java - Nashorn 中的评估函数是否可从不同线程重用？

Question

是否有可能为所有 servlet 请求重用同一个 Nashorn 引擎和同一个 JavaScriptObject，它作为 JS 函数的评估结果，如果该函数不更改任何共享对象而仅使用调用时给出的参数？看下面的例子:

public class MyServlet extends HttpServlet {

private ScriptEngineManager factory;
private ScriptEngine engine;
private ScriptObjectMirror script;

@Override
public void init() throws ServletException {
    try {
        factory = new ScriptEngineManager();
        engine = factory.getEngineByName("nashorn");
        script = (ScriptObjectMirror)engine.eval("function(writer) {writer.print('Hello, World!');}");
    } catch (ScriptException ex) {
        Logger.getLogger(MyServlet.class.getName()).log(Level.SEVERE, null, ex);
    }
}

@Override
public void doGet(HttpServletRequest req, HttpServletResponse res) throws IOException {
    try (PrintWriter writer = res.getWriter()) {
        script.call(null, writer);
        writer.close();
    } catch (IOException ex) {
        Logger.getLogger(MyServlet.class.getName()).log(Level.SEVERE, null, ex);
    }
}

这是线程安全的吗？这是 Reuse Nashorn ScriptEngine in Servlet 的后续行动

编辑:我不确定这对手头的问题有什么不同，但为了关注更有趣的问题，在什么情况下调用已评估的 js 函数是线程保存，我现在将所有字段设置为 final。所以代码是:

public class MyServlet extends HttpServlet {

final private ScriptEngineManager factory;
final private ScriptEngine engine;
final private ScriptObjectMirror script;

public MyServlet() {
    factory = new ScriptEngineManager();
    engine = factory.getEngineByName("nashorn");
    ScriptObjectMirror _script = null;
    try {
        _script = (ScriptObjectMirror) engine.eval("function(writer) {writer.print('Hello, World!');}");
    } catch (ScriptException ex) {
        Logger.getLogger(MyServlet.class.getName()).log(Level.SEVERE, null, ex);
    }
    script = _script;
}

@Override
public void init() throws ServletException {
}

@Override
public void doGet(HttpServletRequest req, HttpServletResponse res) throws IOException {
    try (PrintWriter writer = res.getWriter()) {
        script.call(null, writer);
        writer.close();
    } catch (IOException ex) {
        Logger.getLogger(MyServlet.class.getName()).log(Level.SEVERE, null, ex);
    }
}

Answer 1

你的实例变量都不是 safely published,所以这是一个很大的“不”。也没有 documentation说您使用的类是线程安全的，因此如果没有进一步的文档说明不同，您必须假设它们不是线程安全的。

回答:没有。