How to measure the rotation of 4 shafts? ESP8266/ESP32/Atmega, SPI/I2C

Hello
I'm looking for ideas for measuring the speed of four shafts, impulses from the sensor 2 per revolution, revolutions in the order of 1000 - 3000 per minute.
Processors preferably ESP8266, ESP32 or Atmega, SPI or I2C display.
The circuit does not need to do anything apart from measuring, although initially I was thinking about speed regulation (voltage control 0 - 10V).
On the web I found only one article on the subject, an idea from Germany, I do not remember the exact method, but the processor was perpetually busy so regulation was inherently out of the question.
Two measurements are fairly simple, so two processors and a common display are left, it is probably possible to do this, maybe master with display and slave connected via I2C.
At the end you can wire the sensors from the shafts to one measurement input.
Do you have any ideas for a tachometer with four sensors?
Greetings

PiotrPitucha wrote:

but the processor was perpetually busy

Purely the example was a delay. Child's play.

PiotrPitucha wrote:

Have you got any ideas for a tachometer from four sensors?

As well as from one - as long as it's done right, i.e. using hardware capabilities (including counters) and on interrupts