concurrenthashmap.java

来自「SRI international 发布的OAA框架软件」· Java 代码 · 共 1,427 行 · 第 1/4 页

                segments[i].lock();
            for (int i = 0; i < segments.length; ++i)
                sum += segments[i].count;
            for (int i = 0; i < segments.length; ++i)
                segments[i].unlock();
        }
        if (sum > Integer.MAX_VALUE)
            return Integer.MAX_VALUE;
        else
            return (int)sum;
    }


    /**
     * Returns the value to which the specified key is mapped in this table.
     *
     * @param   key   a key in the table.
     * @return  the value to which the key is mapped in this table;
     *          <tt>null</tt> if the key is not mapped to any value in
     *          this table.
     * @throws  NullPointerException  if the key is
     *               <tt>null</tt>.
     */
    public Object get(Object key) {
        int hash = hash(key); // throws NullPointerException if key null
        return segmentFor(hash).get(key, hash);
    }

    /**
     * Tests if the specified object is a key in this table.
     *
     * @param   key   possible key.
     * @return  <tt>true</tt> if and only if the specified object
     *          is a key in this table, as determined by the
     *          <tt>equals</tt> method; <tt>false</tt> otherwise.
     * @throws  NullPointerException  if the key is
     *               <tt>null</tt>.
     */
    public boolean containsKey(Object key) {
        int hash = hash(key); // throws NullPointerException if key null
        return segmentFor(hash).containsKey(key, hash);
    }

    /**
     * Returns <tt>true</tt> if this map maps one or more keys to the
     * specified value. Note: This method requires a full internal
     * traversal of the hash table, and so is much slower than
     * method <tt>containsKey</tt>.
     *
     * @param value value whose presence in this map is to be tested.
     * @return <tt>true</tt> if this map maps one or more keys to the
     * specified value.
     * @throws  NullPointerException  if the value is <tt>null</tt>.
     */
    public boolean containsValue(Object value) {
        if (value == null)
            throw new NullPointerException();

        // See explanation of modCount use above

        final Segment[] segments = this.segments;
        int[] mc = new int[segments.length];

        // Try a few times without locking
        for (int k = 0; k < RETRIES_BEFORE_LOCK; ++k) {
            int sum = 0;
            int mcsum = 0;
            for (int i = 0; i < segments.length; ++i) {
                int c = segments[i].count;
                mcsum += mc[i] = segments[i].modCount;
                if (segments[i].containsValue(value))
                    return true;
            }
            boolean cleanSweep = true;
            if (mcsum != 0) {
                for (int i = 0; i < segments.length; ++i) {
                    int c = segments[i].count;
                    if (mc[i] != segments[i].modCount) {
                        cleanSweep = false;
                        break;
                    }
                }
            }
            if (cleanSweep)
                return false;
        }
        // Resort to locking all segments
        for (int i = 0; i < segments.length; ++i)
            segments[i].lock();
        boolean found = false;
        try {
            for (int i = 0; i < segments.length; ++i) {
                if (segments[i].containsValue(value)) {
                    found = true;
                    break;
                }
            }
        } finally {
            for (int i = 0; i < segments.length; ++i)
                segments[i].unlock();
        }
        return found;
    }

    /**
     * Legacy method testing if some key maps into the specified value
     * in this table.  This method is identical in functionality to
     * {@link #containsValue}, and  exists solely to ensure
     * full compatibility with class {@link java.util.Hashtable},
     * which supported this method prior to introduction of the
     * Java Collections framework.

     * @param      value   a value to search for.
     * @return     <tt>true</tt> if and only if some key maps to the
     *             <tt>value</tt> argument in this table as
     *             determined by the <tt>equals</tt> method;
     *             <tt>false</tt> otherwise.
     * @throws  NullPointerException  if the value is <tt>null</tt>.
     */
    public boolean contains(Object value) {
        return containsValue(value);
    }

    /**
     * Maps the specified <tt>key</tt> to the specified
     * <tt>value</tt> in this table. Neither the key nor the
     * value can be <tt>null</tt>.
     *
     * <p> The value can be retrieved by calling the <tt>get</tt> method
     * with a key that is equal to the original key.
     *
     * @param      key     the table key.
     * @param      value   the value.
     * @return     the previous value of the specified key in this table,
     *             or <tt>null</tt> if it did not have one.
     * @throws  NullPointerException  if the key or value is
     *               <tt>null</tt>.
     */
    public Object put(Object key, Object value) {
        if (value == null)
            throw new NullPointerException();
        int hash = hash(key);
        return segmentFor(hash).put(key, hash, value, false);
    }

    /**
     * If the specified key is not already associated
     * with a value, associate it with the given value.
     * This is equivalent to
     * <pre>
     *   if (!map.containsKey(key))
     *      return map.put(key, value);
     *   else
     *      return map.get(key);
     * </pre>
     * Except that the action is performed atomically.
     * @param key key with which the specified value is to be associated.
     * @param value value to be associated with the specified key.
     * @return previous value associated with specified key, or <tt>null</tt>
     *         if there was no mapping for key.
     * @throws NullPointerException if the specified key or value is
     *            <tt>null</tt>.
     */
    public Object putIfAbsent(Object key, Object value) {
        if (value == null)
            throw new NullPointerException();
        int hash = hash(key);
        return segmentFor(hash).put(key, hash, value, true);
    }


    /**
     * Copies all of the mappings from the specified map to this one.
     *
     * These mappings replace any mappings that this map had for any of the
     * keys currently in the specified Map.
     *
     * @param t Mappings to be stored in this map.
     */
    public void putAll(Map t) {
        for (Iterator it = t.entrySet().iterator(); it.hasNext(); ) {
            Entry e = (Entry)it.next();
            put(e.getKey(), e.getValue());
        }
    }

    /**
     * Removes the key (and its corresponding value) from this
     * table. This method does nothing if the key is not in the table.
     *
     * @param   key   the key that needs to be removed.
     * @return  the value to which the key had been mapped in this table,
     *          or <tt>null</tt> if the key did not have a mapping.
     * @throws  NullPointerException  if the key is
     *               <tt>null</tt>.
     */
    public Object remove(Object key) {
        int hash = hash(key);
        return segmentFor(hash).remove(key, hash, null);
    }

    /**
     * Remove entry for key only if currently mapped to given value.
     * Acts as
     * <pre>
     *  if (map.get(key).equals(value)) {
     *     map.remove(key);
     *     return true;
     * } else return false;
     * </pre>
     * except that the action is performed atomically.
     * @param key key with which the specified value is associated.
     * @param value value associated with the specified key.
     * @return true if the value was removed
     * @throws NullPointerException if the specified key is
     *            <tt>null</tt>.
     */
    public boolean remove(Object key, Object value) {
        int hash = hash(key);
        return segmentFor(hash).remove(key, hash, value) != null;
    }


    /**
     * Replace entry for key only if currently mapped to given value.
     * Acts as
     * <pre>
     *  if (map.get(key).equals(oldValue)) {
     *     map.put(key, newValue);
     *     return true;
     * } else return false;
     * </pre>
     * except that the action is performed atomically.
     * @param key key with which the specified value is associated.
     * @param oldValue value expected to be associated with the specified key.
     * @param newValue value to be associated with the specified key.
     * @return true if the value was replaced
     * @throws NullPointerException if the specified key or values are
     * <tt>null</tt>.
     */
    public boolean replace(Object key, Object oldValue, Object newValue) {
        if (oldValue == null || newValue == null)
            throw new NullPointerException();
        int hash = hash(key);
        return segmentFor(hash).replace(key, hash, oldValue, newValue);
    }

    /**
     * Replace entry for key only if currently mapped to some value.
     * Acts as
     * <pre>
     *  if ((map.containsKey(key)) {
     *     return map.put(key, value);
     * } else return null;
     * </pre>
     * except that the action is performed atomically.
     * @param key key with which the specified value is associated.
     * @param value value to be associated with the specified key.
     * @return previous value associated with specified key, or <tt>null</tt>
     *         if there was no mapping for key.
     * @throws NullPointerException if the specified key or value is
     *            <tt>null</tt>.
     */
    public Object replace(Object key, Object value) {
        if (value == null)
            throw new NullPointerException();
        int hash = hash(key);
        return segmentFor(hash).replace(key, hash, value);
    }


    /**
     * Removes all mappings from this map.
     */
    public void clear() {
        for (int i = 0; i < segments.length; ++i)
            segments[i].clear();
    }


    /**
     * Returns a set view of the keys contained in this map.  The set is
     * backed by the map, so changes to the map are reflected in the set, and
     * vice-versa.  The set supports element removal, which removes the
     * corresponding mapping from this map, via the <tt>Iterator.remove</tt>,
     * <tt>Set.remove</tt>, <tt>removeAll</tt>, <tt>retainAll</tt>, and
     * <tt>clear</tt> operations.  It does not support the <tt>add</tt> or
     * <tt>addAll</tt> operations.
     * The view's returned <tt>iterator</tt> is a "weakly consistent" iterator that
     * will never throw {@link java.util.ConcurrentModificationException},
     * and guarantees to traverse elements as they existed upon
     * construction of the iterator, and may (but is not guaranteed to)
     * reflect any modifications subsequent to construction.
     *
     * @return a set view of the keys contained in this map.
     */
    public Set keySet() {
        Set ks = keySet;
        return (ks != null) ? ks : (keySet = new KeySet());
    }


    /**
     * Returns a collection view of the values contained in this map.  The
     * collection is backed by the map, so changes to the map are reflected in
     * the collection, and vice-versa.  The collection supports element
     * removal, which removes the corresponding mapping from this map, via the
     * <tt>Iterator.remove</tt>, <tt>Collection.remove</tt>,
     * <tt>removeAll</tt>, <tt>retainAll</tt>, and <tt>clear</tt> operations.
     * It does not support the <tt>add</tt> or <tt>addAll</tt> operations.
     * The view's returned <tt>iterator</tt> is a "weakly consistent" iterator that
     * will never throw {@link java.util.ConcurrentModificationException},
     * and guarantees to traverse elements as they existed upon
     * construction of the iterator, and may (but is not guaranteed to)
     * reflect any modifications subsequent to construction.
     *
     * @return a collection view of the values contained in this map.
     */
    public Collection values() {
        Collection vs = values;
        return (vs != null) ? vs : (values = new Values());
    }


    /**
     * Returns a collection view of the mappings contained in this map.  Each
     * element in the returned collection is a <tt>Map.Entry</tt>.  The
     * collection is backed by the map, so changes to the map are reflected in
     * the collection, and vice-versa.  The collection supports element
     * removal, which removes the corresponding mapping from the map, via the
     * <tt>Iterator.remove</tt>, <tt>Collection.remove</tt>,
     * <tt>removeAll</tt>, <tt>retainAll</tt>, and <tt>clear</tt> operations.
     * It does not support the <tt>add</tt> or <tt>addAll</tt> operations.
     * The view's returned <tt>iterator</tt> is a "weakly consistent" iterator that
     * will never throw {@link java.util.ConcurrentModificationException},
     * and guarantees to traverse elements as they existed upon
     * construction of the iterator, and may (but is not guaranteed to)
     * reflect any modifications subsequent to construction.
     *
     * @return a collection view of the mappings contained in this map.
     */
    public Set entrySet() {
        Set es = entrySet;
        return (es != null) ? es : (entrySet = new EntrySet());
    }


    /**
     * Returns an enumeration of the keys in this table.
     *
     * @return  an enumeration of the keys in this table.
     * @see     #keySet
     */
    public Enumeration keys() {
        return new KeyIterator();
    }