From d53a86923570d403b6bd9157cf66b1396dde6393 Mon Sep 17 00:00:00 2001
From: "J. David Lee" <johnl@crumpington.com>
Date: Tue, 6 Apr 2021 17:51:16 +0200
Subject: [PATCH] kvmemcache: tests complete

---
 kvmemcache/cache.go      |  2 +-
 kvmemcache/cache_test.go | 78 ++++++++++++++++++++++++++++++++++------
 kvmemcache/internal.go   | 10 +++---
 3 files changed, 74 insertions(+), 16 deletions(-)

diff --git a/kvmemcache/cache.go b/kvmemcache/cache.go
index eea9b90..b451913 100644
--- a/kvmemcache/cache.go
+++ b/kvmemcache/cache.go
@@ -47,7 +47,7 @@ func New(conf Config) *Cache {
 }
 
 func (c *Cache) Get(key string) (interface{}, error) {
-	val, err, ok := c.get(key)
+	ok, val, err := c.get(key)
 	if ok {
 		return val, err
 	}
diff --git a/kvmemcache/cache_test.go b/kvmemcache/cache_test.go
index a9eb5b4..2231ebb 100644
--- a/kvmemcache/cache_test.go
+++ b/kvmemcache/cache_test.go
@@ -3,6 +3,7 @@ package kvmemcache
 import (
 	"errors"
 	"fmt"
+	"sync"
 	"testing"
 	"time"
 )
@@ -48,15 +49,15 @@ func (c *Cache) assert(state State) error {
 	return nil
 }
 
-var TestError = errors.New("Hello")
+var ErrTest = errors.New("Hello")
 
-func TestCache_Basic(t *testing.T) {
+func TestCache_basic(t *testing.T) {
 	c := New(Config{
 		MaxSize: 4,
 		TTL:     50 * time.Millisecond,
 		Src: func(key string) (interface{}, error) {
 			if key == "err" {
-				return nil, TestError
+				return nil, ErrTest
 			}
 			return key, nil
 		},
@@ -66,6 +67,7 @@ func TestCache_Basic(t *testing.T) {
 		name  string
 		sleep time.Duration
 		key   string
+		evict bool
 		state State
 	}
 
@@ -127,17 +129,43 @@ func TestCache_Basic(t *testing.T) {
 				Keys:  []string{"b", "c", "d", "e"},
 				Stats: Stats{Hits: 2, Misses: 6},
 			},
+		}, {
+			name: "get err",
+			key:  "err",
+			state: State{
+				Keys:  []string{"c", "d", "e", "err"},
+				Stats: Stats{Hits: 2, Misses: 7},
+			},
+		}, {
+			name: "get err again",
+			key:  "err",
+			state: State{
+				Keys:  []string{"c", "d", "e", "err"},
+				Stats: Stats{Hits: 3, Misses: 7},
+			},
+		}, {
+			name:  "evict c",
+			key:   "c",
+			evict: true,
+			state: State{
+				Keys:  []string{"d", "e", "err"},
+				Stats: Stats{Hits: 3, Misses: 7},
+			},
 		},
 	}
 
 	for _, tc := range cases {
 		time.Sleep(tc.sleep)
-		val, err := c.Get(tc.key)
-		if tc.key == "err" && err != TestError {
-			t.Fatal(tc.name, val)
-		}
-		if tc.key != "err" && val.(string) != tc.key {
-			t.Fatal(tc.name, tc.key, val)
+		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.(string) != tc.key {
+				t.Fatal(tc.name, tc.key, val)
+			}
+		} else {
+			c.Evict(tc.key)
 		}
 
 		if err := c.assert(tc.state); err != nil {
@@ -146,4 +174,34 @@ func TestCache_Basic(t *testing.T) {
 	}
 }
 
-// TODO: Test thundering herd mitigation.
+func TestCache_thunderingHerd(t *testing.T) {
+	c := New(Config{
+		MaxSize: 4,
+		Src: func(key string) (interface{}, error) {
+			time.Sleep(time.Second)
+			return key, nil
+		},
+	})
+
+	wg := sync.WaitGroup{}
+	for i := 0; i < 1024; 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 != 1023 || stats.Misses != 1 {
+		t.Fatal(stats)
+	}
+}
diff --git a/kvmemcache/internal.go b/kvmemcache/internal.go
index ea4efee..693dc1e 100644
--- a/kvmemcache/internal.go
+++ b/kvmemcache/internal.go
@@ -30,24 +30,24 @@ func (c *Cache) evict(key string) {
 	}
 }
 
-func (c *Cache) get(key string) (val interface{}, err error, ok bool) {
+func (c *Cache) get(key string) (ok bool, val interface{}, err error) {
 	c.lock.Lock()
 	defer c.lock.Unlock()
 
 	li := c.cache[key]
 	if li == nil {
-		return nil, nil, false
+		return false, nil, nil
 	}
 
 	item := li.Value.(lruItem)
 	// Maybe evict.
 	if c.ttl != 0 && time.Since(item.createdAt) > c.ttl {
 		c.evict(key)
-		return nil, nil, false
+		return false, nil, nil
 	}
 
 	c.stats.Hits++
-	return item.value, item.err, true
+	return true, item.value, item.err
 }
 
 func (c *Cache) load(key string) (interface{}, error) {
@@ -55,7 +55,7 @@ func (c *Cache) load(key string) (interface{}, error) {
 	defer c.updateLock.Unlock(key)
 
 	// Check again in case we lost the update race.
-	val, err, ok := c.get(key)
+	ok, val, err := c.get(key)
 	if ok {
 		return val, err
 	}