Handle resource changes when the resources is already evicted from cache

Also fix a logical flaw in the cache resizer that made it too aggressive. After this I haven't been able to reproduce #11988, but I need to look closer.

Closes #11973
Updates #11988

1 files changed, 67 insertions, 0 deletions

diff --git a/common/collections/stack.go b/common/collections/stack.go
new file mode 100644
index 000000000..0f1581626
--- /dev/null
+++ b/common/collections/stack.go
@@ -0,0 +1,67 @@
+// Copyright 2024 The Hugo Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package collections
+
+import "sync"
+
+// Stack is a simple LIFO stack that is safe for concurrent use.
+type Stack[T any] struct {
+	items []T
+	zero  T
+	mu    sync.RWMutex
+}
+
+func NewStack[T any]() *Stack[T] {
+	return &Stack[T]{}
+}
+
+func (s *Stack[T]) Push(item T) {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+	s.items = append(s.items, item)
+}
+
+func (s *Stack[T]) Pop() (T, bool) {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+	if len(s.items) == 0 {
+		return s.zero, false
+	}
+	item := s.items[len(s.items)-1]
+	s.items = s.items[:len(s.items)-1]
+	return item, true
+}
+
+func (s *Stack[T]) Peek() (T, bool) {
+	s.mu.RLock()
+	defer s.mu.RUnlock()
+	if len(s.items) == 0 {
+		return s.zero, false
+	}
+	return s.items[len(s.items)-1], true
+}
+
+func (s *Stack[T]) Len() int {
+	s.mu.RLock()
+	defer s.mu.RUnlock()
+	return len(s.items)
+}
+
+func (s *Stack[T]) Drain() []T {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+	items := s.items
+	s.items = nil
+	return items
+}