Hi,
I noticed that Classpath didn't have a implementation of
java.lang.ThreadLocal and java.lang.InheritableThreadLocal.
Since I was curious how one would implement these classes I did.
I tried to minimise the changes that would be necessary to java.lang.Thread
since that seems like a class that you don't want to change to much.
I finally came up with an implementation that uses WeakHashMap to store
the Thread references (so the values will disappear when the Thread object
is garbage collected) and with only one callback in InheritableThreadLocal
that should be called from the Thread constructor.
I have attached the files and a trivial patch to the Classpath reference
implementation of Thread.java that demonstrates the use of
InheritableThreadLocal.newChildThread().
Cheers,
Mark
/* java.lang.ThreadLocal
Copyright (C) 2000 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., 59 Temple Place, Suite 330, Boston, MA
02111-1307 USA.
As a special exception, if you link this library with other files to
produce an executable, this library does not by itself cause the
resulting executable to be covered by the GNU General Public License.
This exception does not however invalidate any other reasons why the
executable file might be covered by the GNU General Public License. */
package java.lang;
import java.util.Map;
import java.util.WeakHashMap;
/**
* ThreadLocal objects have a different state associated with every
* Thread that accesses them. Every access to the ThreadLocal object
* (through the <code>get()</code> and <code>set()</code> methods)
* only affects the state of the object as seen by the currently
* executing Thread.
* <p>
* The first time a ThreadLocal object is accessed on a particular
* Thread (and no state is associated with that Thread yet)
* the state for that Thread is set by executing the method
* <code>initialValue()</code>.
* <p>
* An example how you can use this:
* <pre>
* class Connection {
* private static ThreadLocal owner = new ThreadLocal() {
* public Object initialValue() {
* return("nobody");
* }
* };
* ...
* }
* </pre>
* Now all instances of connection can see who the owner of the currently
* executing Thread is by calling <code>owner.get()</code>. By default any
* Thread would be associated with 'nobody'. But the Connection object could
* offer a method that changes the owner associated with the Thread on
* which the method was called by calling <code>owner.put("somebody")</code>.
* (Such an owner changing method should then be guarded by security checks.)
* <p>
* When a Thread is garbage collected all references to values of
* the ThreadLocal objects associated with that Thread are removed.
*
* @since 1.2
* @author Mark Wielaard ([EMAIL PROTECTED])
*/
public class ThreadLocal {
/**
* Trivial container to wrap the stored values.
* Needed to see if the value is null or not yet set.
* If it is not yet set we must call intialValue() once.
* Package local so InheritableThreadLocal can see it.
*/
final static class Value {
final Object value;
Value(Object value) {
this.value = value;
}
Object getValue() {
return value;
}
}
/**
* Maps Threads to Values. Uses a WeakHashMap so if a Thread is garbage
* collected the reference to the Value will disappear. Only the
* <code>set(Thread, Value)</code> and <code>get(Thread)</code> methods
* access it. Since this can happen from multiple Threads simultaniously
* those methods are synchronized.
*/
private final Map valueMap = new WeakHashMap();
/**
* Creates a ThreadLocal object without associating any value to it
* yet.
*/
public ThreadLocal() {
}
/**
* Gets the value associated with the ThreadLocal object for the
* currently executing Thread. If there is no value is associated
* with this Thread yet then the valued returned by the
* <code>initialValue()</code> method is assosiated with this Thread
* and returned.
*/
public Object get() {
Thread currentThread = Thread.currentThread();
Value v = get(currentThread);
if (v == null) {
v = new Value(initialValue());
set(currentThread, v);
}
return v.getValue();
}
/**
* Gets the Value of this ThreadLocal for a particular Thread.
* It is synchronized so the <code>set(Thread, Value)</code> method cannot
* simultaniously modify the </code>valueMap</code> from another thread.
* Package local so InheritableThreadLocal can access it when a new child
* Thread inherits values from its parent Thread.
*/
synchronized final Value get(Thread thread) {
return (Value)valueMap.get(thread);
}
/**
* Sets the value associated with the ThreadLocal object for the
* currently executing Thread. This overrides any existing value
* associated with the current Thread and does not call the
* <code>initialValue()</code> method, even if this is the first
* time this Thread accesses this ThreadLocal.
*/
public void set(Object value) {
Thread currentThread = Thread.currentThread();
Value v = new Value(value);
set(currentThread, v);
}
/**
* Sets the Value for this ThreadLocal for a particular Thread.
* It is synchronized so the <code>get(Thread)</code> method cannot
* simultaniously read the </code>valueMap</code> from another thread.
* Package local so InheritableThreadLocal can access it when a new child
* Thread inherits values from its parent Thread.
*/
synchronized final void set(Thread thread, Value value) {
valueMap.put(thread, value);
}
/**
* Called when <code>get()</code> is called and no state is associated
* with the currently executing Thread yet.
* <p>
* The default implementation returns <code>null</code>.
*/
protected Object initialValue() {
return null;
}
}
/* java.lang.InheritableThreadLocal
Copyright (C) 2000 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., 59 Temple Place, Suite 330, Boston, MA
02111-1307 USA.
As a special exception, if you link this library with other files to
produce an executable, this library does not by itself cause the
resulting executable to be covered by the GNU General Public License.
This exception does not however invalidate any other reasons why the
executable file might be covered by the GNU General Public License. */
package java.lang;
import java.util.Iterator;
import java.util.HashSet;
import java.util.Map;
import java.util.Set;
import java.util.WeakHashMap;
/**
* ThreadLocal whose value is inherited by child Threads.
* The value of the InheritableThreadLocal associated with the (parent) Thread
* on the moment that it creates a new (child) Thread is set as the value that
* is associated with the new (child) Thread.
* <p>
* It is possible to make the value associated with the child Thread a function
* of the value that is associated with the parent Thread by overriding the
* <code>childValue()</code> method.
*
* @since 1.2
* @author Mark Wielaard ([EMAIL PROTECTED])
*/
public class InheritableThreadLocal extends ThreadLocal {
/**
* Maps Threads to a Set of InheritableThreadLocals
* (the heritage of that Thread).
* Uses a WeakHashMap so if the Thread is garbage collected the reference
* to that Set disappears.
* Both <code>AddToHeritage</code> access and modify it so they have to
* synchronize on the threadMap when they do.
*/
private static Map threadMap = new WeakHashMap();
/**
* Creates a new InheritableThreadLocal that has no values associated
* with it yet.
*/
public InheritableThreadLocal() {
super();
}
/**
* Determines the value associated with a newly created child Thread
* as a function of the value associated with the currently executing
* (parent) Thread.
* <p>
* The default implementation just returns the parentValue.
*/
protected Object childValue(Object parentValue) {
return parentValue;
}
/**
* Adds this <code>InheritableThreadLocal</code> to the heritage of the
* current Thread and returns the value of the <code>ThreadLocal</code>
* for the Thread. The value will be either the last value that the
* current Thread has set, or the childValue of the last value that the
* parent Thread set before the current Thread was created, or the
* initialValue of the <code>ThreadLocal</code>.
*
* @see ThreadLocal#get()
*/
public Object get() {
addToHeritage();
return super.get();
}
/**
* Adds this <code>InheritableThreadLocal</code> to the heritage of the
* current Thread and sets the value of the <code>ThreadLocal</code>
* for the Thread.
*
* @see ThreadLocal#set(Object)
*/
public void set(Object value) {
addToHeritage();
super.set(value);
}
/**
* Adds this <code>InheritableThreadLocal</code> to the heritage
* of the current Thread.
*/
private void addToHeritage() {
Thread currentThread = Thread.currentThread();
Set heritage;
synchronized(threadMap) {
heritage = (Set)threadMap.get(currentThread);
}
// Note that we don't have to synchronize on the heritage Set
// since only this Thread (or the parent Thread when creating
// the heritage) ever modifies it.
if (heritage == null) {
heritage = new HashSet();
synchronized(threadMap) {
threadMap.put(currentThread, heritage);
}
}
heritage.add(this);
}
/**
* Generates the childValues of all <code>InheritableThreadLocal</code>s
* that are in the heritage of the current Thread for the newly created
* childThread.
* Should be called from the contructor of java.lang.Thread.
*/
static void newChildThread(Thread childThread) {
// The currentThread is the parent of the new thread
Thread parentThread = Thread.currentThread();
// Inherit all the InheritableThreadLocals of the parent thread
Set heritage;
synchronized(threadMap) {
heritage = (Set)threadMap.get(parentThread);
}
// Note that we don't have to synchronize on the heritage Set
// since only this Thread (or the parent Thread when creating
// the heritage) ever modifies it.
if (heritage != null) {
synchronized(threadMap) {
threadMap.put(childThread, new HashSet(heritage));
}
// And constructs all the new child values
// (has to be done now that we are executing in the parentThread)
Iterator it = heritage.iterator();
while (it.hasNext()) {
InheritableThreadLocal local =
(InheritableThreadLocal) it.next();
// Note that the parentValue cannot be null
// If it was it would not be in the heritage
Object parentValue = local.get(parentThread).getValue();
Object childValue = local.childValue(parentValue);
ThreadLocal.Value v = new ThreadLocal.Value(childValue);
local.set(childThread, v);
}
}
}
}
--- vm/reference/java/lang/Thread.java 1999/11/18 02:22:31 1.9
+++ vm/reference/java/lang/Thread.java 2000/04/24 22:00:33
@@ -206,6 +206,7 @@
nativeInit();
this.group.addThread(this);
+ InheritableThreadLocal.newChildThread(this);
}
/** Get the currently executing Thread.
