Set cleanup interval by default resolves #2

README.md

@@ -49,13 +49,6 @@ For a more detailed guide, see [reference](https://pkg.go.dev/github.com/motoki3
 
 ## Supported cache backends (cache replacement policy)
 
-The default backend is the built-in map.
-This is ultra-lightweight, but does **not** evict items.
-You should only use the built-in map backend if your key's cardinality is finite,
-and you are comfortable holding **all** values in-memory.
-
-Otherwise, you should use LRU or 2Q backend which automatically evicts overflown items.
-
 - Built-in map (default)
 - LRU (Least Recently Used)
 - 2Q (Two Queue Cache)

cache.go

@@ -32,7 +32,7 @@ func New[K comparable, V any](replaceFn replaceFunc[K, V], freshFor, ttl time.Du
 		return nil, errors.New("freshFor cannot be longer than ttl")
 	}
 
-	config := defaultConfig()
+	config := defaultConfig(ttl)
 	for _, option := range options {
 		option(&config)
 	}

config.go

@@ -23,12 +23,16 @@ const (
 	cacheBackend2Q
 )
 
-func defaultConfig() cacheConfig {
+func defaultConfig(ttl time.Duration) cacheConfig {
+	cleanupInterval := 2 * ttl
+	if ttl == 0 {
+		cleanupInterval = 60 * time.Second
+	}
 	return cacheConfig{
 		enableStrictCoalescing: false,
 		backend:                cacheBackendMap,
 		capacity:               0,
-		cleanupInterval:        0,
+		cleanupInterval:        cleanupInterval,
 	}
 }
 
@@ -80,8 +84,13 @@ func EnableStrictCoalescing() CacheOption {
 
 // WithCleanupInterval specifies cleanup interval of expired items.
 //
-// Note that by default, a cache will be initialized without a cleaner.
-// Try tuning your cache size (and using non-map backend) before using this option.
+// Setting interval of 0 (or negative) will disable the cleaner.
+// This means if using non-evicting cache backend (that is, the default, built-in map backend),
+// the cache keeps holding key-value pairs indefinitely.
+// If cardinality of key is very large, this leads to memory leak.
+//
+// By default, a cleaner runs every once in 2x ttl (or every 60s if ttl == 0).
+// Try tuning your cache size (and using non-map backend) before tuning this option.
 // Using cleanup interval on a cache with many items may decrease the through-put,
 // since the cleaner has to acquire the lock to iterate through all items.
 func WithCleanupInterval(interval time.Duration) CacheOption {