multiple_contexts_sync.java

Context cx = Context.create("js");
Value jsCode = cx.eval("js", "(function(x,y) { return JSON.stringify({x:x,y:y}); })");

Thread thread = new Thread(new Runnable() {
  @Override
  public void run() {
    while (true) {
      synchronized (cx) {
        jsCode.execute(42,43).asString();
      }
    }
  }
});

thread.start();

while (true) {
  synchronized (cx) {
    jsCode.execute(44,45).asString();
  }
}