The decay timer event
`protected int`	`_durationMs` Duration of each filter in ms
`protected int`	`_entryBytes` Size of entries in bytes
`protected boolean`	`_keepDecaying` Whether decay is still running
`protected Log`	`_log` The logger
`protected String`	`_name` just for logging
`protected ReentrantReadWriteLock`	`_reorganizeLock` synchronize against this lock when switching double buffers

Constructor Summary

Constructors
Modifier	Constructor and Description
	`DecayingBloomFilter(I2PAppContext context, int durationMs, int entryBytes)` Create a bloom filter that will decay its entries over time.
	`DecayingBloomFilter(I2PAppContext context, int durationMs, int entryBytes, String name)` Uses default m of 23, memory usage is 2 MB.
	`DecayingBloomFilter(I2PAppContext context, int durationMs, int entryBytes, String name, int m)` Memory usage is 2 * (2m) bits or 2(m-2) bytes.
`protected`	`DecayingBloomFilter(int durationMs, int entryBytes, String name, I2PAppContext context)` Only for extension by DecayingHashSet

Method Summary

All Methods Instance Methods Concrete Methods
Modifier and Type	Method and Description
`boolean`	`add(byte[] entry)` Add a byte array entry to the filter
`boolean`	`add(byte[] entry, int off, int len)` Add a byte array entry at the specified offset and length
`boolean`	`add(long entry)` Add a long entry to the filter.
`void`	`clear()` Clear all filters and reset counts
`protected void`	`decay()` decay.
`long`	`getCurrentDuplicateCount()`
`double`	`getFalsePositiveRate()` Get the false positive rate
`int`	`getInsertedCount()` unsynchronized but only used for logging elsewhere
`protected void`	`getReadLock()` Acquire the read lock
`protected boolean`	`getWriteLock()` Acquire the write lock
`boolean`	`isKnown(long entry)` Check if an entry is already known without adding it
`protected void`	`releaseReadLock()` Release the read lock
`protected void`	`releaseWriteLock()` Release the write lock
`void`	`stopDecaying()` Stop the decay process

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

- Field Detail
  - _context
```
protected final I2PAppContext _context
```
    The I2P app context
  - _currentDuplicates
```
protected final AtomicLong _currentDuplicates
```
    Counter for current duplicates
  - _decayEvent
```
protected final SimpleTimer2.TimedEvent _decayEvent
```
    The decay timer event
  - _durationMs
```
protected final int _durationMs
```
    Duration of each filter in ms
  - _entryBytes
```
protected final int _entryBytes
```
    Size of entries in bytes
  - _keepDecaying
```
protected volatile boolean _keepDecaying
```
    Whether decay is still running
  - _log
```
protected final Log _log
```
    The logger
  - _name
```
protected final String _name
```
    just for logging
  - _reorganizeLock
```
protected final ReentrantReadWriteLock _reorganizeLock
```
    synchronize against this lock when switching double buffers
- Constructor Detail
  - DecayingBloomFilter
```
public DecayingBloomFilter(I2PAppContext context,
                           int durationMs,
                           int entryBytes)
```
    Create a bloom filter that will decay its entries over time. Uses default m of 23, memory usage is 2 MB.
    Parameters:
    context - the I2P app context
    durationMs - entries last for at least this long, but no more than twice this long
    entryBytes - how large are the entries to be added? if this is less than 32 bytes, the entries added will be expanded by concatenating their XORing against with sufficient random values.
  - DecayingBloomFilter
```
public DecayingBloomFilter(I2PAppContext context,
                           int durationMs,
                           int entryBytes,
                           String name)
```
    Uses default m of 23, memory usage is 2 MB.
    Parameters:
    context - the I2P app context
    durationMs - entries last for at least this long
    entryBytes - how large are the entries
    name - just for logging / debugging / stats
  - DecayingBloomFilter
```
public DecayingBloomFilter(I2PAppContext context,
                           int durationMs,
                           int entryBytes,
                           String name,
                           int m)
```
    Memory usage is 2 * (2**m) bits or 2**(m-2) bytes.
    Parameters:
    context - the I2P app context
    durationMs - entries last for at least this long
    entryBytes - how large are the entries
    name - filter name for logging
    m - filter size exponent, max is 29
  - DecayingBloomFilter
```
protected DecayingBloomFilter(int durationMs,
                              int entryBytes,
                              String name,
                              I2PAppContext context)
```
    Only for extension by DecayingHashSet
    Parameters:
    durationMs - entries last for at least this long
    entryBytes - how large are the entries
    name - filter name for logging
    context - the I2P app context
- Method Detail
  - add
```
public boolean add(byte[] entry)
```
    Add a byte array entry to the filter
    Parameters:
    entry - the entry to add
    Returns:
    true if the entry added is a duplicate
  - add
```
public boolean add(byte[] entry,
                   int off,
                   int len)
```
    Add a byte array entry at the specified offset and length
    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 a long entry to the filter. The number of low order bits used is determined by the entryBytes parameter used on creation of the filter.
    Parameters:
    entry - the long value to add
    Returns:
    true if the entry added is a duplicate
  - clear
```
public void clear()
```
    Clear all filters and reset counts
  - decay
```
protected void decay()
```
    decay.
  - getCurrentDuplicateCount
```
public long getCurrentDuplicateCount()
```
    Returns:
    the current duplicate count
  - getFalsePositiveRate
```
public double getFalsePositiveRate()
```
    Get the false positive rate
    Returns:
    the false positive rate
  - getInsertedCount
```
public int getInsertedCount()
```
    unsynchronized but only used for logging elsewhere
  - getReadLock
```
protected void getReadLock()
```
    Acquire the read lock
  - getWriteLock
```
protected boolean getWriteLock()
```
    Acquire the write lock
    Returns:
    true if the lock was acquired
  - isKnown
```
public boolean isKnown(long entry)
```
    Check if an entry is already known without adding it
    Parameters:
    entry - the long value to check
    Returns:
    true if the entry is already known. this does NOT add the entry however.
  - releaseReadLock
```
protected void releaseReadLock()
```
    Release the read lock
  - releaseWriteLock
```
protected void releaseWriteLock()
```
    Release the write lock
  - stopDecaying
```
public void stopDecaying()
```
    Stop the decay process

Class DecayingBloomFilter

Field Summary

Constructor Summary

Method Summary

Methods inherited from class java.lang.Object

Field Detail

_context

_currentDuplicates

_decayEvent

_durationMs

_entryBytes

_keepDecaying

_log

_name

_reorganizeLock

Constructor Detail

DecayingBloomFilter

DecayingBloomFilter

DecayingBloomFilter

DecayingBloomFilter

Method Detail

add

add

add

clear

decay

getCurrentDuplicateCount

getFalsePositiveRate

getInsertedCount

getReadLock

getWriteLock

isKnown

releaseReadLock

releaseWriteLock

stopDecaying