Restore incremental player saving

This patch was dropped in 1.14 . I couldn't find it in removed so I got it from 1.13
Tested with 30-40 players and works fine with default settings.
Closes https://github.com/PaperMC/Paper/issues/4070

Spigot-Server-Patches/0551-Incremental-player-saving.patch

@@ -0,0 +1,95 @@
+From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
+From: Aikar <aikar@aikar.co>
+Date: Sun, 9 Aug 2020 08:59:25 +0300
+Subject: [PATCH] Incremental player saving
+
+
+diff --git a/src/main/java/com/destroystokyo/paper/PaperConfig.java b/src/main/java/com/destroystokyo/paper/PaperConfig.java
+index 56e4359ba32339e1bef58061585ff3e12e4215f3..60f03502a7fd622d2de3b2da9fe8014b289f3d31 100644
+--- a/src/main/java/com/destroystokyo/paper/PaperConfig.java
++++ b/src/main/java/com/destroystokyo/paper/PaperConfig.java
+@@ -435,4 +435,15 @@ public class PaperConfig {
+         allowPistonDuplication = getBoolean("settings.unsupported-settings.allow-piston-duplication", config.getBoolean("settings.unsupported-settings.allow-tnt-duplication", false));
+         set("settings.unsupported-settings.allow-tnt-duplication", null);
+     }
++
++    public static int playerAutoSaveRate = -1;
++    public static int maxPlayerAutoSavePerTick = 10;
++    private static void playerAutoSaveRate() {
++        playerAutoSaveRate = getInt("settings.player-auto-save-rate", -1);
++        maxPlayerAutoSavePerTick = getInt("settings.max-player-auto-save-per-tick", -1);
++        if (maxPlayerAutoSavePerTick == -1) { // -1 Automatic / "Recommended"
++            // 10 should be safe for everyone unless you mass spamming player auto save
++            maxPlayerAutoSavePerTick = (playerAutoSaveRate == -1 || playerAutoSaveRate > 100) ? 10 : 20;
++        }
++    }
+ }
+diff --git a/src/main/java/net/minecraft/server/EntityPlayer.java b/src/main/java/net/minecraft/server/EntityPlayer.java
+index e5a81f831813209d224ffedbc03f6d8243721a25..c72cfd2bdfbe4536f6799fc4dff195c1f66d4c94 100644
+--- a/src/main/java/net/minecraft/server/EntityPlayer.java
++++ b/src/main/java/net/minecraft/server/EntityPlayer.java
+@@ -42,6 +42,7 @@ import org.bukkit.inventory.MainHand;
+ public class EntityPlayer extends EntityHuman implements ICrafting {
+ 
+     private static final Logger LOGGER = LogManager.getLogger();
++    public long lastSave = MinecraftServer.currentTick; // Paper
+     public PlayerConnection playerConnection;
+     public NetworkManager networkManager; // Paper
+     public final MinecraftServer server;
+diff --git a/src/main/java/net/minecraft/server/MinecraftServer.java b/src/main/java/net/minecraft/server/MinecraftServer.java
+index 3130c68e7318a41e763575b245ee1b5298c92a16..0defaec8a8a25b1a0172f211d599d07264977cfa 100644
+--- a/src/main/java/net/minecraft/server/MinecraftServer.java
++++ b/src/main/java/net/minecraft/server/MinecraftServer.java
+@@ -1228,9 +1228,15 @@ public abstract class MinecraftServer extends IAsyncTaskHandlerReentrant<TickTas
+         //if (autosavePeriod > 0 && this.ticks % autosavePeriod == 0) { // CraftBukkit // Paper - move down
+             //MinecraftServer.LOGGER.debug("Autosave started"); // Paper
+             serverAutoSave = (autosavePeriod > 0 && this.ticks % autosavePeriod == 0); // Paper
++            // Paper start
++            int playerSaveInterval = com.destroystokyo.paper.PaperConfig.playerAutoSaveRate;
++            if (playerSaveInterval < 0) {
++                playerSaveInterval = autosavePeriod;
++            }
++            // Paper end
+             this.methodProfiler.enter("save");
+-            if (autosavePeriod > 0 && this.ticks % autosavePeriod == 0) { // Paper
+-            this.playerList.savePlayers();
++            if (playerSaveInterval > 0) { // Paper
++            this.playerList.savePlayers(playerSaveInterval); // Paper
+             }// Paper
+             // Paper start
+             for (WorldServer world : getWorlds()) {
+diff --git a/src/main/java/net/minecraft/server/PlayerList.java b/src/main/java/net/minecraft/server/PlayerList.java
+index 9382e8f79e8edec8885c629a36e230fbec50e1fb..38d83bb3183c6b8d7708e27b7427a757e3d26b0f 100644
+--- a/src/main/java/net/minecraft/server/PlayerList.java
++++ b/src/main/java/net/minecraft/server/PlayerList.java
+@@ -482,6 +482,7 @@ public abstract class PlayerList {
+     protected void savePlayerFile(EntityPlayer entityplayer) {
+         if (!entityplayer.getBukkitEntity().isPersistent()) return; // CraftBukkit
+         if (!entityplayer.didPlayerJoinEvent) return; // Paper - If we never fired PJE, we disconnected during login. Data has not changed, and additionally, our saved vehicle is not loaded! If we save now, we will lose our vehicle (CraftBukkit bug)
++        entityplayer.lastSave = MinecraftServer.currentTick; // Paper
+         this.playerFileData.save(entityplayer);
+         ServerStatisticManager serverstatisticmanager = (ServerStatisticManager) entityplayer.getStatisticManager(); // CraftBukkit
+ 
+@@ -1127,10 +1128,21 @@ public abstract class PlayerList {
+     }
+ 
+     public void savePlayers() {
++        // Paper start - incremental player saving
++        savePlayers(null);
++    }
++    public void savePlayers(Integer interval) {
+         MCUtil.ensureMain("Save Players" , () -> { // Paper - Ensure main
+         MinecraftTimings.savePlayers.startTiming(); // Paper
++        int numSaved = 0;
++        long now = MinecraftServer.currentTick;
+         for (int i = 0; i < this.players.size(); ++i) {
+-            this.savePlayerFile((EntityPlayer) this.players.get(i));
++            EntityPlayer entityplayer = this.players.get(i);
++            if (interval == null || now - entityplayer.lastSave >= interval) {
++                this.savePlayerFile(entityplayer);
++                if (interval != null && ++numSaved <= com.destroystokyo.paper.PaperConfig.maxPlayerAutoSavePerTick) { break; }
++            }
++            // Paper end
+         }
+         MinecraftTimings.savePlayers.stopTiming(); // Paper
+         return null; }); // Paper - ensure main