--- old/src/share/classes/java/lang/ThreadLocal.java 2012-12-06 11:26:04.876545132 -0800 +++ new/src/share/classes/java/lang/ThreadLocal.java 2012-12-06 11:26:04.708545125 -0800 @@ -25,19 +25,21 @@ package java.lang; import java.lang.ref.*; +import java.util.Objects; import java.util.concurrent.atomic.AtomicInteger; +import java.util.function.Supplier; /** * This class provides thread-local variables. These variables differ from * their normal counterparts in that each thread that accesses one (via its - * get or set method) has its own, independently initialized - * copy of the variable. ThreadLocal instances are typically private + * {@code get} or {@code set} method) has its own, independently initialized + * copy of the variable. {@code ThreadLocal} instances are typically private * static fields in classes that wish to associate state with a thread (e.g., * a user ID or Transaction ID). * *

For example, the class below generates unique identifiers local to each * thread. - * A thread's id is assigned the first time it invokes ThreadId.get() + * A thread's id is assigned the first time it invokes {@code ThreadId.get()} * and remains unchanged on subsequent calls. *

  * import java.util.concurrent.atomic.AtomicInteger;
@@ -61,7 +63,7 @@
  * }
  * 
*

Each thread holds an implicit reference to its copy of a thread-local - * variable as long as the thread is alive and the ThreadLocal + * variable as long as the thread is alive and the {@code ThreadLocal} * instance is accessible; after a thread goes away, all of its copies of * thread-local instances are subject to garbage collection (unless other * references to these copies exist). @@ -108,14 +110,14 @@ * thread-local variable. This method will be invoked the first * time a thread accesses the variable with the {@link #get} * method, unless the thread previously invoked the {@link #set} - * method, in which case the initialValue method will not + * method, in which case the {@code initialValue} method will not * be invoked for the thread. Normally, this method is invoked at * most once per thread, but it may be invoked again in case of * subsequent invocations of {@link #remove} followed by {@link #get}. * - *

This implementation simply returns null; if the + *

This implementation simply returns {@code null}; if the * programmer desires thread-local variables to have an initial - * value other than null, ThreadLocal must be + * value other than {@code null}, {@code ThreadLocal} must be * subclassed, and this method overridden. Typically, an * anonymous inner class will be used. * @@ -126,7 +128,20 @@ } /** + * Creates a thread local variable. The initial value of the variable is + * determined by invoking the {@code get} method on the {@code Supplier}. + * + * @param supplier the supplier to be used to determine the initial value + * @return a new thread local variable + * @since 1.8 + */ + public static ThreadLocal withInitial(Supplier supplier) { + return new SuppliedThreadLocal<>(supplier); + } + + /** * Creates a thread local variable. + * @see #withInitial(java.util.function.Supplier) */ public ThreadLocal() { } @@ -195,7 +210,7 @@ * reinitialized by invoking its {@link #initialValue} method, * unless its value is {@linkplain #set set} by the current thread * in the interim. This may result in multiple invocations of the - * initialValue method in the current thread. + * {@code initialValue} method in the current thread. * * @since 1.5 */ @@ -251,6 +266,24 @@ } /** + * An extension of ThreadLocal that obtains its initial value from + * the specified {@code Supplier}. + */ + static final class SuppliedThreadLocal extends ThreadLocal { + + private final Supplier supplier; + + SuppliedThreadLocal(Supplier supplier) { + this.supplier = Objects.requireNonNull(supplier); + } + + @Override + protected T initialValue() { + return supplier.get(); + } + } + + /** * 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 @@ -599,9 +632,9 @@ * @param i a position known NOT to hold a stale entry. The * scan starts at the element after i. * - * @param n scan control: log2(n) cells are scanned, + * @param n scan control: {@code log2(n)} cells are scanned, * unless a stale entry is found, in which case - * log2(table.length)-1 additional cells are scanned. + * {@code log2(table.length)-1} additional cells are scanned. * When called from insertions, this parameter is the number * of elements, but when from replaceStaleEntry, it is the * table length. (Note: all this could be changed to be either --- /dev/null 2012-12-06 07:38:24.048736337 -0800 +++ new/test/java/lang/ThreadLocal/ThreadLocalSupplierTest.java 2012-12-06 11:26:05.488545155 -0800 @@ -0,0 +1,127 @@ +/* + * Copyright (c) 2012, Oracle and/or its affiliates. All rights reserved. + * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. + * + * This code is free software; you can redistribute it and/or modify it + * under the terms of the GNU General Public License version 2 only, as + * published by the Free Software Foundation. Oracle designates this + * particular file as subject to the "Classpath" exception as provided + * by Oracle in the LICENSE file that accompanied this code. + * + * This code 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 + * version 2 for more details (a copy is included in the LICENSE file that + * accompanied this code). + * + * You should have received a copy of the GNU General Public License version + * 2 along with this work; if not, write to the Free Software Foundation, + * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. + * + * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA + * or visit www.oracle.com if you need additional information or have any + * questions. + */ + +import java.util.concurrent.atomic.AtomicInteger; +import java.util.function.Supplier; +import org.testng.annotations.Test; +import static org.testng.Assert.*; + +/** + * @test + * @run testng ThreadLocalSupplierTest + * @summary tests ThreadLocal.withInitial(). + * Adapted from java.lang.Basic functional test of ThreadLocal + * + * @author Jim Gish + */ +@Test +public class ThreadLocalSupplierTest { + + static final class IntegerSupplier implements Supplier { + + private final AtomicInteger supply = new AtomicInteger(0); + + @Override + public Integer get() { + return supply.getAndIncrement(); + } + + public int numCalls() { + return supply.intValue(); + } + } + + static IntegerSupplier theSupply = new IntegerSupplier(); + + static final class MyThreadLocal extends ThreadLocal { + + private final ThreadLocal delegate; + + public volatile boolean everCalled; + + public MyThreadLocal(Supplier supplier) { + delegate = ThreadLocal.withInitial(supplier); + } + + @Override + public Integer get() { + return delegate.get(); + } + + @Override + protected synchronized Integer initialValue() { + // this should never be called since we are using the factory instead + everCalled = true; + return null; + } + } + + /** + * Our one and only ThreadLocal from which we get thread ids using a + * supplier which simply increments a counter on each call of get(). + */ + static MyThreadLocal threadLocal = new MyThreadLocal(theSupply); + + public void testMultiThread() throws Exception { + final int threadCount = 500; + final Thread th[] = new Thread[threadCount]; + final boolean visited[] = new boolean[threadCount]; + + // Create and start the threads + for (int i = 0; i < threadCount; i++) { + th[i] = new Thread() { + @Override + public void run() { + final int threadId = threadLocal.get(); + assertFalse(visited[threadId], "visited[" + threadId + "]=" + visited[threadId]); + visited[threadId] = true; + // check the get() again + final int secondCheckThreadId = threadLocal.get(); + assertEquals(secondCheckThreadId, threadId); + } + }; + th[i].start(); + } + + // Wait for the threads to finish + for (int i = 0; i < threadCount; i++) { + th[i].join(); + } + + assertEquals(theSupply.numCalls(), threadCount); + // make sure the provided initialValue() has not been called + assertFalse(threadLocal.everCalled); + // Check results + for (int i = 0; i < threadCount; i++) { + assertTrue(visited[i], "visited[" + i + "]=" + visited[i]); + } + } + + public void testSimple() { + final String expected = "OneWithEverything"; + final ThreadLocal threadLocal = ThreadLocal.withInitial(() -> expected); + assertEquals(expected, threadLocal.get()); + } +}