Scala lazy values : performance penalty? Threadsafe? [duplicate]

Answer 1

It is made thread-safe using double-checked locking http://code-o-matic.blogspot.com/2009/05/double-checked-locking-idiom-sweet-in.html Obviously this does mean that accessing lazy vals is slower than non-lazy ones.

Answer 2

UPDATE: OOPS, as Vasil pointed out, the question is a copy of another thread, and as it happens, so is this answer.

I took this class:

class Foo {
  lazy val test = "hi"
}

Compiled and decompiled (with jd-gui):

public class Foo
  implements ScalaObject
{
  private String test;
  public volatile int bitmap$0;

  public String test()
  {
    if (
      (this.bitmap$0 & 0x1) == 0);
    synchronized (this)
    {
      if (
        (this.bitmap$0 & 0x1) == 0) {
        this.test = "hi"; this.bitmap$0 |= 1; } return this.test;
    }
  }
}

As you can see it is using the double check paradigm with a volatile variable. So I think it is safe