bench: separate benchmarks for Pick and PickSource

As discussed in #26, the changes in go1.21 will remove rand contention
when the (now deprecated) rand.Seed() is not called.

In order to check if this brings performance parity, start to benchmark
both Pick and PickSource functions in parallel, and no longer rand.Seed
in test init.

weightedrand_test.go

@@ -33,10 +33,6 @@ func Example() {
 * Tests
 *******************************************************************************/
 
-func init() {
- rand.Seed(time.Now().UTC().UnixNano()) // only necessary prior to go1.20
-}
-
 const (
  testChoices = 10
  testIterations = 1000000
@@ -246,6 +242,24 @@ func BenchmarkPick(b *testing.B) {
 }
 
 func BenchmarkPickParallel(b *testing.B) {
+ for n := BMMinChoices; n <= BMMaxChoices; n *= 10 {
+ b.Run(strconv.Itoa(n), func(b *testing.B) {
+ choices := mockChoices(n)
+ chooser, err := NewChooser(choices...)
+ if err != nil {
+ b.Fatal(err)
+ }
+ b.ResetTimer()
+ b.RunParallel(func(pb *testing.PB) {
+ for pb.Next() {
+ _ = chooser.Pick()
+ }
+ })
+ })
+ }
+}
+
+func BenchmarkPickSourceParallel(b *testing.B) {
  for n := BMMinChoices; n <= BMMaxChoices; n *= 10 {
  b.Run(strconv.Itoa(n), func(b *testing.B) {
  choices := mockChoices(n)