weak_cache 2.0.0

Weak cache that uses weak references for holding values. Implements full Map interface including keys and values iteration.

Weak Cache

Weak cache is Map implementation that uses WeakReferences for holding values and Finalizer to manage it's storage.

This package is useful in cases when you want to hold an object in cache while it's in usage and accessible and remove it when it's no longer needed.

You can use it to cache data (e.g. API responses) for a small amount of time (until nex garbage collection cycle).

For example you can hold description object in cache while traversing deep into nested views and it eventually will be removed when you lose all references to it.

Features

• Uses WeakReference for storing values.
• Uses Finalizer to remove objects from internal storage.
• Allows you iterate over keys/values (while iterating, all stored values are temporarily made into strong references, to prevent concurrent edit of storage while iterating over it).
• Optimized containsValue via internal managed Expando.
• Implements full Map<K, V> interface.
• WeakCache itself can be safely garbage collected and doesn't produce memory leaks.

Usage

Just create cache, add some values, and they'll be removed when all other strong references to they are lost.

// ID - Object cache
final cache = WeakCache<int, Object>();

Object? obj = Object();
cache[0] = obj;
// ...
obj = null;
// ...
// After garbage collection cache[0] will be removed.
cache[0] == null;

See example for detailed test case.

Issues

If you encounter issues, here are some tips for debug, if nothing helps report to issue tracker on GitHub:

• It's possible that GC cycles are not yet touched objects and Finalizer is not executed it's callback.
• Check that your objects are not strongly references elsewhere.
• Set kDebug to true in lib/src/debug.dart.
  • Using iteration should eventually print Strong snapshot was garbage collected to console, lookout for messages like CacheMutex.unlock (was X) and CacheMutex.lock (was X) to track concurrent write locks status.
  • If you expect WeakCache to be destroyed by GC lookout for Mutex stream closed. message.
  • Try to feed memory like in example to force GC.