an extremely naive question regarding synchronized...

[WhatMeWorry via Digitalmars-d-learn]

I was reading this fasciniating article:

https://davesdprogramming.wordpress.com/2013/05/06/low-lock-singletons/

And to quote a section of it:
-----------------------------------------------------
static MySingleton get() {
     synchronized {
       if (instance_ is null) {
         instance_ = new MySingleton;
       }
     }
     return instance_;
   }

Now, if Thread 1 calls get(), it has a chance to finish 
instantiating instance_ and storing a reference to it before 
Thread 2 checks whether instance_ is null.  There’s only one 
problem with this:  It comes at a huge performance cost 
(benchmarks forthcoming).  Entering a synchronized block is 
expensive.
-----------------------------------------------------

Why is the synchronized block so expensive?  Isn't it just doing 
one conditional and a new command?  Again, to my naive way of 
thinking, this seems like a very small blocking window.

And the graph shows 1B get() calls.  I assume B stands for 
billion.  What use case would require so many gets?

Thanks.