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/*
*
* ***** BEGIN LICENSE BLOCK *****
* Version: MPL 1.1/GPL 2.0
*
* The contents of this file are subject to the Mozilla Public License Version
* 1.1 (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
* http://www.mozilla.org/MPL/
*
* Software distributed under the License is distributed on an "AS IS" basis,
* WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
* for the specific language governing rights and limitations under the
* License.
*
* The Original Code is Rhino code, released
* May 6, 1999.
*
* The Initial Developer of the Original Code is
* Netscape Communications Corporation.
* Portions created by the Initial Developer are Copyright (C) 1997-1999
* the Initial Developer. All Rights Reserved.
*
* Contributor(s):
* Google Inc.
*
* Alternatively, the contents of this file may be used under the terms of
* the GNU General Public License Version 2 or later (the "GPL"), in which
* case the provisions of the GPL are applicable instead of those above. If
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* MPL, indicate your decision by deleting the provisions above and replacing
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* not delete the provisions above, a recipient may use your version of this
* file under either the MPL or the GPL.
*
* ***** END LICENSE BLOCK ***** */
package com.google.javascript.rhino;
import static com.google.javascript.jscomp.base.JSCompObjects.identical;
import com.google.common.collect.Interner;
import com.google.common.collect.Interners;
/**
* An interning pool for strings used by the Rhino package.
*
* As of 2021-03-16, this custom pool is measurably more performant than `String::intern`. Some
* reasons for this are presented at https://shipilev.net/jvm/anatomy-quarks/10-string-intern/.
*/
public final class RhinoStringPool {
/**
* The threadsafe datastructure that backs this pool.
*
*
We use weak-refs, rather than strong-refs, to prevent a memory leak in server-like
* applications.
*/
private static final Interner INTERNER = Interners.newWeakInterner();
/**
* Check if two strings are the same according to interning.
*
* The caller is responsible for ensuring that strings passed to this method are actually
* interned. This method mainly exists to highlight where equality checks depend on interning for
* correctness.
*
*
Ideally we could use something like a branded-type, for interned strings, to verify correct
* usage. However, Java doesn't support type-brands, and using like wrapper objects would
* undermine performance. This also needs to be ergonomic enough that callers don't resort to
* using `==` directly.
*/
public static boolean uncheckedEquals(String a, String b) {
return identical(a, b);
}
static String addOrGet(String s) {
return INTERNER.intern(s);
}
private RhinoStringPool() {}
}