Add another test, clean up add logic a bit

clock/clock.go

@@ -75,19 +75,18 @@ func (c *Cache[K, V]) Add(key K, val V) {
 			value: val,
 		})
 		c.indices[key] = len(c.buf) - 1
-		c.clockhand = (c.clockhand + 1) % len(c.buf)
-		return
-	}
-	// Full, evict by reference bit then replace
-	hand := c.clockhand
-	for c.touches[hand].Load() > 0 {
-		c.touches[hand].Add(-1)
-		hand = (hand + 1) % len(c.buf)
+	} else {
+		// Full, evict by reference bit then replace
+		for c.touches[c.clockhand].Load() > 0 {
+			c.touches[c.clockhand].Add(-1)
+			c.clockhand += 1 % len(c.buf)
+		}
+		c.Evict(c.buf[c.clockhand].key)
+		c.buf.insertAt(c.clockhand, key, val)
+		c.indices[key] = c.clockhand
+		c.touches[c.clockhand].Add(1)
 	}
-	c.Evict(c.buf[hand].key)
-	c.buf.insertAt(hand, key, val)
-	c.indices[key] = hand
-	c.clockhand = hand
+	c.clockhand = (c.clockhand + 1) % len(c.buf)
 }
 
 // Get returns the value for a given key, if present.

clock/clock_test.go

@@ -44,3 +44,96 @@ func TestCacheGet(t *testing.T) {
 		})
 	}
 }
+
+func TestCacheAdd(t *testing.T) {
+	tests := []struct {
+		name          string
+		size          int
+		keysToAdd     []string
+		valueToAdd    []string
+		expectedCache buffer[string, string]
+	}{
+		{
+			"beyond_capacity_evicts_first_untouched",
+			3,
+			[]string{"key-a", "key-b", "key-c", "key-d", "key-e"},
+			[]string{"val-a", "val-b", "val-c", "val-d", "val-e"},
+			buffer[string, string]{
+				&bufferItem[string, string]{key: "key-e", value: "val-e"},
+				&bufferItem[string, string]{key: "key-b", value: "val-b"},
+				&bufferItem[string, string]{key: "key-d", value: "val-d"},
+			},
+		},
+		{
+			"multiple_touches_decreases_eviction_chances",
+			3,
+			[]string{"key-a", "key-b", "key-c", "key-a", "key-a", "key-d", "key-e"},
+			[]string{"val-a", "val-b", "val-c", "val-a", "val-a", "val-d", "val-e"},
+			buffer[string, string]{
+				&bufferItem[string, string]{key: "key-a", value: "val-a"},
+				&bufferItem[string, string]{key: "key-e", value: "val-e"},
+				&bufferItem[string, string]{key: "key-d", value: "val-d"},
+			},
+		},
+	}
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			cache := New[string, string](test.size)
+			for i := 0; i < len(test.keysToAdd); i++ {
+				key := test.keysToAdd[i]
+				val := test.valueToAdd[i]
+				cache.Add(key, val)
+			}
+			for i := 0; i < len(cache.buf); i++ {
+				cachedKey := cache.buf[i].key
+				cachedValue := cache.buf[i].value
+				expectedKey := test.expectedCache[i].key
+				expectedValue := test.expectedCache[i].value
+				if cachedKey != expectedKey {
+					t.Fatalf("bad cache key; got %s, wanted %s at index %d", cachedKey, expectedKey, i)
+				}
+				if cachedValue != expectedValue {
+					t.Fatalf("bad cache value; got %s, wanted %s at index %d", cachedValue, expectedValue, i)
+				}
+			}
+		})
+	}
+}
+
+func BenchmarkGetAllHits(b *testing.B) {
+	b.ReportAllocs()
+	type complexStruct struct {
+		a, b, c, d, e, f int64
+		k, l, m, n, o, p float64
+	}
+	// Populate the cache
+	l := New[int, complexStruct](32)
+	for z := 0; z < 32; z++ {
+		l.Add(z, complexStruct{a: int64(z)})
+	}
+
+	b.ResetTimer()
+	for z := 0; z < b.N; z++ {
+		// take the lower 5 bits as mod 32 so we always hit
+		l.Get(z & 31)
+	}
+}
+
+func BenchmarkGetHalfHits(b *testing.B) {
+	b.ReportAllocs()
+	type complexStruct struct {
+		a, b, c, d, e, f int64
+		k, l, m, n, o, p float64
+	}
+	// Populate the cache
+	l := New[int, complexStruct](32)
+	for z := 0; z < 32; z++ {
+		l.Add(z, complexStruct{a: int64(z)})
+	}
+
+	b.ResetTimer()
+	for z := 0; z < b.N; z++ {
+		// take the lower 4 bits as mod 16 shifted left by 1 to
+		l.Get((z&15)<<1 | z&16>>4 | z&1<<4)
+	}
+}