Use ConcurrentHashMap in JsonList

This is specifically aimed at fixing #471

Using a ConcurrentHashMap because thread safety
The performance benefit of Map over ConcurrentMap is negligabe at best in this scenaio, as most operations will be get and not add or remove
Even without considering the use-case the benefits are still negligable

Original ideas for the system included an expiration policy and/or handler
The simpler solution was to use a computeIfPresent in the get method
This will simultaneously have an O(1) lookup time and automatically expire any values
Since the get method (nor other similar methods) don't seem to have a critical need to flush the map to disk at any of these points further processing is simply wasteful
Meaning the original function expired values unrelated to the current value without actually having any explicit need to

The h method was heavily modified to be much more efficient in its processing
Also instead of being called on every get, it's now called just before a save
This will eliminate stale values being flushed to disk

Modified isEmpty to use the isEmpty() method instead of the slightly confusing size() < 1
The point of this is readability, but does have a side-benefit of a small microptimization

paper-server/patches/sources/net/minecraft/server/players/PlayerList.java.patch

@@ -489,7 +489,7 @@
 +        } else if (!this.isWhiteListed(gameprofile, event)) { // Paper - ProfileWhitelistVerifyEvent
 +            //ichatmutablecomponent = Component.translatable("multiplayer.disconnect.not_whitelisted"); // Paper
 +            //event.disallow(PlayerLoginEvent.Result.KICK_WHITELIST, net.kyori.adventure.text.serializer.legacy.LegacyComponentSerializer.legacySection().deserialize(org.spigotmc.SpigotConfig.whitelistMessage)); // Spigot // Paper - Adventure - moved to isWhitelisted
-+        } else if (this.getIpBans().isBanned(socketaddress) && !this.getIpBans().get(socketaddress).hasExpired()) {
++        } else if (this.getIpBans().isBanned(socketaddress) && getIpBans().get(socketaddress) != null && !this.getIpBans().get(socketaddress).hasExpired()) { // Paper - fix NPE with temp ip bans
 +            IpBanListEntry ipbanentry = this.ipBans.get(socketaddress);
  
              ichatmutablecomponent = Component.translatable("multiplayer.disconnect.banned_ip.reason", ipbanentry.getReason());

paper-server/patches/sources/net/minecraft/server/players/StoredUserList.java.patch

@@ -1,15 +1,38 @@
 --- a/net/minecraft/server/players/StoredUserList.java
 +++ b/net/minecraft/server/players/StoredUserList.java
-@@ -54,7 +54,7 @@
+@@ -30,7 +30,7 @@
+     private static final Logger LOGGER = LogUtils.getLogger();
+     private static final Gson GSON = (new GsonBuilder()).setPrettyPrinting().create();
+     private final File file;
+-    private final Map<String, V> map = Maps.newHashMap();
++    private final Map<String, V> map = Maps.newConcurrentMap(); // Paper - Use ConcurrentHashMap in JsonList
+ 
+     public StoredUserList(File file) {
+         this.file = file;
+@@ -53,8 +53,11 @@
+ 
      @Nullable
      public V get(K key) {
-         this.removeExpired();
+-        this.removeExpired();
 -        return (StoredUserEntry) this.map.get(this.getKeyForUser(key));
-+        return (V) this.map.get(this.getKeyForUser(key)); // CraftBukkit - fix decompile error
++        // Paper start - Use ConcurrentHashMap in JsonList
++        return (V) this.map.computeIfPresent(this.getKeyForUser(key), (k, v) -> {
++            return v.hasExpired() ? null : v;
++        });
++        // Paper end - Use ConcurrentHashMap in JsonList
      }
  
      public void remove(K key) {
-@@ -85,6 +85,7 @@
+@@ -77,7 +80,7 @@
+     }
+ 
+     public boolean isEmpty() {
+-        return this.map.size() < 1;
++        return this.map.isEmpty(); // Paper - Use ConcurrentHashMap in JsonList
+     }
+ 
+     protected String getKeyForUser(K profile) {
+@@ -85,29 +88,12 @@
      }
  
      protected boolean contains(K k0) {
@@ -17,34 +40,42 @@
          return this.map.containsKey(this.getKeyForUser(k0));
      }
  
-@@ -93,7 +94,7 @@
-         Iterator iterator = this.map.values().iterator();
- 
-         while (iterator.hasNext()) {
+     private void removeExpired() {
+-        List<K> list = Lists.newArrayList();
+-        Iterator iterator = this.map.values().iterator();
+-
+-        while (iterator.hasNext()) {
 -            V v0 = (StoredUserEntry) iterator.next();
-+            V v0 = (V) iterator.next(); // CraftBukkit - decompile error
- 
-             if (v0.hasExpired()) {
-                 list.add(v0.getUser());
-@@ -103,7 +104,7 @@
-         iterator = list.iterator();
- 
-         while (iterator.hasNext()) {
+-
+-            if (v0.hasExpired()) {
+-                list.add(v0.getUser());
+-            }
+-        }
+-
+-        iterator = list.iterator();
+-
+-        while (iterator.hasNext()) {
 -            K k0 = iterator.next();
-+            K k0 = (K) iterator.next(); // CraftBukkit - decompile error
+-
+-            this.map.remove(this.getKeyForUser(k0));
+-        }
+-
++        this.map.values().removeIf(StoredUserEntry::hasExpired); // Paper - Use ConcurrentHashMap in JsonList
+     }
  
-             this.map.remove(this.getKeyForUser(k0));
-         }
-@@ -118,7 +119,7 @@
+     protected abstract StoredUserEntry<K> createEntry(JsonObject json);
+@@ -117,8 +103,9 @@
+     }
  
      public void save() throws IOException {
++        this.removeExpired(); // Paper - remove expired values before saving
          JsonArray jsonarray = new JsonArray();
 -        Stream stream = this.map.values().stream().map((jsonlistentry) -> {
 +        Stream<JsonObject> stream = this.map.values().stream().map((jsonlistentry) -> { // CraftBukkit - decompile error
              JsonObject jsonobject = new JsonObject();
  
              Objects.requireNonNull(jsonlistentry);
-@@ -171,9 +172,17 @@
+@@ -171,9 +158,17 @@
                          StoredUserEntry<K> jsonlistentry = this.createEntry(jsonobject);
  
                          if (jsonlistentry.getUser() != null) {