Best Practice for Busy Waiting in Java

[Alan Bateman]

On 16/06/2025 12:09, Markus KARG wrote:
>
>
> In case you MUST use busy-wait, apply the following rules:
>
>
> * NEVER have EMPTY busy-wait loops, but ALWAYS put Thread.onSpinWait() 
> into it. The performance drop is negligible but the CO2 footprint is 
> considerably smaller.
>
> * IF it is acceptable for the waiting thread to not have the 
> *absolute* maximum throughput, put Thread.yield() before 
> Thread.onSpinWait() in the busy-wait loop, so CPU cores are more 
> efficiently used.
>
> * Never use Thread.sleep() in busy-wait loops.
>
> * If possible, pin current thread to current CPU core to prevent 
> inefficient context switches.
>
> * ...more rules...
>
>
> THAT is what my question is targeting! :-)
>

It may be possible to provide some guidelines but I don't think they can 
be turned into rules, e.g. the NEVER example is challenged by methods 
that do atomic increment/add/etc. as this read+CAS in a tight loop. 
There are also examples that of tight loops to CAS an object to the add 
it to a list. The examples of onSpinWait in the JDK might give you some 
ideas, e.g. using it in conjunction with a max spin count before timed 
back off or parking. One thing to add to your list is virtual threads 
where it may be better to park rather than Thread.yield.

-Alan