Rewrite chunk system (#8177)

Patch documentation to come

Issues with the old system that are fixed now:
- World generation does not scale with cpu cores effectively.
- Relies on the main thread for scheduling and maintaining chunk state, dropping chunk load/generate rates at lower tps.
- Unreliable prioritisation of chunk gen/load calls that block the main thread.
- Shutdown logic is utterly unreliable, as it has to wait for all chunks to unload - is it guaranteed that the chunk system is in a state on shutdown that it can reliably do this? Watchdog shutdown also typically failed due to thread checks, which is now resolved.
- Saving of data is not unified (i.e can save chunk data without saving entity data, poses problems for desync if shutdown is really abnormal.
- Entities are not loaded with chunks. This caused quite a bit of headache for Chunk#getEntities API, but now the new chunk system loads entities with chunks so that they are ready whenever the chunk loads in. Effectively brings the behavior back to 1.16 era, but still storing entities in their own separate regionfiles.

The above list is not complete. The patch documentation will complete it.

New chunk system hard relies on starlight and dataconverter, and most importantly the new concurrent utilities in ConcurrentUtil.

Some of the old async chunk i/o interface (i.e the old file io thread reroutes _some_ calls to the new file io thread) is kept for plugin compat reasons. It will be removed in the next major version of minecraft.

The old legacy chunk system patches have been moved to the removed folder in case we need them again.

1 files changed, 63 insertions, 0 deletions

diff --git a/patches/server/0409-Wait-for-Async-Tasks-during-shutdown.patch b/patches/server/0409-Wait-for-Async-Tasks-during-shutdown.patch
new file mode 100644
index 0000000000..ba50c6bb9e
--- /dev/null
+++ b/patches/server/0409-Wait-for-Async-Tasks-during-shutdown.patch
@@ -0,0 +1,63 @@
+From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
+From: Aikar <[email protected]>
+Date: Sun, 10 May 2020 22:16:17 -0400
+Subject: [PATCH] Wait for Async Tasks during shutdown
+
+Server.reload() had this logic to give time for tasks to shutdown,
+however shutdown did not...
+
+Adds a 5 second grace period for any async tasks to finish and warns
+if any are still running after that delay just as reload does.
+
+diff --git a/src/main/java/net/minecraft/server/MinecraftServer.java b/src/main/java/net/minecraft/server/MinecraftServer.java
+index 2fa1a4e453ac908848053ef80f6401764b0bb7f9..3c7154e85c4543a01a4e95b9f574f5d803a59e6c 100644
+--- a/src/main/java/net/minecraft/server/MinecraftServer.java
++++ b/src/main/java/net/minecraft/server/MinecraftServer.java
+@@ -921,6 +921,7 @@ public abstract class MinecraftServer extends ReentrantBlockableEventLoop<TickTa
+         // CraftBukkit start
+         if (this.server != null) {
+             this.server.disablePlugins();
++            this.server.waitForAsyncTasksShutdown(); // Paper
+         }
+         // CraftBukkit end
+         if (this.getConnection() != null) {
+diff --git a/src/main/java/org/bukkit/craftbukkit/CraftServer.java b/src/main/java/org/bukkit/craftbukkit/CraftServer.java
+index 547bb2aab1c31cbd2d571a995c1014726993b39f..ef6ca51679c818989f3ddd83f0bc7f37db6d6196 100644
+--- a/src/main/java/org/bukkit/craftbukkit/CraftServer.java
++++ b/src/main/java/org/bukkit/craftbukkit/CraftServer.java
+@@ -1011,6 +1011,35 @@ public final class CraftServer implements Server {
+         org.spigotmc.WatchdogThread.hasStarted = true; // Paper - Disable watchdog early timeout on reload
+     }
+ 
++    // Paper start
++    public void waitForAsyncTasksShutdown() {
++        int pollCount = 0;
++
++        // Wait for at most 5 seconds for plugins to close their threads
++        while (pollCount < 10*5 && getScheduler().getActiveWorkers().size() > 0) {
++            try {
++                Thread.sleep(100);
++            } catch (InterruptedException e) {}
++            pollCount++;
++        }
++
++        List<BukkitWorker> overdueWorkers = getScheduler().getActiveWorkers();
++        for (BukkitWorker worker : overdueWorkers) {
++            Plugin plugin = worker.getOwner();
++            String author = "<NoAuthorGiven>";
++            if (plugin.getDescription().getAuthors().size() > 0) {
++                author = plugin.getDescription().getAuthors().get(0);
++            }
++            getLogger().log(Level.SEVERE, String.format(
++                "Nag author: '%s' of '%s' about the following: %s",
++                author,
++                plugin.getDescription().getName(),
++                "This plugin is not properly shutting down its async tasks when it is being shut down. This task may throw errors during the final shutdown logs and might not complete before process dies."
++            ));
++        }
++    }
++    // Paper end
++
+     @Override
+     public void reloadData() {
+         ReloadCommand.reload(console);