On Sun, 29 Aug 2021, at 10:45 PM, sansaid wrote:
> Hello,
>
> Does anybody know of some reference code or common patterns I can use to keep
> track of worker goroutines? For context, I want a user to be able to issue a
> "stop" command using a CLI tool which will prompt my server to gracefully
> terminate one of my workers.
>
> For example, when a user issues a "start" command through a CLI tool, this
> will signal my server to spawn a goroutine that perpetually runs and polls an
> HTTP endpoint until a user initiates a "stop" command. When the user issues a
> "stop" command through the same CLI tool, I want the server to be able to
> signal the goroutine to stop. Any reference code would be much appreciated!
>
> One approach I thought of was by passing a `context.WithCancel()` and holding
> a reference to the cancel function in a global map (with the worker ID as
> keys). When the user issues a "stop" command against the worker ID, another
> function is executed which calls the context's cancel function. Example code
> below (appreciate this is horrendously breaking a lot of rules, but I want to
> focus only on the elements around passing the cancel function around - happy
> to discuss anything else that is of concern to someone though):
>
> ```
> // invoked when a CLI start subcommand is issued to my main CLI tool
> func (w *WorkerGroup) Start(ctx context.Context, id string) {
> _, cancel := context.WithCancel(ctx)
>
> w.Workers.Lock()
> w.Workers[id] := cancel
> w.Workers.Unlock()
>
> go startWorker(id)
> }
>
> // invoked when a CLI stop subcommand is issued to my main CLI tool
> func (w *WorkerGroup) Stop(id string) {
> cancelWorker := w.Workers[id]
>
> cancelWorker()
> }
> ```
>
> I have read that passing a context's cancel function around is a bad idea,
> but in an example like this, is it justified?
Passing the cancel function is fine and storing it for use later is fine too.
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