| /* |
| * Copyright (c) 2010, 2013, 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. |
| */ |
| |
| package jdk.nashorn.internal.runtime; |
| |
| import static jdk.nashorn.internal.runtime.JSType.isString; |
| |
| import java.util.ArrayDeque; |
| import java.util.Deque; |
| |
| /** |
| * This class represents a string composed of two parts which may themselves be |
| * instances of <tt>ConsString</tt> or {@link String}. Copying of characters to |
| * a proper string is delayed until it becomes necessary. |
| */ |
| public final class ConsString implements CharSequence { |
| |
| private CharSequence left, right; |
| private final int length; |
| private volatile int state = STATE_NEW; |
| |
| private final static int STATE_NEW = 0; |
| private final static int STATE_THRESHOLD = 2; |
| private final static int STATE_FLATTENED = -1; |
| |
| /** |
| * Constructor |
| * |
| * Takes two {@link CharSequence} instances that, concatenated, forms this {@code ConsString} |
| * |
| * @param left left char sequence |
| * @param right right char sequence |
| */ |
| public ConsString(final CharSequence left, final CharSequence right) { |
| assert isString(left); |
| assert isString(right); |
| this.left = left; |
| this.right = right; |
| length = left.length() + right.length(); |
| if (length < 0) { |
| throw new IllegalArgumentException("too big concatenated String"); |
| } |
| } |
| |
| @Override |
| public String toString() { |
| return (String) flattened(true); |
| } |
| |
| @Override |
| public int length() { |
| return length; |
| } |
| |
| @Override |
| public char charAt(final int index) { |
| return flattened(true).charAt(index); |
| } |
| |
| @Override |
| public CharSequence subSequence(final int start, final int end) { |
| return flattened(true).subSequence(start, end); |
| } |
| |
| /** |
| * Returns the components of this ConsString as a {@code CharSequence} array with two elements. |
| * The elements will be either {@code Strings} or other {@code ConsStrings}. |
| * @return CharSequence array of length 2 |
| */ |
| public synchronized CharSequence[] getComponents() { |
| return new CharSequence[] { left, right }; |
| } |
| |
| private CharSequence flattened(final boolean flattenNested) { |
| if (state != STATE_FLATTENED) { |
| flatten(flattenNested); |
| } |
| return left; |
| } |
| |
| private synchronized void flatten(final boolean flattenNested) { |
| // We use iterative traversal as recursion may exceed the stack size limit. |
| final char[] chars = new char[length]; |
| int pos = length; |
| // Strings are most often composed by appending to the end, which causes ConsStrings |
| // to be very unbalanced, with mostly single string elements on the right and a long |
| // linear list on the left. Traversing from right to left helps to keep the stack small |
| // in this scenario. |
| final Deque<CharSequence> stack = new ArrayDeque<>(); |
| stack.addFirst(left); |
| CharSequence cs = right; |
| |
| do { |
| if (cs instanceof ConsString) { |
| final ConsString cons = (ConsString) cs; |
| // Count the times a cons-string is traversed as part of other cons-strings being flattened. |
| // If it crosses a threshold we flatten the nested cons-string internally. |
| if (cons.state == STATE_FLATTENED || (flattenNested && ++cons.state >= STATE_THRESHOLD)) { |
| cs = cons.flattened(false); |
| } else { |
| stack.addFirst(cons.left); |
| cs = cons.right; |
| } |
| } else { |
| final String str = (String) cs; |
| pos -= str.length(); |
| str.getChars(0, str.length(), chars, pos); |
| cs = stack.isEmpty() ? null : stack.pollFirst(); |
| } |
| } while (cs != null); |
| |
| left = new String(chars); |
| right = ""; |
| state = STATE_FLATTENED; |
| } |
| |
| } |