How to make a select case non-blocking in for loop without default

Question

I have this piece of code.

func Start() bool {
    for {
        if checkSomthingIsTrue() {
            if err := doSomthing(); err != nil {
                continue
            }
        }
        select {
        case <-ctx.Done():
            return true
        }
    }
}

How to make the above function non blocking without using default: case. reason to not use default case is because its eating up 100% CPU always.

Answer: I have used time.Ticker to throttle Thanks

Answer 1

There is a fundamental misunderstanding here. A thread can do only two things:

• A thread can block, waiting for something.

• A thread can run, using CPU.

If a thread never blocks, then it uses 100% of the available CPU. You cannot make non-blocking code use less than 100% of the available CPU.

You have three options:

1. Use non-blocking code, and accept the 100% CPU usage.

2. Redesign checkSomthingIsTrue() so it uses a channel, and can be put inside the select block.

   for {
       select {
       case <-ctx.Done():
           return true
       case <-whenSomethingIsTrue():
           if err := doSomthing(); err != nil {
               continue
           }
       }
   }
   

3. Use a timeout to throttle the loop, for example:

   // Poll every 100ms.
   const pollInterval = 100 * time.Millisecond
   for {
       select {
       case <-ctx.Done():
           return true
       case <-time.After(pollInterval):
           if checkSomthingIsTrue() {
               if err := doSomthing(); err != nil {
                   continue
               }
           }
       }
   }
   

Also note that continue makes no sense, but that is a different issue.