[chore][processort/tailsamplingprocessor] Limit concurrency for certa…

…in tests (flay test on Windows runners) (open-telemetry#29014)

**Description:**
Limit number of goroutines started during
`processor/tailsamplingprocessor` tests. This causes very frequently
failures on the Windows tests, see
[here](open-telemetry#28682 (comment))
for example.

The issue is that the race detector has a hard limit on number of
goroutines, see golang/go#23611. The fix
limits the concurrency in two tests so this limit is not hit on GH
Windows runners.

**Link to tracking Issue:** 
Fix open-telemetry#9126

**Testing:**
Increased the concurrency on the two changed tests caused the error and
validated that it passed twice on my fork.

**Documentation:**
N/A

processor/tailsamplingprocessor/internal/idbatcher/id_batcher_test.go

@@ -103,11 +103,17 @@ func concurrencyTest(t *testing.T, numBatches, newBatchesInitialCapacity, batchC
 
 	ids := generateSequentialIds(10000)
 	wg := &sync.WaitGroup{}
+	// Limit the concurrency here to avoid creating too many goroutines and hit
+	// https://github.com/open-telemetry/opentelemetry-collector-contrib/issues/9126
+	concurrencyLimiter := make(chan struct{}, 128)
+	defer close(concurrencyLimiter)
 	for i := 0; i < len(ids); i++ {
 		wg.Add(1)
+		concurrencyLimiter <- struct{}{}
 		go func(id pcommon.TraceID) {
 			batcher.AddToCurrentBatch(id)
 			wg.Done()
+			<-concurrencyLimiter
 		}(ids[i])
 	}
 

processor/tailsamplingprocessor/processor_test.go

@@ -208,16 +208,24 @@ func TestConcurrentTraceArrival(t *testing.T) {
 		require.NoError(t, tsp.Shutdown(context.Background()))
 	}()
 
+	// Limit the concurrency here to avoid creating too many goroutines and hit
+	// https://github.com/open-telemetry/opentelemetry-collector-contrib/issues/9126
+	concurrencyLimiter := make(chan struct{}, 128)
+	defer close(concurrencyLimiter)
 	for _, batch := range batches {
 		// Add the same traceId twice.
 		wg.Add(2)
+		concurrencyLimiter <- struct{}{}
 		go func(td ptrace.Traces) {
 			require.NoError(t, tsp.ConsumeTraces(context.Background(), td))
 			wg.Done()
+			<-concurrencyLimiter
 		}(batch)
+		concurrencyLimiter <- struct{}{}
 		go func(td ptrace.Traces) {
 			require.NoError(t, tsp.ConsumeTraces(context.Background(), td))
 			wg.Done()
+			<-concurrencyLimiter
 		}(batch)
 	}