Function TestNoDedup

groupcache_test.go:388–446

TestNoDedup tests invariants on the cache size when singleflight is unable to dedup calls.

(t *testing.T)

// TestNoDedup tests invariants on the cache size when singleflight is
// unable to dedup calls.
func TestNoDedup(t *testing.T) {
	const testkey = "testkey"
	const testval = "testval"
	g := newGroup("testgroup", 1024, GetterFunc(func(_ context.Context, key string, dest Sink) error {
		return dest.SetString(testval)
	}), nil)

	orderedGroup := &orderedFlightGroup{
		stage1: make(chan bool),
		stage2: make(chan bool),
		orig:   g.loadGroup,
	}
	// Replace loadGroup with our wrapper so we can control when
	// loadGroup.Do is entered for each concurrent request.
	g.loadGroup = orderedGroup

	// Issue two idential requests concurrently.  Since the cache is
	// empty, it will miss.  Both will enter load(), but we will only
	// allow one at a time to enter singleflight.Do, so the callback
	// function will be called twice.
	resc := make(chan string, 2)
	for i := 0; i < 2; i++ {
		go func() {
			var s string
			if err := g.Get(dummyCtx, testkey, StringSink(&s)); err != nil {
				resc <- "ERROR:" + err.Error()
				return
			}
			resc <- s
		}()
	}

	// Ensure both goroutines have entered the Do routine.  This implies
	// both concurrent requests have checked the cache, found it empty,
	// and called load().
	orderedGroup.stage1 <- true
	orderedGroup.stage1 <- true
	orderedGroup.stage2 <- true
	orderedGroup.stage2 <- true

	for i := 0; i < 2; i++ {
		if s := <-resc; s != testval {
			t.Errorf("result is %s want %s", s, testval)
		}
	}

	const wantItems = 1
	if g.mainCache.items() != wantItems {
		t.Errorf("mainCache has %d items, want %d", g.mainCache.items(), wantItems)
	}

	// If the singleflight callback doesn't double-check the cache again
	// upon entry, we would increment nbytes twice but the entry would
	// only be in the cache once.
	const wantBytes = int64(len(testkey) + len(testval))
	if g.mainCache.nbytes != wantBytes {
		t.Errorf("cache has %d bytes, want %d", g.mainCache.nbytes, wantBytes)
	}