TimerWheel.java why long mask = SPANS[index] - 1;

[javakinglzh]

TimerWheel.java line 129 why long mask = SPANS[index] - 1; why not long mask = SPANS[index] - 1;
can not understand

[ben-manes]

Hi @javakinglzh,

You accidentally asked why X and not X? Can you please clarify.

In case it helps (but you might know this):
The mask is a cheap version of a modulus operand, which is otherwise a division instruction (a multi-cycle arithmetic operation). In the case of a power-of-two this can be replaced with a single cycle AND instruction, x mod 2^i = x & (2^i – 1). This technique is popular in hash tables, including Java's, which improves performance due to how frequently they are used.

[ben-manes]

fyi, for your test case the proposed code changes passes.

[javakinglzh]

My computer has watchdog, I can not push code to github or submit PR.
You can make a fix.
With my best honest.

[ben-manes]

Thanks. I have a patch locally which handles this bug and for when the clock overflows. I'll try to wrap it up over the weekend or so, as its been hard to get focus for this project.

[ben-manes]

timerWheel.patch.txt

[ben-manes]

Released in 2.9.1 and 3.0.2