fix(solver) resolve a data race with ops counters

[hbagdi]

No description provided.

[codecov-commenter]

Codecov Report

Merging #381 (1861bbe) into main (729559e) will decrease coverage by 7.51%.
The diff coverage is 30.43%.

@@            Coverage Diff             @@
##             main     #381      +/-   ##
==========================================
- Coverage   54.19%   46.68%   -7.52%     
==========================================
  Files          61       87      +26     
  Lines        4971     6568    +1597     
==========================================
+ Hits         2694     3066     +372     
- Misses       1978     3136    +1158     
- Partials      299      366      +67     

Impacted Files	Coverage Δ
cmd/common.go	0.00% <0.00%> (ø)
cmd/common_konnect.go	16.79% <0.00%> (+1.57%)	⬆️
solver/solver.go	8.88% <46.66%> (ø)
cmd/validate.go	20.00% <0.00%> (-3.34%)	⬇️
cmd/root.go	52.73% <0.00%> (-3.23%)	⬇️
cmd/konnect_diff.go	75.00% <0.00%> (-2.78%)	⬇️
cmd/konnect_dump.go	25.37% <0.00%> (-1.72%)	⬇️
cmd/dump.go	24.79% <0.00%> (-1.59%)	⬇️
cmd/konnect_sync.go	70.00% <0.00%> (-1.43%)	⬇️
... and 39 more

---

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[hbagdi]

Had a conversation with @mflendrich on this and updated the code to use a mutex instead of atomic as that package has a ton of gotchas.

[mflendrich]

nit - Count might be a better name because it describes the returned value better, and because Read is already in use by io.Reader.

[mflendrich]

optional: too see any meaningful risk of race condition occuring, you probably need each of the goroutines to increment the counter 1000 times in a loop.

[hbagdi]

This is really to trigger a data race bug with go test -race.
If we disable locking, this reliably produces the race:

go test -race
==================
WARNING: DATA RACE
Read at 0x00c000156240 by goroutine 9:
  github.com/kong/deck/solver.(*AtomicInt32Counter).Increment()
      /home/hbagdi/deck/solver/solver.go:31 +0x6f
  github.com/kong/deck/solver.TestStats_CreateOps.func1()
      /home/hbagdi/deck/solver/solver_test.go:18 +0x66

Previous write at 0x00c000156240 by goroutine 8:
  github.com/kong/deck/solver.(*AtomicInt32Counter).Increment()
      /home/hbagdi/deck/solver/solver.go:31 +0x84
  github.com/kong/deck/solver.TestStats_CreateOps.func1()
      /home/hbagdi/deck/solver/solver_test.go:18 +0x66

Goroutine 9 (running) created at:
  github.com/kong/deck/solver.TestStats_CreateOps()
      /home/hbagdi/deck/solver/solver_test.go:16 +0xf2
  testing.tRunner()
      /usr/local/go/src/testing/testing.go:1194 +0x202

Goroutine 8 (finished) created at:
  github.com/kong/deck/solver.TestStats_CreateOps()
      /home/hbagdi/deck/solver/solver_test.go:16 +0xf2
  testing.tRunner()
      /usr/local/go/src/testing/testing.go:1194 +0x202
==================
--- FAIL: TestStats_CreateOps (0.00s)
    testing.go:1093: race detected during execution of test
FAIL
exit status 1
FAIL    github.com/kong/deck/solver     0.008s