Daniel's copyright assignment is finally through, so
I'm committing this patch which optimises the use of
ThreadLocals by replacing the use of the generic java.util.WeakHashMap
with a ThreadLocal-specific implementation.
ChangeLog:
2007-08-23 Daniel Frampton <[EMAIL PROTECTED]>
* AUTHORS: Added.
* java/lang/InheritableThreadLocal.java,
* java/lang/Thread.java,
* java/lang/ThreadLocal.java:
Modified to use java.lang.ThreadLocalMap.
* java/lang/ThreadLocalMap.java:
New cheaper ThreadLocal-specific WeakHashMap.
--
Andrew :)
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Index: java/lang/InheritableThreadLocal.java
===================================================================
RCS file: /sources/classpath/classpath/java/lang/InheritableThreadLocal.java,v
retrieving revision 1.13
diff -u -u -r1.13 InheritableThreadLocal.java
--- java/lang/InheritableThreadLocal.java 10 Dec 2006 20:25:44 -0000
1.13
+++ java/lang/InheritableThreadLocal.java 10 Sep 2008 01:51:42 -0000
@@ -37,10 +37,6 @@
package java.lang;
-import gnu.java.util.WeakIdentityHashMap;
-
-import java.util.Iterator;
-
/**
* A ThreadLocal whose value is inherited by child Threads. The value of the
* InheritableThreadLocal associated with the (parent) Thread is copied to
@@ -97,24 +93,6 @@
{
// The currentThread is the parent of the new thread.
Thread parentThread = Thread.currentThread();
- if (parentThread.locals != null)
- {
- Iterator keys = parentThread.locals.keySet().iterator();
- while (keys.hasNext())
- {
- Object key = keys.next();
- if (key instanceof InheritableThreadLocal)
- {
- InheritableThreadLocal local = (InheritableThreadLocal)key;
- Object parentValue = parentThread.locals.get(key);
- Object childValue = local.childValue(parentValue == sentinel
- ? null : parentValue);
- if (childThread.locals == null)
- childThread.locals = new WeakIdentityHashMap();
- childThread.locals.put(key, (childValue == null
- ? sentinel : childValue));
- }
- }
- }
+ childThread.locals.inherit(parentThread.locals);
}
}
Index: java/lang/Thread.java
===================================================================
RCS file: /sources/classpath/classpath/java/lang/Thread.java,v
retrieving revision 1.34
diff -u -u -r1.34 Thread.java
--- java/lang/Thread.java 10 Dec 2006 23:06:55 -0000 1.34
+++ java/lang/Thread.java 10 Sep 2008 01:51:43 -0000
@@ -159,7 +159,7 @@
/** Thread local storage. Package accessible for use by
* InheritableThreadLocal.
*/
- WeakIdentityHashMap locals;
+ final ThreadLocalMap locals;
/** The uncaught exception handler. */
UncaughtExceptionHandler exceptionHandler;
@@ -367,6 +367,7 @@
this.name = name.toString();
this.runnable = target;
this.stacksize = size;
+ this.locals = new ThreadLocalMap();
synchronized (Thread.class)
{
@@ -398,6 +399,7 @@
*/
Thread(VMThread vmThread, String name, int priority, boolean daemon)
{
+ this.locals = new ThreadLocalMap();
this.vmThread = vmThread;
this.runnable = null;
if (name == null)
@@ -1063,21 +1065,15 @@
{
group.removeThread(this);
vmThread = null;
- locals = null;
+ locals.clear();
}
/**
* Returns the map used by ThreadLocal to store the thread local values.
*/
- static Map getThreadLocals()
+ static ThreadLocalMap getThreadLocals()
{
- Thread thread = currentThread();
- Map locals = thread.locals;
- if (locals == null)
- {
- locals = thread.locals = new WeakIdentityHashMap();
- }
- return locals;
+ return currentThread().locals;
}
/**
Index: java/lang/ThreadLocal.java
===================================================================
RCS file: /sources/classpath/classpath/java/lang/ThreadLocal.java,v
retrieving revision 1.11
diff -u -u -r1.11 ThreadLocal.java
--- java/lang/ThreadLocal.java 10 Dec 2006 20:25:44 -0000 1.11
+++ java/lang/ThreadLocal.java 10 Sep 2008 01:51:44 -0000
@@ -37,9 +37,6 @@
package java.lang;
-import java.util.Map;
-
-
/**
* ThreadLocal objects have a different state associated with every
* Thread that accesses them. Every access to the ThreadLocal object
@@ -93,13 +90,31 @@
* user. Do not expose this to the public. Package visible for use by
* InheritableThreadLocal
*/
- static final Object sentinel = new Object();
+ static final Object notFound = new Object();
+
+ /**
+ * The base for the computation of the next hash for a thread local.
+ */
+ private static int nextHashBase = 1;
+
+ /**
+ * Allocate a new hash.
+ */
+ private synchronized int computeNextHash() {
+ return nextHashBase++ * 6709;
+ }
+
+ /**
+ * Hash code computed for ThreadLocalMap
+ */
+ final int fastHash;
/**
* Creates a ThreadLocal object without associating any value to it yet.
*/
public ThreadLocal()
{
+ fastHash = computeNextHash();
}
/**
@@ -125,16 +140,16 @@
*/
public T get()
{
- Map<ThreadLocal<T>,T> map = (Map<ThreadLocal<T>,T>)
Thread.getThreadLocals();
+ ThreadLocalMap map = Thread.getThreadLocals();
// Note that we don't have to synchronize, as only this thread will
// ever modify the map.
- T value = map.get(this);
- if (value == null)
+ T value = (T) map.get(this);
+ if (value == notFound)
{
value = initialValue();
- map.put(this, (T) (value == null ? sentinel : value));
+ map.set(this, value);
}
- return value == (T) sentinel ? null : value;
+ return value;
}
/**
@@ -147,10 +162,10 @@
*/
public void set(T value)
{
- Map map = Thread.getThreadLocals();
+ ThreadLocalMap map = Thread.getThreadLocals();
// Note that we don't have to synchronize, as only this thread will
// ever modify the map.
- map.put(this, value == null ? sentinel : value);
+ map.set(this, value);
}
/**
@@ -160,7 +175,7 @@
*/
public void remove()
{
- Map map = Thread.getThreadLocals();
+ ThreadLocalMap map = Thread.getThreadLocals();
map.remove(this);
}
}
Index: java/lang/ThreadLocalMap.java
===================================================================
RCS file: java/lang/ThreadLocalMap.java
diff -N java/lang/ThreadLocalMap.java
--- /dev/null 1 Jan 1970 00:00:00 -0000
+++ java/lang/ThreadLocalMap.java 10 Sep 2008 01:51:44 -0000
@@ -0,0 +1,325 @@
+/* ThreadLocal -- a variable with a unique value per thread
+ Copyright (C) 2000, 2002, 2003, 2004, 2005, 2006 Free Software Foundation,
Inc.
+
+This file is part of GNU Classpath.
+
+GNU Classpath is free software; you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation; either version 2, or (at your option)
+any later version.
+
+GNU Classpath is distributed in the hope that it will be useful, but
+WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with GNU Classpath; see the file COPYING. If not, write to the
+Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
+02110-1301 USA.
+
+Linking this library statically or dynamically with other modules is
+making a combined work based on this library. Thus, the terms and
+conditions of the GNU General Public License cover the whole
+combination.
+
+As a special exception, the copyright holders of this library give you
+permission to link this library with independent modules to produce an
+executable, regardless of the license terms of these independent
+modules, and to copy and distribute the resulting executable under
+terms of your choice, provided that you also meet, for each linked
+independent module, the terms and conditions of the license of that
+module. An independent module is a module which is not derived from
+or based on this library. If you modify this library, you may extend
+this exception to your version of the library, but you are not
+obligated to do so. If you do not wish to do so, delete this
+exception statement from your version. */
+
+package java.lang;
+
+import java.lang.ref.WeakReference;
+
+/**
+ * ThreadLocalMap is the basic storage for the map of ThreadLocal instance
+ * to a thread's current value.
+ *
+ * Some applications really work out ThreadLocals, leading to this
+ * optimized implementation.
+ */
+final class ThreadLocalMap
+{
+ /**
+ * The log (base 2) of the initial size of the map
+ */
+ private static final int LOG_INITIAL_SIZE = 3;
+
+ /**
+ * The maximum occupancy rate (after which we grow)
+ */
+ private static final float MAX_OCCUPANCY = 0.7f;
+
+ /**
+ * The target occupancy rate.
+ */
+ private static final float TARGET_OCCUPANCY = 0.5f;
+
+ /**
+ * The deleted entry sentinel value.
+ */
+ private static final Entry deletedEntry = new Entry(null);
+
+ /**
+ * Constructor
+ */
+ ThreadLocalMap()
+ {
+ /* Dummy value to ensure fast path can be optimized */
+ entries = new Entry[1];
+ hashMask = 0;
+ count = 0;
+ }
+
+ /**
+ * The map entries
+ */
+ private Entry[] entries;
+
+ /**
+ * Used for start index computation
+ */
+ private int hashMask;
+
+ /**
+ * The number of entries currently in the map
+ */
+ private int count;
+
+ /**
+ * Create or grow the table to the specified size. The size must be a
+ * power of two for the efficient mask/hash computation.
+ *
+ * @param newSize The new table size.
+ */
+ private void newEntryArray(int newSize)
+ {
+ int mask = newSize - 1;
+ Entry[] oldEntries = this.entries;
+ this.entries = new Entry[newSize];
+ this.hashMask = mask;
+
+ /* Copy old entries to new table */
+ count = 0;
+ if (oldEntries != null)
+ {
+ for(Entry e: oldEntries)
+ {
+ if (e != null)
+ {
+ ThreadLocal<?> key = e.get();
+ if (e != deletedEntry && key != null)
+ {
+ for(int i = key.fastHash & mask;; i = (i + 1) & mask)
+ {
+ if (entries[i] == null)
+ {
+ entries[i] = e;
+ count++;
+ break;
+ }
+ }
+ }
+ }
+ }
+ }
+ }
+
+ /**
+ * We have run out of space in our locals. We use this as the
+ * trigger to attempt to find unused slots as ThreadLocals have
+ * died. If we recover any slots this way then we do not grow.
+ */
+ private void overflow()
+ {
+ /* First 'actual' use */
+ if (entries.length == 1)
+ {
+ newEntryArray(1 << LOG_INITIAL_SIZE);
+ return;
+ }
+
+ /* Attempt to recover unused slots */
+ int deleted = 0;
+ for(int i=0; i < entries.length; i++)
+ {
+ Entry e = entries[i];
+ if (e != null)
+ {
+ if (e == deletedEntry)
+ {
+ deleted++;
+ }
+ else if (e.get() == null)
+ {
+ entries[i] = deletedEntry;
+ deleted++;
+ }
+ }
+ }
+
+ if ((count-deleted) <= (TARGET_OCCUPANCY * entries.length))
+ {
+ /* We currently rehash by simple reallocating into a same-sized table.
+ * An alternative would be to implement a clever hashing algorithm but
+ * as this happens infrequently this seems preferred */
+ newEntryArray(entries.length);
+ return;
+ }
+
+ /* Double the size */
+ newEntryArray(entries.length << 1);
+ }
+
+ /**
+ * This is the class that is used to refer to a thread local weakly.
+ *
+ * As we want to minimize indirections we extend WeakReference.
+ */
+ static final class Entry extends WeakReference<ThreadLocal<?>> {
+ /**
+ * The value stored in this slot
+ */
+ Object value;
+
+ /**
+ * Constructor
+ */
+ Entry(ThreadLocal<?> threadLocal) {
+ super(threadLocal);
+ }
+ }
+
+ /**
+ * Gets the value associated with the ThreadLocal object for the currently
+ * executing Thread. If this is the first time the current thread has called
+ * get(), and it has not already called set(), the sentinel value is
returned.
+ *
+ * @return the value of the variable in this thread, or sentinel if not
present.
+ */
+ public Object get(ThreadLocal<?> key)
+ {
+ int mask = this.hashMask;
+ for(int i = key.fastHash & mask;; i = (i + 1) & mask) {
+ Entry e = entries[i];
+ if (e != null) {
+ if (e.get() == key) {
+ return e.value;
+ }
+ } else {
+ return ThreadLocal.notFound;
+ }
+ }
+ }
+
+ /**
+ * Sets the value associated with the ThreadLocal object for the currently
+ * executing Thread. This overrides any existing value associated with the
+ * current Thread and prevents <code>initialValue()</code> from being
+ * called if this is the first access to this ThreadLocal in this Thread.
+ *
+ * @param value the value to set this thread's view of the variable to
+ */
+ public void set(ThreadLocal<?> key, Object value)
+ {
+ /* Overflow ? */
+ if ((count+1) >= (MAX_OCCUPANCY * entries.length))
+ {
+ overflow();
+ }
+
+ /* Set the entry */
+ int mask = this.hashMask;
+ for(int i = key.fastHash & mask;; i = (i + 1) & mask)
+ {
+ Entry e = entries[i];
+ if (e == null || e == deletedEntry)
+ {
+ /* Create entry */
+ if (e == null) count++;
+ entries[i] = e = new Entry(key);
+ e.value = value;
+ return;
+ }
+ else
+ {
+ ThreadLocal<?> entryKey = e.get();
+ if (entryKey == null)
+ {
+ entries[i] = deletedEntry;
+ }
+ else if (entryKey == key)
+ {
+ /* Update entry */
+ e.value = value;
+ return;
+ }
+ }
+ }
+ }
+
+ /**
+ * Removes the value associated with the ThreadLocal object for the
+ * currently executing Thread.
+ * @since 1.5
+ */
+ public void remove(ThreadLocal<?> key)
+ {
+ int mask = this.hashMask;
+ for(int i = key.fastHash & mask;; i = (i + 1) & mask)
+ {
+ Entry e = entries[i];
+ if (e != null)
+ {
+ ThreadLocal<?> entryKey = e.get();
+ if (entryKey != key)
+ {
+ if (entryKey == null) {
+ entries[i] = deletedEntry;
+ }
+ continue;
+ }
+ else
+ {
+ /* Remove from the table */
+ entries[i] = deletedEntry;
+ }
+ }
+ return;
+ }
+ }
+
+ /**
+ * Clear out the map. Done once during thread death.
+ */
+ void clear() {
+ entries = null;
+ }
+
+ /**
+ * Inherit all the InheritableThreadLocal instances from the given parent.
+ *
+ * @param parentMap The map to inherit from.
+ */
+ public void inherit(ThreadLocalMap parentMap) {
+ for(Entry e: parentMap.entries)
+ {
+ if (e != null && e != deletedEntry)
+ {
+ ThreadLocal<?> key = e.get();
+ if (key instanceof InheritableThreadLocal)
+ {
+ set(key, ((InheritableThreadLocal)key).childValue(e.value));
+ }
+ }
+ }
+ }
+}
