go/kvmemcache/cache_test.go

package kvmemcache

import (
	"errors"
	"fmt"
	"sync"
	"testing"
	"time"
)

type State[K comparable] struct {
	Keys  []K
	Stats Stats
}

func (c *Cache[K,V]) assert(state State[K]) error {
	c.lock.Lock()
	defer c.lock.Unlock()

	if len(c.cache) != len(state.Keys) {
		return fmt.Errorf(
			"Expected %d keys but found %d.",
			len(state.Keys),
			len(c.cache))
	}

	for _, k := range state.Keys {
		if _, ok := c.cache[k]; !ok {
			return fmt.Errorf(
				"Expected key %v not found.",
				k)
		}
	}

	if c.stats.Hits != state.Stats.Hits {
		return fmt.Errorf(
			"Expected %d hits, but found %d.",
			state.Stats.Hits,
			c.stats.Hits)
	}

	if c.stats.Misses != state.Stats.Misses {
		return fmt.Errorf(
			"Expected %d misses, but found %d.",
			state.Stats.Misses,
			c.stats.Misses)
	}

	return nil
}

var ErrTest = errors.New("Hello")

func TestCache_basic(t *testing.T) {
	c := New(Config[string, string]{
		MaxSize: 4,
		TTL:     50 * time.Millisecond,
		Src: func(key string) (string, error) {
			if key == "err" {
				return "", ErrTest
			}
			return key, nil
		},
	})

	type testCase struct {
		name  string
		sleep time.Duration
		key   string
		evict bool
		state State[string]
	}

	cases := []testCase{
		{
			name: "get a",
			key:  "a",
			state: State[string]{
				Keys:  []string{"a"},
				Stats: Stats{Hits: 0, Misses: 1},
			},
		}, {
			name: "get a again",
			key:  "a",
			state: State[string]{
				Keys:  []string{"a"},
				Stats: Stats{Hits: 1, Misses: 1},
			},
		}, {
			name:  "sleep, then get a again",
			sleep: 55 * time.Millisecond,
			key:   "a",
			state: State[string]{
				Keys:  []string{"a"},
				Stats: Stats{Hits: 1, Misses: 2},
			},
		}, {
			name: "get b",
			key:  "b",
			state: State[string]{
				Keys:  []string{"a", "b"},
				Stats: Stats{Hits: 1, Misses: 3},
			},
		}, {
			name: "get c",
			key:  "c",
			state: State[string]{
				Keys:  []string{"a", "b", "c"},
				Stats: Stats{Hits: 1, Misses: 4},
			},
		}, {
			name: "get d",
			key:  "d",
			state: State[string]{
				Keys:  []string{"a", "b", "c", "d"},
				Stats: Stats{Hits: 1, Misses: 5},
			},
		}, {
			name: "get e",
			key:  "e",
			state: State[string]{
				Keys:  []string{"b", "c", "d", "e"},
				Stats: Stats{Hits: 1, Misses: 6},
			},
		}, {
			name: "get c again",
			key:  "c",
			state: State[string]{
				Keys:  []string{"b", "c", "d", "e"},
				Stats: Stats{Hits: 2, Misses: 6},
			},
		}, {
			name: "get err",
			key:  "err",
			state: State[string]{
				Keys:  []string{"c", "d", "e", "err"},
				Stats: Stats{Hits: 2, Misses: 7},
			},
		}, {
			name: "get err again",
			key:  "err",
			state: State[string]{
				Keys:  []string{"c", "d", "e", "err"},
				Stats: Stats{Hits: 3, Misses: 7},
			},
		}, {
			name:  "evict c",
			key:   "c",
			evict: true,
			state: State[string]{
				Keys:  []string{"d", "e", "err"},
				Stats: Stats{Hits: 3, Misses: 7},
			},
		}, {
			name: "reload-all a",
			key:  "a",
			state: State[string]{
				Keys:  []string{"a", "d", "e", "err"},
				Stats: Stats{Hits: 3, Misses: 8},
			},
		}, {
			name: "reload-all b",
			key:  "b",
			state: State[string]{
				Keys:  []string{"a", "b", "e", "err"},
				Stats: Stats{Hits: 3, Misses: 9},
			},
		}, {
			name: "reload-all c",
			key:  "c",
			state: State[string]{
				Keys:  []string{"a", "b", "c", "err"},
				Stats: Stats{Hits: 3, Misses: 10},
			},
		}, {
			name: "reload-all d",
			key:  "d",
			state: State[string]{
				Keys:  []string{"a", "b", "c", "d"},
				Stats: Stats{Hits: 3, Misses: 11},
			},
		}, {
			name: "read a again",
			key:  "a",
			state: State[string]{
				Keys:  []string{"b", "c", "d", "a"},
				Stats: Stats{Hits: 4, Misses: 11},
			},
		}, {
			name: "read e, evicting b",
			key:  "e",
			state: State[string]{
				Keys:  []string{"c", "d", "a", "e"},
				Stats: Stats{Hits: 4, Misses: 12},
			},
		},
	}

	for _, tc := range cases {
		time.Sleep(tc.sleep)
		if !tc.evict {
			val, err := c.Get(tc.key)
			if tc.key == "err" && err != ErrTest {
				t.Fatal(tc.name, val)
			}
			if tc.key != "err" && val != tc.key {
				t.Fatal(tc.name, tc.key, val)
			}
		} else {
			c.Evict(tc.key)
		}

		if err := c.assert(tc.state); err != nil {
			t.Fatal(err)
		}
	}
}

func TestCache_thunderingHerd(t *testing.T) {
	c := New(Config[string,string]{
		MaxSize: 4,
		Src: func(key string) (string, error) {
			time.Sleep(time.Second)
			return key, nil
		},
	})

	wg := sync.WaitGroup{}
	for i := 0; i < 16384; i++ {
		wg.Add(1)
		go func() {
			defer wg.Done()
			val, err := c.Get("a")
			if err != nil {
				panic(err)
			}
			if val != "a" {
				panic(err)
			}
		}()
	}

	wg.Wait()

	stats := c.Stats()
	if stats.Hits != 16383 || stats.Misses != 1 {
		t.Fatal(stats)
	}
}