--- old/src/share/classes/java/lang/ThreadLocal.java 2012-12-05 11:23:53.807709963 -0800
+++ new/src/share/classes/java/lang/ThreadLocal.java 2012-12-05 11:23:53.635709971 -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;
@@ -61,11 +63,20 @@
* }
*
* 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).
*
+ * The initial value of the variable is set by (1) calling the
+ * {@code initialValue method}, (2) obtaining it from a {@code Supplier}
+ * which has been provided via the
+ * constructor, or (3) by calling the {@code set} method.
+ *
+ * If (1) is used and an initial value other than the default of null is required,
+ * the {@code initialValue} method is typically overridden with an
+ * anonymous-inner class.
+ *
* @author Josh Bloch and Doug Lea
* @since 1.2
*/
@@ -97,6 +108,11 @@
private static final int HASH_INCREMENT = 0x61c88647;
/**
+ * Supplied by the invoker of the constructor to set the initial value
+ */
+ private final Supplier supplier;
+
+ /**
* Returns the next hash code.
*/
private static int nextHashCode() {
@@ -105,19 +121,17 @@
/**
* Returns the current thread's "initial value" for this
- * thread-local variable. This method will be invoked the first
+ * thread-local variable unless a {@code Supplier} has been passed
+ * to the constructor, in which case the Supplier is consulted in
+ * preference to this method. 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
- * programmer desires thread-local variables to have an initial
- * value other than null, ThreadLocal must be
- * subclassed, and this method overridden. Typically, an
- * anonymous inner class will be used.
+ *
This implementation simply returns {@code null}
*
* @return the initial value for this thread-local
*/
@@ -126,9 +140,21 @@
}
/**
- * Creates a thread local variable.
+ * Creates a thread local variable. The initial value of the variable is
+ * provided by calling the {@code intialValue} method.
*/
public ThreadLocal() {
+ supplier = null;
+ }
+
+ /**
+ * Creates a thread local variable. The initial value of the variable is
+ * determined by invoking the {@code get} method on the supplier.
+ *
+ * @param supplier the supplier to be used to determine the initial value
+ */
+ public ThreadLocal(Supplier supplier) {
+ this.supplier = Objects.requireNonNull(supplier);
}
/**
@@ -160,7 +186,7 @@
* @return the initial value
*/
private T setInitialValue() {
- T value = initialValue();
+ T value = (supplier != null ? supplier.get() : initialValue());
Thread t = Thread.currentThread();
ThreadLocalMap map = getMap(t);
if (map != null)
@@ -195,7 +221,7 @@
* 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
*/
@@ -228,7 +254,7 @@
}
/**
- * Factory method to create map of inherited thread locals.
+ * Factory method to create map of inherited thread locals.
* Designed to be called only from Thread constructor.
*
* @param parentMap the map associated with parent thread
@@ -599,9 +625,9 @@
* @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