mirror of git://gcc.gnu.org/git/gcc.git
326 lines
8.8 KiB
Java
326 lines
8.8 KiB
Java
/* ThreadLocal -- a variable with a unique value per thread
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Copyright (C) 2000, 2002, 2003, 2004, 2005, 2006 Free Software Foundation, Inc.
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This file is part of GNU Classpath.
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GNU Classpath is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 2, or (at your option)
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any later version.
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GNU Classpath is distributed in the hope that it will be useful, but
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WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with GNU Classpath; see the file COPYING. If not, write to the
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Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
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02110-1301 USA.
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Linking this library statically or dynamically with other modules is
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making a combined work based on this library. Thus, the terms and
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conditions of the GNU General Public License cover the whole
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combination.
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As a special exception, the copyright holders of this library give you
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permission to link this library with independent modules to produce an
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executable, regardless of the license terms of these independent
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modules, and to copy and distribute the resulting executable under
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terms of your choice, provided that you also meet, for each linked
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independent module, the terms and conditions of the license of that
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module. An independent module is a module which is not derived from
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or based on this library. If you modify this library, you may extend
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this exception to your version of the library, but you are not
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obligated to do so. If you do not wish to do so, delete this
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exception statement from your version. */
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package java.lang;
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import java.lang.ref.WeakReference;
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/**
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* ThreadLocalMap is the basic storage for the map of ThreadLocal instance
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* to a thread's current value.
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*
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* Some applications really work out ThreadLocals, leading to this
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* optimized implementation.
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*/
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final class ThreadLocalMap
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{
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/**
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* The log (base 2) of the initial size of the map
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*/
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private static final int LOG_INITIAL_SIZE = 3;
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/**
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* The maximum occupancy rate (after which we grow)
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*/
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private static final float MAX_OCCUPANCY = 0.7f;
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/**
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* The target occupancy rate.
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*/
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private static final float TARGET_OCCUPANCY = 0.5f;
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/**
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* The deleted entry sentinel value.
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*/
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private static final Entry deletedEntry = new Entry(null);
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/**
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* Constructor
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*/
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ThreadLocalMap()
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{
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/* Dummy value to ensure fast path can be optimized */
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entries = new Entry[1];
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hashMask = 0;
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count = 0;
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}
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/**
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* The map entries
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*/
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private Entry[] entries;
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/**
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* Used for start index computation
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*/
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private int hashMask;
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/**
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* The number of entries currently in the map
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*/
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private int count;
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/**
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* Create or grow the table to the specified size. The size must be a
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* power of two for the efficient mask/hash computation.
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*
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* @param newSize The new table size.
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*/
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private void newEntryArray(int newSize)
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{
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int mask = newSize - 1;
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Entry[] oldEntries = this.entries;
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this.entries = new Entry[newSize];
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this.hashMask = mask;
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/* Copy old entries to new table */
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count = 0;
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if (oldEntries != null)
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{
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for(Entry e: oldEntries)
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{
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if (e != null)
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{
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ThreadLocal<?> key = e.get();
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if (e != deletedEntry && key != null)
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{
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for(int i = key.fastHash & mask;; i = (i + 1) & mask)
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{
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if (entries[i] == null)
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{
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entries[i] = e;
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count++;
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break;
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}
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}
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}
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}
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}
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}
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}
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/**
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* We have run out of space in our locals. We use this as the
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* trigger to attempt to find unused slots as ThreadLocals have
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* died. If we recover any slots this way then we do not grow.
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*/
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private void overflow()
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{
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/* First 'actual' use */
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if (entries.length == 1)
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{
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newEntryArray(1 << LOG_INITIAL_SIZE);
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return;
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}
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/* Attempt to recover unused slots */
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int deleted = 0;
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for(int i=0; i < entries.length; i++)
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{
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Entry e = entries[i];
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if (e != null)
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{
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if (e == deletedEntry)
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{
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deleted++;
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}
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else if (e.get() == null)
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{
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entries[i] = deletedEntry;
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deleted++;
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}
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}
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}
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if ((count-deleted) <= (TARGET_OCCUPANCY * entries.length))
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{
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/* We currently rehash by simple reallocating into a same-sized table.
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* An alternative would be to implement a clever hashing algorithm but
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* as this happens infrequently this seems preferred */
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newEntryArray(entries.length);
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return;
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}
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/* Double the size */
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newEntryArray(entries.length << 1);
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}
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/**
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* This is the class that is used to refer to a thread local weakly.
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*
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* As we want to minimize indirections we extend WeakReference.
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*/
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static final class Entry extends WeakReference<ThreadLocal<?>> {
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/**
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* The value stored in this slot
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*/
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Object value;
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/**
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* Constructor
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*/
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Entry(ThreadLocal<?> threadLocal) {
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super(threadLocal);
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}
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}
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/**
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* Gets the value associated with the ThreadLocal object for the currently
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* executing Thread. If this is the first time the current thread has called
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* get(), and it has not already called set(), the sentinel value is returned.
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*
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* @return the value of the variable in this thread, or sentinel if not present.
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*/
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public Object get(ThreadLocal<?> key)
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{
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int mask = this.hashMask;
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for(int i = key.fastHash & mask;; i = (i + 1) & mask) {
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Entry e = entries[i];
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if (e != null) {
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if (e.get() == key) {
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return e.value;
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}
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} else {
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return ThreadLocal.sentinel;
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}
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}
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}
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/**
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* Sets the value associated with the ThreadLocal object for the currently
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* executing Thread. This overrides any existing value associated with the
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* current Thread and prevents <code>initialValue()</code> from being
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* called if this is the first access to this ThreadLocal in this Thread.
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*
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* @param value the value to set this thread's view of the variable to
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*/
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public void set(ThreadLocal<?> key, Object value)
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{
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/* Overflow ? */
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if ((count+1) >= (MAX_OCCUPANCY * entries.length))
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{
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overflow();
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}
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/* Set the entry */
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int mask = this.hashMask;
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for(int i = key.fastHash & mask;; i = (i + 1) & mask)
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{
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Entry e = entries[i];
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if (e == null || e == deletedEntry)
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{
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/* Create entry */
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if (e == null) count++;
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entries[i] = e = new Entry(key);
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e.value = value;
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return;
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}
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else
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{
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ThreadLocal<?> entryKey = e.get();
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if (entryKey == null)
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{
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entries[i] = deletedEntry;
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}
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else if (entryKey == key)
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{
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/* Update entry */
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e.value = value;
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return;
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}
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}
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}
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}
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/**
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* Removes the value associated with the ThreadLocal object for the
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* currently executing Thread.
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* @since 1.5
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*/
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public void remove(ThreadLocal<?> key)
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{
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int mask = this.hashMask;
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for(int i = key.fastHash & mask;; i = (i + 1) & mask)
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{
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Entry e = entries[i];
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if (e != null)
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{
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ThreadLocal<?> entryKey = e.get();
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if (entryKey != key)
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{
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if (entryKey == null) {
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entries[i] = deletedEntry;
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}
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continue;
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}
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else
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{
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/* Remove from the table */
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entries[i] = deletedEntry;
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}
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}
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return;
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}
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}
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/**
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* Clear out the map. Done once during thread death.
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*/
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void clear() {
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entries = null;
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}
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/**
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* Inherit all the InheritableThreadLocal instances from the given parent.
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*
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* @param parentMap The map to inherit from.
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*/
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public void inherit(ThreadLocalMap parentMap) {
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for(Entry e: parentMap.entries)
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{
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if (e != null && e != deletedEntry)
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{
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ThreadLocal<?> key = e.get();
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if (key instanceof InheritableThreadLocal)
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{
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set(key, ((InheritableThreadLocal)key).childValue(e.value));
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}
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}
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}
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}
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}
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