WIP: minigc package with StarSystem

minigc/minigc.go

@@ -0,0 +1,55 @@
+package minigc
+
+import (
+	"context"
+	"sync"
+
+	"github.com/vimeo/galaxycache/lru"
+)
+
+type HydrateCB[K comparable, V any] func(ctx context.Context, key K) (V, error)
+
+// StarSystem is an in-process cache intended for in-memory data
+// It's a thin wrapper around another cache implementation that takes care of
+// filling cache misses instead of requiring Add() calls.
+// Note: the underlying cache implementation may change at any time.
+type StarSystem[K comparable, V any] struct {
+	lru       lru.TypedCache[K, V]
+	hydrateCB HydrateCB[K, V]
+	mu        sync.Mutex
+}
+
+type StarSystemParams[K comparable, V any] struct {
+	// MaxEntries is the maximum number of cache entries before
+	// an item is evicted. Zero means no limit.
+	MaxEntries int
+
+	// OnEvicted optionally specificies a callback function to be
+	// executed when an typedEntry is purged from the cache.
+	OnEvicted func(key K, value V)
+}
+
+func NewStarSystem[K comparable, V any](cb HydrateCB[K, V], params StarSystemParams[K, V]) *StarSystem[K, V] {
+	return &StarSystem[K, V]{
+		hydrateCB: cb,
+		lru: lru.TypedCache[K, V]{
+			MaxEntries: params.MaxEntries,
+			OnEvicted:  params.OnEvicted,
+		},
+	}
+}
+
+func (s *StarSystem[K, V]) Get(ctx context.Context, key K) (V, error) {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+	if v, ok := s.lru.Get(key); ok {
+		return v, nil
+	}
+	val, hydErr := s.hydrateCB(ctx, key)
+	if hydErr != nil {
+		var zv V
+		return zv, hydErr
+	}
+	s.lru.Add(key, val)
+	return val, nil
+}