Paper/patches/server/0541-Synchronize-PalettedContainer-instead-of-ThreadingDe.patch
Spottedleaf 8c5b837e05 Rework async chunk api implementation
Firstly, the old methods all routed to the CompletableFuture method.
However, the CF method could not guarantee that if the caller
was off-main that the future would be "completed" on-main. Since
the callback methods used the CF one, this meant that the callback
methods did not guarantee that the callbacks were to be called on
the main thread.

Now, all methods route to getChunkAtAsync(x, z, gen, urgent, cb)
so that the methods with the callback are guaranteed to invoke
the callback on the main thread. The CF behavior remains unchanged;
it may still appear to complete on main if invoked off-main.

Secondly, remove the scheduleOnMain invocation in the async
chunk completion. This unnecessarily delays the callback
by 1 tick.

Thirdly, add getChunksAtAsync(minX, minZ, maxX, maxZ, ...) which
will load chunks within an area. This method is provided as a helper
as keeping all chunks loaded within an area can be complicated to
implement for plugins (due to the lacking ticket API), and is
already implemented internally anyways.

Fourthly, remove the ticket addition that occured with getChunkAt
and getChunkAtAsync. The ticket addition may delay the unloading
of the chunk unnecessarily. It also fixes a very rare timing bug
where the future/callback would be completed after the chunk
unloads.
2024-11-18 23:00:59 -08:00

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Diff

From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Aikar <aikar@aikar.co>
Date: Fri, 29 May 2020 20:29:02 -0400
Subject: [PATCH] Synchronize PalettedContainer instead of
ThreadingDetector/Semaphore
Mojang has flaws in their logic about chunks being concurrently
wrote to. So we constantly see crashes around multiple threads writing.
Additionally, java has optimized synchronization so well that its
in many times faster than trying to manage read write locks for low
contention situations.
And this is extremely a low contention situation.
diff --git a/src/main/java/net/minecraft/world/level/chunk/PalettedContainer.java b/src/main/java/net/minecraft/world/level/chunk/PalettedContainer.java
index 8c318c5f9eaaae1e961ff24247283c232fa84c20..112d1259dd37743076ff6c67ffd711d084ba8698 100644
--- a/src/main/java/net/minecraft/world/level/chunk/PalettedContainer.java
+++ b/src/main/java/net/minecraft/world/level/chunk/PalettedContainer.java
@@ -30,14 +30,14 @@ public class PalettedContainer<T> implements PaletteResize<T>, PalettedContainer
public final IdMap<T> registry;
private volatile PalettedContainer.Data<T> data;
private final PalettedContainer.Strategy strategy;
- private final ThreadingDetector threadingDetector = new ThreadingDetector("PalettedContainer");
+ // private final ThreadingDetector threadingDetector = new ThreadingDetector("PalettedContainer"); // Paper - unused
public void acquire() {
- this.threadingDetector.checkAndLock();
+ // this.threadingDetector.checkAndLock(); // Paper - disable this - use proper synchronization
}
public void release() {
- this.threadingDetector.checkAndUnlock();
+ // this.threadingDetector.checkAndUnlock(); // Paper - disable this
}
public static <T> Codec<PalettedContainer<T>> codecRW(IdMap<T> idList, Codec<T> entryCodec, PalettedContainer.Strategy paletteProvider, T defaultValue) {
@@ -110,7 +110,7 @@ public class PalettedContainer<T> implements PaletteResize<T>, PalettedContainer
}
@Override
- public int onResize(int newBits, T object) {
+ public synchronized int onResize(int newBits, T object) { // Paper - synchronize
PalettedContainer.Data<T> data = this.data;
PalettedContainer.Data<T> data2 = this.createOrReuseData(data, newBits);
data2.copyFrom(data.palette, data.storage);
@@ -135,7 +135,7 @@ public class PalettedContainer<T> implements PaletteResize<T>, PalettedContainer
return this.getAndSet(this.strategy.getIndex(x, y, z), value);
}
- private T getAndSet(int index, T value) {
+ private synchronized T getAndSet(int index, T value) { // Paper - synchronize
int i = this.data.palette.idFor(value);
int j = this.data.storage.getAndSet(index, i);
return this.data.palette.valueFor(j);
@@ -151,7 +151,7 @@ public class PalettedContainer<T> implements PaletteResize<T>, PalettedContainer
}
}
- private void set(int index, T value) {
+ private synchronized void set(int index, T value) { // Paper - synchronize
int i = this.data.palette.idFor(value);
this.data.storage.set(index, i);
}
@@ -174,7 +174,7 @@ public class PalettedContainer<T> implements PaletteResize<T>, PalettedContainer
intSet.forEach(id -> action.accept(palette.valueFor(id)));
}
- public void read(FriendlyByteBuf buf) {
+ public synchronized void read(FriendlyByteBuf buf) { // Paper - synchronize
this.acquire();
try {
@@ -189,7 +189,7 @@ public class PalettedContainer<T> implements PaletteResize<T>, PalettedContainer
}
@Override
- public void write(FriendlyByteBuf buf) {
+ public synchronized void write(FriendlyByteBuf buf) { // Paper - synchronize
this.acquire();
try {
@@ -237,7 +237,7 @@ public class PalettedContainer<T> implements PaletteResize<T>, PalettedContainer
}
@Override
- public PalettedContainerRO.PackedData<T> pack(IdMap<T> idList, PalettedContainer.Strategy paletteProvider) {
+ public synchronized PalettedContainerRO.PackedData<T> pack(IdMap<T> idList, PalettedContainer.Strategy paletteProvider) { // Paper - synchronize
this.acquire();
PalettedContainerRO.PackedData var12;