java.lang
Class ThreadLocal.ThreadLocalMap

java.lang.Object
  java.lang.ThreadLocal.ThreadLocalMap

Enclosing class:

ThreadLocal

static class ThreadLocal.ThreadLocalMap

extends Object

ThreadLocalMap is a customized hash map suitable only for maintaining thread local values. No operations are exported outside of the ThreadLocal class. The class is package private to allow declaration of fields in class Thread. To help deal with very large and long-lived usages, the hash table entries use WeakReferences for keys. However, since reference queues are not used, stale entries are guaranteed to be removed only when the table starts running out of space.

Nested Class Summary

private static class

ThreadLocal.ThreadLocalMap.Entry The entries in this hash map extend WeakReference, using its main ref field as the key (which is always a ThreadLocal object).

Field Summary

private static int	INITIAL_CAPACITY The initial capacity -- MUST be a power of two.
private int	size The number of entries in the table.
private ThreadLocal.ThreadLocalMap.Entry[]	table The table, resized as necessary.
private int	threshold The next size value at which to resize.

Constructor Summary

private	ThreadLocal.ThreadLocalMap(ThreadLocal.ThreadLocalMap parentMap) Construct a new map including all Inheritable ThreadLocals from given parent map.
(package private)	ThreadLocal.ThreadLocalMap(ThreadLocal firstKey, Object firstValue) Construct a new map initially containing (firstKey, firstValue).

Method Summary

private void	expungeStaleEntries() Expunge all stale entries in the table.
private void	expungeStaleEntry(int staleSlot) Expunge a stale entry by rehashing any possibly colliding entries lying between staleSlot and the next null slot.
private Object	get(ThreadLocal key) Get the value associated with key with code h.
private Object	getAfterMiss(ThreadLocal key, int i, ThreadLocal.ThreadLocalMap.Entry e) Version of get method for use when key is not found in its direct hash slot.
private static int	nextIndex(int i, int len) Increment i modulo len.
private static int	prevIndex(int i, int len) Decrement i modulo len.
private void	rehash() Re-pack and/or re-size the table.
private Object	replaceStaleEntry(ThreadLocal key, Object value, int staleSlot, boolean actAsGet) Replace a stale entry encountered during a get or set operation with an entry for the specified key.
private void	resize() Double the capacity of the table.
private void	set(ThreadLocal key, Object value) Set the value associated with key.
private void	setThreshold(int len) Set the resize threshold to maintain at worst a 2/3 load factor.

Methods inherited from class java.lang.Object

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

Field Detail

INITIAL_CAPACITY

private static final int INITIAL_CAPACITY

The initial capacity -- MUST be a power of two.

See Also:

Constant Field Values

table

private ThreadLocal.ThreadLocalMap.Entry[] table

The table, resized as necessary. table.length MUST always be a power of two.

size

private int size

The number of entries in the table.

threshold

private int threshold

The next size value at which to resize.

Constructor Detail

ThreadLocal.ThreadLocalMap

ThreadLocal.ThreadLocalMap(ThreadLocal firstKey,
                           Object firstValue)

Construct a new map initially containing (firstKey, firstValue). ThreadLocalMaps are constructed lazily, so we only create one when we have at least one entry to put in it.

ThreadLocal.ThreadLocalMap

private ThreadLocal.ThreadLocalMap(ThreadLocal.ThreadLocalMap parentMap)

Construct a new map including all Inheritable ThreadLocals from given parent map. Called only by createInheritedMap.

Parameters:

parentMap - the map associated with parent thread.

Method Detail

setThreshold

private void setThreshold(int len)

Set the resize threshold to maintain at worst a 2/3 load factor.

nextIndex

private static int nextIndex(int i,
                             int len)

Increment i modulo len.

prevIndex

private static int prevIndex(int i,
                             int len)

Decrement i modulo len.

get

private Object get(ThreadLocal key)

Get the value associated with key with code h. This method itself handles only the fast path: a direct hit of existing key. It otherwise relays to getAfterMiss. This is designed to maximize performance for direct hits, in part by making this method readily inlinable.

Parameters:

key - the thread local object

Returns:

the value associated with key

getAfterMiss

private Object getAfterMiss(ThreadLocal key,
                            int i,
                            ThreadLocal.ThreadLocalMap.Entry e)

Version of get method for use when key is not found in its direct hash slot.

Parameters:

key - the thread local object

i - the table index for key's hash code

e - the entry at table[i];

Returns:

the value associated with key

set

private void set(ThreadLocal key,
                 Object value)

Set the value associated with key.

Parameters:

key - the thread local object

value - the value to be set

replaceStaleEntry

private Object replaceStaleEntry(ThreadLocal key,
                                 Object value,
                                 int staleSlot,
                                 boolean actAsGet)

Replace a stale entry encountered during a get or set operation with an entry for the specified key. If actAsGet is true and an entry for the key already exists, the value in the entry is unchanged; if no entry exists for the key, the value in the new entry is obtained by calling key.initialValue. If actAsGet is false, the value passed in the value parameter is stored in the entry, whether or not an entry already exists for the specified key. As a side effect, this method expunges all stale entries in the "run" containing the stale entry. (A run is a sequence of entries between two null slots.)

Parameters:

key - the key

value - the value to be associated with key; meaningful only if actAsGet is false.

staleSlot - index of the first stale entry encountered while searching for key.

actAsGet - true if this method should act as a get; false it should act as a set.

Returns:

the value associated with key after the operation completes.

expungeStaleEntry

private void expungeStaleEntry(int staleSlot)

Expunge a stale entry by rehashing any possibly colliding entries lying between staleSlot and the next null slot. This also expunges any other stale entries encountered before the trailing null. See Knuth, Section 6.4

Parameters:

staleSlot - index of slot known to have null key

rehash

private void rehash()

Re-pack and/or re-size the table. First scan the entire table removing stale entries. If this doesn't sufficiently shrink the size of the table, double the table size.

resize

private void resize()

Double the capacity of the table.

expungeStaleEntries

private void expungeStaleEntries()

Expunge all stale entries in the table.