Optimise storage of ThreadLocals.

2007-08-23  Daniel Frampton  <zyridium@zyridium.net>

	* 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.

6 files changed, 371 insertions, 45 deletions

diff --git a/AUTHORS b/AUTHORS
index 19a2658b7..ebd744253 100644
--- a/AUTHORS
+++ b/AUTHORS
@@ -19,6 +19,7 @@ David Daney (ddaney@avtrex.com)
 Nic Ferrier (nferrier@tapsellferrier.co.uk)
 Paul Fisher (rao@gnu.org)
 Thomas Fitzsimmons (fitzsim@redhat.com)
+Daniel Frampton (zyridium@zyridium.net)
 Jeroen Frijters (jeroen@frijters.net)
 David Gilbert (david.gilbert@object-refinery.com)
 Anthony Green (green@redhat.com)
diff --git a/ChangeLog b/ChangeLog
index e6d4cbf7f..fb467497f 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,13 @@
+2007-08-23  Daniel Frampton  <zyridium@zyridium.net>
+
+	* 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.
+
 2008-02-07  Ian Rogers  <ian.rogers@manchester.ac.uk>
 
 	* java/util/zip/ZipEntry.java:
diff --git a/java/lang/InheritableThreadLocal.java b/java/lang/InheritableThreadLocal.java
index 2079a4c20..07d52b5d0 100644
--- a/java/lang/InheritableThreadLocal.java
+++ b/java/lang/InheritableThreadLocal.java
@@ -37,10 +37,6 @@ exception statement from your version. */
 
 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 @@ public class InheritableThreadLocal<T> extends ThreadLocal<T>
   {
     // 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);
   }
 }
diff --git a/java/lang/Thread.java b/java/lang/Thread.java
index 01b380b67..82e726187 100644
--- a/java/lang/Thread.java
+++ b/java/lang/Thread.java
@@ -159,7 +159,7 @@ public class Thread implements Runnable
   /** Thread local storage. Package accessible for use by
     * InheritableThreadLocal.
     */
-  WeakIdentityHashMap locals;
+  final ThreadLocalMap locals;
 
   /** The uncaught exception handler.  */
   UncaughtExceptionHandler exceptionHandler;
@@ -367,6 +367,7 @@ public class Thread implements Runnable
     this.name = name.toString();
     this.runnable = target;
     this.stacksize = size;
+    this.locals = new ThreadLocalMap();
     
     synchronized (Thread.class)
       {
@@ -398,6 +399,7 @@ public class Thread implements Runnable
    */
   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 @@ public class Thread implements Runnable
   {
     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;
   }
 
   /** 
diff --git a/java/lang/ThreadLocal.java b/java/lang/ThreadLocal.java
index 6c4ba176a..14778c65c 100644
--- a/java/lang/ThreadLocal.java
+++ b/java/lang/ThreadLocal.java
@@ -37,9 +37,6 @@ exception statement from your version. */
 
 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 @@ public class ThreadLocal<T>
    * 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 class ThreadLocal<T>
    */
   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 class ThreadLocal<T>
    */
   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 class ThreadLocal<T>
    */
   public void remove()
   {
-    Map map = Thread.getThreadLocals();
+    ThreadLocalMap map = Thread.getThreadLocals();
     map.remove(this);
   }
 }
diff --git a/java/lang/ThreadLocalMap.java b/java/lang/ThreadLocalMap.java
new file mode 100644
index 000000000..c163cfeb1
--- /dev/null
+++ b/java/lang/ThreadLocalMap.java
@@ -0,0 +1,326 @@
+/* ThreadLocalMap -- a weak hash map optimised for ThreadLocal storage
+   Copyright (C) 2000, 2002, 2003, 2004, 2005, 2006, 2007
+   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));
+              }
+          }
+      }
+  }
+}