Is there no way to iterate over or copy all the values of a Java ThreadLocal?

Question

Context:

static ThreadLocal threadLocalMyType = ...

What i\'d like is to say something like:

for (ThreadLoc         


        

Answer 1

I came acrosss the same problem and after seeing the answers here, I decided to use a hybrid approach:

public class PersistentThreadLocal extends ThreadLocal {

    final Map allValues;
    final Supplier valueGetter;

    public PersistentThreadLocal(Supplier initialValue) {
        this(0, initialValue);
    }

    public PersistentThreadLocal(int numThreads, Supplier initialValue) {
        allValues = Collections.synchronizedMap(
            numThreads > 0 ? new WeakHashMap<>(numThreads) : new WeakHashMap<>()
        );
        valueGetter = initialValue;
    }

    @Override
    protected T initialValue() {
        T value = valueGetter != null ? valueGetter.get() : super.initialValue();
        allValues.put(Thread.currentThread(), value);
        return value;
    }

    @Override
    public void set(T value) {
        super.set(value);
        allValues.put(Thread.currentThread(), value);
    }

    @Override
    public void remove() {
        super.remove();
        allValues.remove(Thread.currentThread());
    }

    public Collection getAll() {
        return allValues.values();
    }

    public void clear() {
        allValues.clear();
    }
}

EDIT: if you plan to use this with a ThreadPoolExecutor, change the WeakHashMap to a regular HashMap, otherwise strange things will happen!