Goroutines and APIs

Go programming notes

November 18, 2019

Goroutines are a unusual and powerful programming language feature, so they are a tempting toy to play with, and they get a bit overused.

There is some indication that the following Go principle holds true:

Strive to provide synchronous APIs,  let the caller start goroutines.

To put this advice into a more concrete code example:

Do this:

func (t *type) Run(ctx context.Context) {
    // Implementation of background task
}

Instead of this:

func (t *type) Start() {
    t.wg.Add(1)
    go func() {
      // Implementation of background task
      t.wg.Done()
    }
}

func (t *type) Cancel() {
    // Somehow cancel the background task
    t.wg.Wait()
}

Upsides for Run() :

• The caller gets to decide how the “background” code gets run.

  go
  

• Background task cancellation is provided through the context.
• Waiting for the background task has a trivial API (when the function returns), and can be done with the mechanism the caller prefers (waitgroups, channels, …)
• It’s on the safe side API-wise: There is no Close() method which callers can forget to call (leaking resources).

Another great discussion of this was in the Go Time: On application design podcast (starting around minute 47, Mat Ryer’s explanation really resonated with me)