PaperMC/patches/server/0671-Fix-GameProfileCache-concurrency.patch

From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Spottedleaf <Spottedleaf@users.noreply.github.com>
Date: Sat, 11 Jul 2020 05:09:28 -0700
Subject: [PATCH] Fix GameProfileCache concurrency

Separate lookup and state access locks prevent lookups
from stalling simple state access/write calls

diff --git a/src/main/java/net/minecraft/server/players/GameProfileCache.java b/src/main/java/net/minecraft/server/players/GameProfileCache.java
index eac9658fa4cab7a651e10e4e18c679e040e4aed0..f4d903ed4342c3100c30deda291dfd6dd4e1ef40 100644
--- a/src/main/java/net/minecraft/server/players/GameProfileCache.java
+++ b/src/main/java/net/minecraft/server/players/GameProfileCache.java
@@ -60,6 +60,11 @@ public class GameProfileCache {
     @Nullable
     private Executor executor;
 
+    // Paper start
+    protected final java.util.concurrent.locks.ReentrantLock stateLock = new java.util.concurrent.locks.ReentrantLock();
+    protected final java.util.concurrent.locks.ReentrantLock lookupLock = new java.util.concurrent.locks.ReentrantLock();
+    // Paper end
+
     public GameProfileCache(GameProfileRepository profileRepository, File cacheFile) {
         this.profileRepository = profileRepository;
         this.file = cacheFile;
@@ -67,11 +72,13 @@ public class GameProfileCache {
     }
 
     private void safeAdd(GameProfileCache.GameProfileInfo entry) {
+        try { this.stateLock.lock(); // Paper - allow better concurrency
         GameProfile gameprofile = entry.getProfile();
 
         entry.setLastAccess(this.getNextOperation());
         this.profilesByName.put(gameprofile.getName().toLowerCase(Locale.ROOT), entry);
         this.profilesByUUID.put(gameprofile.getId(), entry);
+        } finally { this.stateLock.unlock(); } // Paper - allow better concurrency
     }
 
     private static Optional<GameProfile> lookupGameProfile(GameProfileRepository repository, String name) {
@@ -126,17 +133,20 @@ public class GameProfileCache {
 
     // Paper start
     public @Nullable GameProfile getProfileIfCached(String name) {
+        try { this.stateLock.lock(); // Paper - allow better concurrency
         GameProfileCache.GameProfileInfo entry = this.profilesByName.get(name.toLowerCase(Locale.ROOT));
         if (entry == null) {
             return null;
         }
         entry.setLastAccess(this.getNextOperation());
         return entry.getProfile();
+        } finally { this.stateLock.unlock(); } // Paper - allow better concurrency
     }
     // Paper end
 
     public Optional<GameProfile> get(String name) {
         String s1 = name.toLowerCase(Locale.ROOT);
+        boolean stateLocked = true; try { this.stateLock.lock(); // Paper - allow better concurrency
         GameProfileCache.GameProfileInfo usercache_usercacheentry = (GameProfileCache.GameProfileInfo) this.profilesByName.get(s1);
         boolean flag = false;
 
@@ -152,8 +162,12 @@ public class GameProfileCache {
         if (usercache_usercacheentry != null) {
             usercache_usercacheentry.setLastAccess(this.getNextOperation());
             optional = Optional.of(usercache_usercacheentry.getProfile());
+            stateLocked = false; this.stateLock.unlock(); // Paper - allow better concurrency
         } else {
+            stateLocked = false; this.stateLock.unlock(); // Paper - allow better concurrency
+            try { this.lookupLock.lock(); // Paper - allow better concurrency
             optional = GameProfileCache.lookupGameProfile(this.profileRepository, name); // Spigot - use correct case for offline players
+            } finally { this.lookupLock.unlock(); } // Paper - allow better concurrency
             if (optional.isPresent()) {
                 this.add((GameProfile) optional.get());
                 flag = false;
@@ -165,6 +179,7 @@ public class GameProfileCache {
         }
 
         return optional;
+        } finally { if (stateLocked) {  this.stateLock.unlock(); } } // Paper - allow better concurrency
     }
 
     public CompletableFuture<Optional<GameProfile>> getAsync(String username) {
@@ -189,6 +204,7 @@ public class GameProfileCache {
     }
 
     public Optional<GameProfile> get(UUID uuid) {
+        try { this.stateLock.lock(); // Paper - allow better concurrency
         GameProfileCache.GameProfileInfo usercache_usercacheentry = (GameProfileCache.GameProfileInfo) this.profilesByUUID.get(uuid);
 
         if (usercache_usercacheentry == null) {
@@ -197,6 +213,7 @@ public class GameProfileCache {
             usercache_usercacheentry.setLastAccess(this.getNextOperation());
             return Optional.of(usercache_usercacheentry.getProfile());
         }
+        } finally { this.stateLock.unlock(); } // Paper - allow better concurrency
     }
 
     public void setExecutor(Executor executor) {
@@ -277,7 +294,7 @@ public class GameProfileCache {
         JsonArray jsonarray = new JsonArray();
         DateFormat dateformat = GameProfileCache.createDateFormat();
 
-        this.getTopMRUProfiles(org.spigotmc.SpigotConfig.userCacheCap).forEach((usercache_usercacheentry) -> { // Spigot
+        this.listTopMRUProfiles(org.spigotmc.SpigotConfig.userCacheCap).forEach((usercache_usercacheentry) -> { // Spigot // Paper - allow better concurrency
             jsonarray.add(GameProfileCache.writeGameProfile(usercache_usercacheentry, dateformat));
         });
         String s = this.gson.toJson(jsonarray);
@@ -318,8 +335,19 @@ public class GameProfileCache {
     }
 
     private Stream<GameProfileCache.GameProfileInfo> getTopMRUProfiles(int limit) {
-        return ImmutableList.copyOf(this.profilesByUUID.values()).stream().sorted(Comparator.comparing(GameProfileCache.GameProfileInfo::getLastAccess).reversed()).limit((long) limit);
+        // Paper start - allow better concurrency
+        return this.listTopMRUProfiles(limit).stream();
+    }
+
+    private List<GameProfileCache.GameProfileInfo> listTopMRUProfiles(int limit) {
+        try {
+            this.stateLock.lock();
+            return this.profilesByUUID.values().stream().sorted(Comparator.comparing(GameProfileCache.GameProfileInfo::getLastAccess).reversed()).limit(limit).toList();
+        } finally {
+            this.stateLock.unlock();
+        }
     }
+    // Paper end
 
     private static JsonElement writeGameProfile(GameProfileCache.GameProfileInfo entry, DateFormat dateFormat) {
         JsonObject jsonobject = new JsonObject();