eviction: fix Clock and CAWOLFU Evict to return correct keys before pooling; tests: add LRU, Clock, CAWOLFU eviction tests

Author: hyp3rd

pkg/eviction/cawolfu.go

@@ -67,10 +67,12 @@ func (c *CAWOLFU) Evict() (string, bool) {
 	if err == nil {
 		c.length--
 
+		// Preserve key before resetting the node for pool reuse
+		evictedKey := node.key
 		resetCAWOLFUNode(node)
 		c.nodePool.Put(node)
 
-		return node.key, true
+		return evictedKey, true
 	}
 	// If map/list out of sync, forcibly clean up
 	resetCAWOLFUNode(node)

pkg/eviction/cawolfu_test.go

@@ -0,0 +1,48 @@
+package eviction
+
+import "testing"
+
+func TestCAWOLFU_EvictsLeastFrequentTail(t *testing.T) {
+	c, err := NewCAWOLFU(2)
+	if err != nil {
+		t.Fatalf("NewCAWOLFU error: %v", err)
+	}
+
+	c.Set("a", 1)
+	c.Set("b", 2)
+	// bump 'a' so 'b' is less frequent
+	if _, ok := c.Get("a"); !ok {
+		t.Fatalf("expected to get 'a'")
+	}
+
+	// Insert 'c' -> evict tail ('b')
+	c.Set("c", 3)
+	if _, ok := c.Get("b"); ok {
+		t.Fatalf("expected 'b' to be evicted")
+	}
+	if _, ok := c.Get("a"); !ok {
+		t.Fatalf("expected 'a' to remain in cache")
+	}
+	if v, ok := c.Get("c"); !ok || v.(int) != 3 {
+		t.Fatalf("expected 'c'=3 in cache, got %v, ok=%v", v, ok)
+	}
+}
+
+func TestCAWOLFU_EvictMethodOrder(t *testing.T) {
+	c, err := NewCAWOLFU(2)
+	if err != nil {
+		t.Fatalf("NewCAWOLFU error: %v", err)
+	}
+
+	c.Set("a", 1)
+	c.Set("b", 2)
+	// Without additional access, tail is 'a' (inserted first with same count)
+	key, ok := c.Evict()
+	if !ok || key != "a" {
+		t.Fatalf("expected to evict 'a' first, got %q ok=%v", key, ok)
+	}
+	key, ok = c.Evict()
+	if !ok || key != "b" {
+		t.Fatalf("expected to evict 'b' second, got %q ok=%v", key, ok)
+	}
+}

pkg/eviction/clock.go

@@ -57,11 +57,13 @@ func (c *ClockAlgorithm) Evict() (string, bool) {
 		if item.AccessCount > 0 {
 			item.AccessCount--
 		} else {
-			delete(c.keys, item.Key)
+			// Preserve key before zeroing the item back to the pool
+			evictedKey := item.Key
+			delete(c.keys, evictedKey)
 			c.itemPoolManager.Put(item)
 			c.items[c.hand] = nil
 
-			return item.Key, true
+			return evictedKey, true
 		}
 
 		c.hand = (c.hand + 1) % c.capacity

pkg/eviction/clock_test.go

@@ -0,0 +1,43 @@
+package eviction
+
+import "testing"
+
+func TestClock_EvictsWhenHandFindsColdPage(t *testing.T) {
+	clk, err := NewClockAlgorithm(2)
+	if err != nil {
+		t.Fatalf("NewClockAlgorithm error: %v", err)
+	}
+
+	clk.Set("a", 1)
+	clk.Set("b", 2)
+
+	// Touch 'a' once to increment its AccessCount; leave 'b' cold
+	if _, ok := clk.Get("a"); !ok {
+		t.Fatalf("expected to get 'a'")
+	}
+
+	// Eviction may require multiple passes due to access count decrements.
+	// Loop until 'b' is evicted (within a few attempts).
+	var (
+		key string
+		ok  bool
+	)
+	for i := 0; i < 3; i++ {
+		key, ok = clk.Evict()
+		if ok && key == "b" {
+			break
+		}
+	}
+	if !ok || key != "b" {
+		t.Fatalf("expected to evict 'b' first within retries, got %q ok=%v", key, ok)
+	}
+
+	// Now evict the remaining 'a', possibly requiring one more pass.
+	key, ok = clk.Evict()
+	if !ok {
+		key, ok = clk.Evict()
+	}
+	if !ok || key != "a" {
+		t.Fatalf("expected to evict 'a' second, got %q ok=%v", key, ok)
+	}
+}

pkg/eviction/lru_test.go

@@ -0,0 +1,50 @@
+package eviction
+
+import "testing"
+
+func TestLRU_EvictsLeastRecentlyUsedOnSet(t *testing.T) {
+	lru, err := NewLRUAlgorithm(2)
+	if err != nil {
+		t.Fatalf("NewLRUAlgorithm error: %v", err)
+	}
+
+	lru.Set("a", 1)
+	lru.Set("b", 2)
+
+	// Access "a" so that "b" becomes the least recently used
+	if _, ok := lru.Get("a"); !ok {
+		t.Fatalf("expected to get 'a'")
+	}
+
+	// Insert "c"; should evict "b"
+	lru.Set("c", 3)
+	if _, ok := lru.Get("b"); ok {
+		t.Fatalf("expected 'b' to be evicted")
+	}
+	if _, ok := lru.Get("a"); !ok {
+		t.Fatalf("expected 'a' to remain in cache")
+	}
+	if v, ok := lru.Get("c"); !ok || v.(int) != 3 {
+		t.Fatalf("expected 'c'=3 in cache, got %v, ok=%v", v, ok)
+	}
+}
+
+func TestLRU_EvictMethodOrder(t *testing.T) {
+	lru, err := NewLRUAlgorithm(2)
+	if err != nil {
+		t.Fatalf("NewLRUAlgorithm error: %v", err)
+	}
+
+	lru.Set("a", 1)
+	lru.Set("b", 2)
+
+	// After two inserts, tail should be "a"
+	key, ok := lru.Evict()
+	if !ok || key != "a" {
+		t.Fatalf("expected to evict 'a' first, got %q ok=%v", key, ok)
+	}
+	key, ok = lru.Evict()
+	if !ok || key != "b" {
+		t.Fatalf("expected to evict 'b' second, got %q ok=%v", key, ok)
+	}
+}