Cost of using weak references in Java

Question

Has anyone researched the runtime costs involved in creating and garbage collecting Java WeakReference objects? Are there any performance issues (e.g. contention) for multi

Answer 1

cache using weak references may significantly slow down your app if it's rebuild on demand e.g. in getters:

public Object getSomethingExpensiveToFind() {
    if(cache.contains(EXPENSIVE_OBJ_KEY)) {
        return cache.get(EXPENSIVE_OBJ_KEY);
    }

    Object sth = obtainSomethingExpensiveToFind(); // computationally expensive
    cache.put(EXPENSIVE_OBJ_KEY, sth);
    return sth;
} 

imagine this scenario:

1) app is running low on memory

2) GC cleans weak references, thus cache is cleared too

3) app continues, a lot of methods like getSomethingExpensiveToFind() are invoked and rebuild the cache

4) app is running low on memory again

5) GC cleans wear references, clears cache

6) app continues, a lot of methods like getSomethingExpensiveToFind() are invoked and rebuild the cache again

7) and so on...

I came upon such problem - the app was interrupted by GC very often and it compeletly defeated the whole point of caching.

In other words, if improperly managed, weak references can slow down your application.