多线程Nashorn：o.constructor === o.constructor给出false

问题描述

我正在Nashorn中尝试加载和评估多线程脚本并获得一些令人震惊的行为：

I'm experimenting with multi-threaded scripts loading and evaluation in Nashorn and get kind of shocking behavior:

// having some object o loaded in another thread
print(o.constructor === o.constructor); // false
print(o.constructor === Object); // false as well
print(o.foo === o.foo); // true - OK

如何在单个脚本引擎中实现这一点？上面的 o 只是使用对象文字表示法创建的对象（在另一个线程中）。打印 o.constructor 给出通常的函数Object（）{[native code]}; 。

How can this be possible within single script engine? o above is just an object created using object literal notation (in another thread). Printing o.constructor gives usual function Object() { [native code] };.

同时：

print({}.constructor === {}.constructor); // true

任何想法？

更新

事实证明这与多线程完全无关。有关详细信息，请参阅下面的答案。

It turned out this was unrelated to multi-threading at all. See my answer below for details.

推荐答案

事实证明，这与多线程无关。这是一个简单的Scala程序，可以重现问题：

It turned out this does not relate to multi-threading at all. Here is a simple Scala program which reproduces the problem:

object Test extends App {
  val engine = new ScriptEngineManager().getEngineByName("nashorn")
  var o = engine.eval("({ foo: 'bar' })")
  var result = engine.eval("(o.constructor === o.constructor)", new SimpleBindings() {
    put("o", o)
  })
  print(result) // false
}

我错误地使用绑定参数。相反，我应该采用现有的绑定并就地更新它们。我仍然不相信这会导致 o.constructor === o.constructor 为假，但至少它现在有效。更正版本：

I was using bindings parameter incorrectly. Instead, I should take existing bindings and update 'em in-place. I'm still not convinced this should result in o.constructor === o.constructor to be false, but at least it works now. Corrected version:

object Test extends App {
  val engine = new ScriptEngineManager().getEngineByName("nashorn")
  var o = engine.eval("({ foo: 'bar' })")

  val bindings =  engine.getBindings(ScriptContext.ENGINE_SCOPE)
  bindings.put("o", o)

  var result = engine.eval("(o.constructor === o.constructor)", bindings)
  print(result) // true
}

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