expose read only view of thread local map of stacks

slf4j-api/src/main/java/org/slf4j/helpers/ImmutableDeque.java

@@ -0,0 +1,194 @@
+package org.slf4j.helpers;
+
+import java.util.Collection;
+import java.util.Deque;
+import java.util.Iterator;
+
+public class ImmutableDeque<T> implements Deque<T> {
+    Deque<T> deque;
+
+    public ImmutableDeque(Deque<T> deque) {
+        if (deque == null) {
+            throw new IllegalArgumentException();
+        }
+
+        this.deque = deque;
+    }
+    public static <T> ImmutableDeque<T> of(Deque<T> deque) {
+        return new ImmutableDeque<>(deque);
+    }
+    @Override
+    public void addFirst(T t) {
+        throw new UnsupportedOperationException();
+    }
+
+    @Override
+    public void addLast(T t) {
+        throw new UnsupportedOperationException();
+    }
+
+    @Override
+    public boolean offerFirst(T t) {
+        throw new UnsupportedOperationException();
+    }
+
+    @Override
+    public boolean offerLast(T t) {
+        throw new UnsupportedOperationException();
+    }
+
+    @Override
+    public T removeFirst() {
+        throw new UnsupportedOperationException();
+    }
+
+    @Override
+    public T removeLast() {
+        throw new UnsupportedOperationException();
+    }
+
+    @Override
+    public T pollFirst() {
+        throw new UnsupportedOperationException();
+    }
+
+    @Override
+    public T pollLast() {
+        throw new UnsupportedOperationException();
+    }
+
+    @Override
+    public T getFirst() {
+        return deque.getFirst();
+    }
+
+    @Override
+    public T getLast() {
+        return deque.getLast();
+    }
+
+    @Override
+    public T peekFirst() {
+        return deque.peekFirst();
+    }
+
+    @Override
+    public T peekLast() {
+        return deque.peekLast();
+    }
+
+    @Override
+    public boolean removeFirstOccurrence(Object o) {
+        throw new UnsupportedOperationException();
+    }
+
+    @Override
+    public boolean removeLastOccurrence(Object o) {
+        throw new UnsupportedOperationException();
+    }
+
+    @Override
+    public boolean add(T t) {
+        throw new UnsupportedOperationException();
+    }
+
+    @Override
+    public boolean offer(T t) {
+        throw new UnsupportedOperationException();
+    }
+
+    @Override
+    public T remove() {
+        throw new UnsupportedOperationException();
+    }
+
+    @Override
+    public T poll() {
+        throw new UnsupportedOperationException();
+    }
+
+    @Override
+    public T element() {
+        return deque.element();
+    }
+
+    @Override
+    public T peek() {
+        return deque.peek();
+    }
+
+    @Override
+    public boolean addAll(Collection<? extends T> collection) {
+        throw new UnsupportedOperationException();
+    }
+
+    @Override
+    public boolean removeAll(Collection<?> collection) {
+        throw new UnsupportedOperationException();
+    }
+
+    @Override
+    public boolean retainAll(Collection<?> collection) {
+        throw new UnsupportedOperationException();
+    }
+
+    @Override
+    public void clear() {
+        throw new UnsupportedOperationException();
+    }
+
+    @Override
+    public void push(T t) {
+        throw new UnsupportedOperationException();
+    }
+
+    @Override
+    public T pop() {
+        throw new UnsupportedOperationException();
+    }
+
+    @Override
+    public boolean remove(Object o) {
+        throw new UnsupportedOperationException();
+    }
+
+    @Override
+    public boolean containsAll(Collection<?> collection) {
+        return deque.containsAll(collection);
+    }
+
+    @Override
+    public boolean contains(Object o) {
+        return deque.contains(o);
+    }
+
+    @Override
+    public int size() {
+        return deque.size();
+    }
+
+    @Override
+    public boolean isEmpty() {
+        return deque.isEmpty();
+    }
+
+    @Override
+    public Iterator<T> iterator() {
+        return deque.iterator();
+    }
+
+    @Override
+    public Object[] toArray() {
+        return deque.toArray();
+    }
+
+    @Override
+    public <T1> T1[] toArray(T1[] array) {
+        return deque.toArray(array);
+    }
+
+    @Override
+    public Iterator<T> descendingIterator() {
+        return deque.descendingIterator();
+    }
+}

slf4j-api/src/main/java/org/slf4j/helpers/ThreadLocalMapOfStacks.java

@@ -1,9 +1,7 @@
 package org.slf4j.helpers;
 
-import java.util.ArrayDeque;
-import java.util.Deque;
-import java.util.HashMap;
-import java.util.Map;
+import java.util.*;
+import java.util.stream.Collectors;
 
 
 /**
@@ -65,6 +63,13 @@ public Deque<String> getCopyOfDequeByKey(String key) {
 
         return new ArrayDeque<String>(deque);
     }
+
+    public Map<String, Deque<String>> getReadOnlyView() {
+        Map<String, Deque<String>> mapOfImmutableDeques = tlMapOfStacks.get().entrySet().stream()
+                .collect(Collectors.toMap(Map.Entry::getKey, entry -> ImmutableDeque.of(entry.getValue())));
+
+        return Collections.unmodifiableMap(mapOfImmutableDeques);
+    }
 
     /**
      * Clear the deque(stack) referenced by 'key'.