test: introduce cache concurrency safety test

modules/cache/cache_test.go

@@ -5,13 +5,18 @@ package cache
 
 import (
 	"errors"
+	"fmt"
+	"math/rand"
+	"os"
+	"sync"
+	"sync/atomic"
 	"testing"
 	"time"
 
-	"code.forgejo.org/go-chi/cache"
 	"forgejo.org/modules/setting"
 	"forgejo.org/modules/test"
 
+	"code.forgejo.org/go-chi/cache"
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 )
@@ -166,3 +171,56 @@ func TestGetInt64(t *testing.T) {
 	assert.EqualValues(t, 100, data)
 	Remove("key")
 }
+
+func TestCacheConcurrencySafety(t *testing.T) {
+	createTestCache(t)
+
+	testRedisHost := os.Getenv("TEST_REDIS_SERVER")
+	if testRedisHost == "" {
+		t.Skip("only relevant for a remote redis host")
+	}
+
+	numTests := 20
+	numIncrements := 1000
+	for testCount := range numTests {
+		t.Run(fmt.Sprintf("attempt:%d", testCount), func(t *testing.T) {
+			var counter atomic.Int64
+			var wg sync.WaitGroup
+			var firstError atomic.Value
+
+			getFunc := func() (int64, error) {
+				lastValue := counter.Load()
+				time.Sleep(time.Duration(rand.Intn(20)) * time.Millisecond)
+				return lastValue, nil
+			}
+
+			for range numIncrements {
+				wg.Go(func() {
+					counterValue := counter.Add(1)
+					Remove(t.Name())
+					cachedValue, err := GetInt64(t.Name(), getFunc)
+					if err != nil {
+						firstError.CompareAndSwap(nil, fmt.Sprintf("cache error: %v", err))
+					} else if cachedValue < counterValue {
+						firstError.CompareAndSwap(nil, fmt.Sprintf("incremented to value %d but retrieved value %d from cache", counterValue, cachedValue))
+					}
+				})
+			}
+
+			wg.Wait()
+			require.EqualValues(t, numIncrements, counter.Load())
+			if err := firstError.Load(); err != nil {
+				t.Fatal(err)
+			}
+
+			// Without invalidating the cache, check what was last stored in it.
+			value, err := GetInt64(t.Name(), func() (int64, error) {
+				t.Fatal("getFunc should not be invoked")
+				return 0, errors.New("getFunc should not be invoked")
+			})
+
+			require.NoError(t, err)
+			assert.EqualValues(t, numIncrements, value)
+		})
+	}
+}