fix: exit ticktock goroutine when pool is closed

[GlebRadchenko]

---

name: Pull request
about: Fixes a bug
title: 'fix ticktock memory leaks'
labels: ''
assignees: ''

1. Are you opening this pull request for bug-fixs, optimizations or new feature?

bugfix

2. Please describe how these code changes achieve your intention.

The fix enables ticktock goroutine to stop it's execution.

3. Please link to the relevant issues (if any).

#263

4. Which documentation changes (if any) need to be made/updated because of this PR?

4. Checklist

• I have squashed all insignificant commits.
• I have commented my code for explaining package types, values, functions, and non-obvious lines.
• I have written unit tests and verified that all tests passes (if needed).
• I have documented feature info on the README (only when this PR is adding a new feature).
• (optional) I am willing to help maintain this change if there are issues with it later.

[panjf2000]

I think the better way to do this is to use context and select in for loop, like purgeStaleWorkers() does.
So you should pass the context to ticktock() and use an atomic int32 to indicate whether ticktock() is done, handle these properly in ReleaseTimeout() and Reboot().

In short, just do what exactly purgeStaleWorkers() has already done.

[GlebRadchenko]

Addressed, but I'm still concerned if atomic int32 is helpful for ticktock case since there is no worker-related awaiting logic. lmk if you need anything else

[codecov]

Codecov Report

Base: 92.88% // Head: 93.17% // Increases project coverage by +0.28% 🎉

Coverage data is based on head (42086fe) compared to base (3fbd956).
Patch coverage: 97.14% of modified lines in pull request are covered.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #264      +/-   ##
==========================================
+ Coverage   92.88%   93.17%   +0.28%     
==========================================
  Files           9        9              
  Lines         759      791      +32     
==========================================
+ Hits          705      737      +32     
  Misses         41       41              
  Partials       13       13              

Flag	Coverage Δ
unittests	93.17% <97.14%> (+0.28%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
pool.go	90.49% <97.14%> (+0.67%)	⬆️
pool_func.go	91.88% <97.14%> (+0.50%)	⬆️

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[panjf2000]

LGTM