atomicreference.java

来自「SRI international 发布的OAA框架软件」· Java 代码 · 共 105 行

/*
 * Written by Doug Lea with assistance from members of JCP JSR-166
 * Expert Group and released to the public domain, as explained at
 * http://creativecommons.org/licenses/publicdomain
 */

package edu.emory.mathcs.backport.java.util.concurrent.atomic;

/**
 * An object reference that may be updated atomically. See the {@link
 * edu.emory.mathcs.backport.java.util.concurrent.atomic} package specification for description
 * of the properties of atomic variables.
 * @since 1.5
 * @author Doug Lea
 */
public class AtomicReference  implements java.io.Serializable {
    private static final long serialVersionUID = -1848883965231344442L;

    private Object value;

    /**
     * Create a new AtomicReference with the given initial value.
     *
     * @param initialValue the initial value
     */
    public AtomicReference(Object initialValue) {
        value = initialValue;
    }

    /**
     * Create a new AtomicReference with null initial value.
     */
    public AtomicReference() {
    }

    /**
     * Get the current value.
     *
     * @return the current value
     */
    public final synchronized Object get() {
        return value;
    }

    /**
     * Set to the given value.
     *
     * @param newValue the new value
     */
    public final synchronized void set(Object newValue) {
        value = newValue;
    }

    /**
     * Atomically set the value to the given updated value
     * if the current value <tt>==</tt> the expected value.
     * @param expect the expected value
     * @param update the new value
     * @return true if successful. False return indicates that
     * the actual value was not equal to the expected value.
     */
    public final synchronized boolean compareAndSet(Object expect, Object update) {
        boolean success = (expect == value);
        if (success)
            value = update;
        return success;
    }

    /**
     * Atomically set the value to the given updated value
     * if the current value <tt>==</tt> the expected value.
     * May fail spuriously.
     * @param expect the expected value
     * @param update the new value
     * @return true if successful.
     */
    public final synchronized boolean weakCompareAndSet(Object expect, Object update) {
        boolean success = (expect == value);
        if (success)
            value = update;
        return success;
    }

    /**
     * Set to the given value and return the old value.
     *
     * @param newValue the new value
     * @return the previous value
     */
    public final synchronized Object getAndSet(Object newValue) {
        Object old = value;
        value = newValue;
        return old;
    }

    /**
     * Returns the String representation of the current value.
     * @return the String representation of the current value.
     */
    public String toString() {
        return String.valueOf(get());
    }

}