Android LruCache (Android 3.1) thread safety

Android LruCache (Android 3.1) Thread Safety

Android’s LruCache is a powerful tool for caching data in your applications. But with multiple threads accessing the cache, understanding thread safety is crucial to avoid potential issues like data corruption or inconsistent states.

Thread Safety in LruCache

LruCache in Android 3.1 is designed with thread safety in mind. This means that it can be accessed concurrently by multiple threads without causing data corruption.

Key Features for Thread Safety:

• Synchronized Methods: LruCache’s core methods like get(), put(), remove(), and evictAll() are synchronized. This ensures that only one thread can access the cache’s internal data structures at a time, preventing race conditions.
• Internal Locking: LruCache uses an internal lock to synchronize access to its internal data structures, providing atomicity for operations.
• Copy-on-Write: For operations like get(), LruCache makes a copy of the cached data before returning it to the caller. This ensures that modifications to the data by one thread don’t affect other threads.

Using LruCache in a Multi-Threaded Environment

While LruCache itself is thread-safe, you need to be careful when using it in a multi-threaded environment:

• Avoid Data Modification: While LruCache ensures data consistency, it’s best to avoid modifying data returned from get() directly, as it might affect the cached version. Always use a copy.
• Synchronized Access to External Data: If you’re using the cache to store references to objects that are modified outside the cache, you’ll need to ensure synchronized access to those objects.

Example: LruCache Usage in a Multi-Threaded Application

import android.util.LruCache;

public class ImageLoader {
  private LruCache imageCache;

  public ImageLoader() {
    // Cache size: 10 MB (adjust based on your memory constraints)
    imageCache = new LruCache<>(10 * 1024 * 1024);
  }

  public Bitmap loadImage(String imageUrl) {
    // Get from cache
    Bitmap bitmap = imageCache.get(imageUrl);

    // If not in cache, load from network
    if (bitmap == null) {
      // Network access should be performed in a background thread
      bitmap = loadFromNetwork(imageUrl);
      // Cache the loaded bitmap
      if (bitmap != null) {
        imageCache.put(imageUrl, bitmap);
      }
    }

    return bitmap;
  }

  private Bitmap loadFromNetwork(String imageUrl) {
    // Network operation implementation (replace with your actual network logic)
    // ...
    return null;
  }
}

Thread Safety Comparison Table

Conclusion

Android’s LruCache provides built-in thread safety, making it suitable for use in multi-threaded applications. While you need to be cautious about data modification and synchronized access to external data, LruCache effectively handles concurrent access, ensuring data integrity and consistent cache behavior.