semaphore in any operating system

[Daljeet12]

I am trying to understand what is semaphore in any operating system ?

a semaphore is a variable or abstract data type used to control access to a common resource by multiple threads and avoid critical section problems in a concurrent system such as a multitasking operating system

In multitasking Tasks can share resource such as CPU time, memory, data etc

 

[wwfeldman]

sounds like a way to handshake and establish communication and
then to break it off to allow the next "user" a chance

What is a semaphore?

What is a semaphore?

A semaphore is a programming concept that is frequently used to solve multi-threading problems. My question to the community: What is a semaphore and how do you use it?

stackoverflow.com

 

[betwixt]

That is correct, its a kind of flag to let one process know what another is doing so they don't interact with common elements or proceed before a result is ready.

For example: if process one is calculating coordinates for a plotter and process two is driving the X & Y motors, if they ran concurrently the motors could move before their final destination was known. A semaphore raised by process one would say "I'm still busy" and process two would look at it to know when it was safe to start moving.

Brian.