Use ConcurrentHashMap for cache.

As the normal maps are not using a ConcurrentHashMap it is
likely unnecessary as well that I am not aware of a
multi-threaded access.
But as it does not show any difference in performance
it is likely the bit more safe option.

core/src/main/java/bisq/core/account/sign/SignedWitnessService.java

@@ -60,6 +60,7 @@
 import java.util.Optional;
 import java.util.Set;
 import java.util.Stack;
+import java.util.concurrent.ConcurrentHashMap;
 import java.util.stream.Collectors;
 
 import lombok.extern.slf4j.Slf4j;
@@ -79,7 +80,7 @@ public class SignedWitnessService {
 
     // The getSignedWitnessSet is called very often and is a bit expensive. We cache the result in that map but we
     // remove the cache entry if we get a matching SignedWitness added to the signedWitnessMap.
-    private final Map<P2PDataStorage.ByteArray, Set<SignedWitness>> getSignedWitnessSetCache = new HashMap<>();
+    private final Map<P2PDataStorage.ByteArray, Set<SignedWitness>> getSignedWitnessSetCache = new ConcurrentHashMap<>();
 
     private final FilterManager filterManager;
 

core/src/main/java/bisq/core/account/witness/AccountAgeWitnessService.java

@@ -73,6 +73,7 @@
 import java.util.Optional;
 import java.util.Random;
 import java.util.Set;
+import java.util.concurrent.ConcurrentHashMap;
 import java.util.concurrent.TimeUnit;
 import java.util.stream.Collectors;
 import java.util.stream.Stream;
@@ -143,7 +144,7 @@ public String getDisplayString() {
     // The accountAgeWitnessMap is very large (70k items) and access is a bit expensive. We usually only access less
     // than 100 items, those who have offers online. So we use a cache for a fast lookup and only if
     // not found there we use the accountAgeWitnessMap and put then the new item into our cache.
-    private final Map<P2PDataStorage.ByteArray, AccountAgeWitness> accountAgeWitnessCache = new HashMap<>();
+    private final Map<P2PDataStorage.ByteArray, AccountAgeWitness> accountAgeWitnessCache = new ConcurrentHashMap<>();
 
 
     ///////////////////////////////////////////////////////////////////////////////////////////