org.codehaus.groovy.runtime.metaclass
[Java] 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.

Authors:

Adapted from ConcurrentHashMap (Doug Lea)

adapted by the Groovy community

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.

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.

barrierLock

protected final MemoryAwareConcurrentReadMap.BarrierLock barrierLock

Lock used only for its memory effects.

count

protected int count

The total number of mappings in the hash table.

lastWrite

protected Object lastWrite

field written to only to guarantee lock ordering.

loadFactor

protected float loadFactor

The load factor for the hash table.

serial:

table

protected Entry[] table

The hash table data.

threshold

protected int threshold

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

serial:

MemoryAwareConcurrentReadMap

public def MemoryAwareConcurrentReadMap(int initialCapacity, float loadFactor)

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

throws:

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

Parameters:

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

loadFactor - the load factor of the ConcurrentReaderHashMap

MemoryAwareConcurrentReadMap

public def MemoryAwareConcurrentReadMap(int initialCapacity)

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

throws:

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

Parameters:

initialCapacity - the initial capacity of the ConcurrentReaderHashMap.

MemoryAwareConcurrentReadMap

public def MemoryAwareConcurrentReadMap()

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

clear

public void clear()

Removes all mappings from this map.

eq

protected boolean eq(Object x, Object y)

Check for referential equality, null allowed

get

public Object get(Object key)

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

Throws:

NullPointerException if the key is null.

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.

See Also:

put(Object, Object)

getTableForReading

protected final 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

isEmpty

public boolean isEmpty()

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

Returns:

true if this map contains no key-value mappings.

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.

Throws:

NullPointerException if the key or value is null.

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.

See Also:

get(Object)

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.

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.

Throws:

NullPointerException if the key is null.

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.

size

public int size()

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

Returns:

the number of key-value mappings in this map.

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.

sremove

protected Object sremove(Object key, int hash)

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

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