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.
