Fix flaky TestReusableGoroutinesPool test (#596)

.github/workflows/find-flaky-tests.yml

@@ -12,3 +12,5 @@ jobs:
       matrix:
         runs: [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20] # Run the build workflow 20 times
     uses: ./.github/workflows/test-build.yml
+    with:
+      concurrency-group: '-find-flaky-tests-${{ matrix.runs }}'

.github/workflows/test-build.yml

@@ -5,12 +5,16 @@ on:
       - main
   pull_request:
   workflow_call:
+    inputs:
+      concurrency-group:
+        required: true
+        type: string
 
 concurrency:
   # Cancel any running workflow for the same branch when new commits are pushed.
   # We group both by ref_name (available when CI is triggered by a push to a branch/tag)
   # and head_ref (available when CI is triggered by a PR).
-  group: "${{ github.ref_name }}-${{ github.head_ref }}"
+  group: "${{ github.ref_name }}-${{ github.head_ref }}${{ inputs.concurrency-group }}"
   cancel-in-progress: true
 
 jobs:

concurrency/worker_test.go

@@ -1,48 +1,61 @@
 package concurrency
 
 import (
+	"regexp"
 	"runtime"
+	"strings"
 	"testing"
 	"time"
 
 	"github.com/stretchr/testify/require"
 )
 
 func TestReusableGoroutinesPool(t *testing.T) {
-	baseGoroutines := runtime.NumGoroutine()
-	const workers = 2
+	buf := make([]byte, 1<<20)
+	buf = buf[:runtime.Stack(buf, false)]
+	testGoroutine := regexp.MustCompile(`goroutine (\d+) \[running\]:`).FindSubmatch(buf)[1]
+	require.NotEmpty(t, testGoroutine, "test goroutine not found")
+
+	countGoroutines := func() int {
+		buf := make([]byte, 1<<20)
+		buf = buf[:runtime.Stack(buf, true)]
+		// Count the number of goroutines created by this test
+		// This ensures that the test isn't affected by leaked goroutines from other tests.
+		return strings.Count(string(buf), " in goroutine "+string(testGoroutine))
+	}
 
-	w := NewReusableGoroutinesPool(workers)
-	require.Equal(t, baseGoroutines+workers, runtime.NumGoroutine())
+	const workerCount = 2
+	w := NewReusableGoroutinesPool(workerCount)
+	require.Equal(t, workerCount, countGoroutines())
 
 	// Wait a little bit so both goroutines would be waiting on the jobs chan.
 	time.Sleep(10 * time.Millisecond)
 
 	ch := make(chan struct{})
 	w.Go(func() { <-ch })
-	require.Equal(t, baseGoroutines+workers, runtime.NumGoroutine())
+	require.Equal(t, workerCount, countGoroutines())
 	w.Go(func() { <-ch })
-	require.Equal(t, baseGoroutines+workers, runtime.NumGoroutine())
+	require.Equal(t, workerCount, countGoroutines())
 	w.Go(func() { <-ch })
-	require.Equal(t, baseGoroutines+workers+1, runtime.NumGoroutine())
+	require.Equal(t, workerCount+1, countGoroutines())
 
 	// end workloads, we should have only the workers again.
 	close(ch)
 	for i := 0; i < 1000; i++ {
-		if runtime.NumGoroutine() == baseGoroutines+workers {
+		if countGoroutines() == workerCount {
 			break
 		}
 		time.Sleep(time.Millisecond)
 	}
-	require.Equal(t, baseGoroutines+workers, runtime.NumGoroutine())
+	require.Equal(t, workerCount, countGoroutines())
 
 	// close the workers, eventually they should be gone.
 	w.Close()
 	for i := 0; i < 1000; i++ {
-		if runtime.NumGoroutine() == baseGoroutines {
+		if countGoroutines() == 0 {
 			return
 		}
 		time.Sleep(time.Millisecond)
 	}
-	t.Fatalf("expected %d goroutines after closing, got %d", baseGoroutines, runtime.NumGoroutine())
+	t.Fatalf("expected %d goroutines after closing, got %d", 0, countGoroutines())
 }