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
