org.codehaus.groovy.runtime.metaclass

Class MemoryAwareConcurrentReadMap

java.lang.Object

org.codehaus.groovy.runtime.metaclass.MemoryAwareConcurrentReadMap

public class MemoryAwareConcurrentReadMap
extends Object

This Map is a stripped down version of ConcurrentReaderHashMap with small modifications here and there. It is no full Map, it does have put/get/remove, but no iterators. This map is intended to hold values and keys as SoftReference. If one of value or key are removed, so will be complete entry. This map will not use the equals method to compare keys, think of it as a IdentityHashMap with features of concurrency and memory aware caching. As ConcurrentReaderHashMap also does this implementation prefer read operations and tries not to lock if possible. SoftReferenced values are only removed from the map if the map goes into a synchronization block on this. This may affect reads, but only in rare cases.

Author:

Adapted from ConcurrentHashMap (Doug Lea), adapted by the Groovy community

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
protected static class	MemoryAwareConcurrentReadMap.BarrierLock A Serializable class for barrier lock

Field Summary

Fields

Modifier and Type	Field and Description
protected MemoryAwareConcurrentReadMap.BarrierLock	barrierLock Lock used only for its memory effects.
protected int	count The total number of mappings in the hash table.
static int	DEFAULT_INITIAL_CAPACITY The default initial number of table slots for this table (32).
static float	DEFAULT_LOAD_FACTOR The default load factor for this table (1.0).
protected Object	lastWrite field written to only to guarantee lock ordering.
protected float	loadFactor The load factor for the hash table.
protected org.codehaus.groovy.runtime.metaclass.MemoryAwareConcurrentReadMap.Entry[]	table The hash table data.
protected int	threshold The table is rehashed when its size exceeds this threshold.

Constructor Summary

Constructors

Constructor and Description
MemoryAwareConcurrentReadMap() Constructs a new, empty map with a default initial capacity and load factor.
MemoryAwareConcurrentReadMap(int initialCapacity) Constructs a new, empty map with the specified initial capacity and default load factor.
MemoryAwareConcurrentReadMap(int initialCapacity, float loadFactor) Constructs a new, empty map with the specified initial capacity and the specified load factor.

Method Summary

Methods

Modifier and Type	Method and Description
void	clear() Removes all mappings from this map.
protected boolean	eq(Object x, Object y) Check for referential equality, null allowed
Object	get(Object key) Returns the value to which the specified key is mapped in this table.
protected org.codehaus.groovy.runtime.metaclass.MemoryAwareConcurrentReadMap.Entry[]	getTableForReading() Get ref to table; the reference and the cells it accesses will be at least as fresh as from last use of barrierLock
boolean	isEmpty() Returns true if this map contains no key-value mappings.
Object	put(Object key, Object value) Maps the specified key to the specified value in this table.
protected void	recordModification(Object x) Force a memory synchronization that will cause all readers to see table.
protected void	rehash() Rehashes the contents of this map into a new table with a larger capacity.
Object	remove(Object key) Removes the key (and its corresponding value) from this table.
int	size() Returns the number of key-value mappings in this map.
protected Object	sput(Object key, Object value, int hash) Continuation of put(), called only when synch lock is held and interference has been detected.
protected Object	sremove(Object key, int hash) Continuation of remove(), called only when synch lock is held and interference has been detected.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

barrierLock

protected final MemoryAwareConcurrentReadMap.BarrierLock barrierLock

Lock used only for its memory effects.

lastWrite

protected transient Object lastWrite

field written to only to guarantee lock ordering.

DEFAULT_INITIAL_CAPACITY

public static final int DEFAULT_INITIAL_CAPACITY

The default initial number of table slots for this table (32). Used when not otherwise specified in constructor.

See Also:

Constant Field Values

DEFAULT_LOAD_FACTOR

public static final float DEFAULT_LOAD_FACTOR

The default load factor for this table (1.0). Used when not otherwise specified in constructor.

See Also:

Constant Field Values

table

protected transient org.codehaus.groovy.runtime.metaclass.MemoryAwareConcurrentReadMap.Entry[] table

The hash table data.

count

protected transient int count

The total number of mappings in the hash table.

threshold

protected int threshold

The table is rehashed when its size exceeds this threshold. (The value of this field is always (int)(capacity * loadFactor).)

loadFactor

protected float loadFactor

The load factor for the hash table.

Constructor Detail

MemoryAwareConcurrentReadMap

public MemoryAwareConcurrentReadMap(int initialCapacity,
                            float loadFactor)

Constructs a new, empty map with the specified initial capacity and the specified load factor.

Parameters:

initialCapacity - the initial capacity The actual initial capacity is rounded to the nearest power of two.

loadFactor - the load factor of the ConcurrentReaderHashMap

Throws:

IllegalArgumentException - if the initial maximum number of elements is less than zero, or if the load factor is non-positive.

MemoryAwareConcurrentReadMap

public MemoryAwareConcurrentReadMap(int initialCapacity)

Constructs a new, empty map with the specified initial capacity and default load factor.

Parameters:

initialCapacity - the initial capacity of the ConcurrentReaderHashMap.

Throws:

IllegalArgumentException - if the initial maximum number of elements is less than zero.

MemoryAwareConcurrentReadMap

public MemoryAwareConcurrentReadMap()

Constructs a new, empty map with a default initial capacity and load factor.

Method Detail

recordModification

protected final void recordModification(Object x)

Force a memory synchronization that will cause all readers to see table. Call only when already holding main synch lock.

getTableForReading

protected final org.codehaus.groovy.runtime.metaclass.MemoryAwareConcurrentReadMap.Entry[] getTableForReading()

Get ref to table; the reference and the cells it accesses will be at least as fresh as from last use of barrierLock

eq

protected boolean eq(Object x,
         Object y)

Check for referential equality, null allowed

size

public int size()

Returns the number of key-value mappings in this map.

Returns:

the number of key-value mappings in this map.

isEmpty

public boolean isEmpty()

Returns true if this map contains no key-value mappings.

Returns:

true if this map contains no key-value mappings.

get

public Object get(Object key)

Returns the value to which the specified key is mapped in this table.

Parameters:

key - a key in the table.

Returns:

the value to which the key is mapped in this table; null if the key is not mapped to any value in this table.

Throws:

NullPointerException - if the key is null.

See Also:

put(Object, Object)

put

public Object put(Object key,
         Object value)

Maps the specified key to the specified value in this table. Neither the key nor the value can be null.

The value can be retrieved by calling the get method with a key that is equal to the original key.

Parameters:

key - the table key.

value - the value.

Returns:

the previous value of the specified key in this table, or null if it did not have one.

Throws:

NullPointerException - if the key or value is null.

See Also:

get(Object)

sput

protected Object sput(Object key,
          Object value,
          int hash)

Continuation of put(), called only when synch lock is held and interference has been detected.

rehash

protected void rehash()

Rehashes the contents of this map into a new table with a larger capacity. This method is called automatically when the number of keys in this map exceeds its capacity and load factor.

remove

public Object remove(Object key)

Removes the key (and its corresponding value) from this table. This method does nothing if the key is not in the table.

Parameters:

key - the key that needs to be removed.

Returns:

the value to which the key had been mapped in this table, or null if the key did not have a mapping.

Throws:

NullPointerException - if the key is null.

sremove

protected Object sremove(Object key,
             int hash)

Continuation of remove(), called only when synch lock is held and interference has been detected.

clear

public void clear()

Removes all mappings from this map.