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Optimize Region File Cache

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CraftBukkit added synchronization to read and write methods. This adds
much more contention on this object for accessing region files, as
the entire read and write of NBT data is now a blocking operation.

This causes issues when something then simply needs to check if a chunk exists
on the main thread, causing a block...

However, this synchronization was unnecessary, because there is already
enough synchronization done to keep things safe

1) Obtaining a Region File: Those methods are still static synchronized.
   Meaning we can safely obtain a Region File concurrently.

2) RegionFile data access: Methods reading and manipulating data from
   a region file are also marked synchronized, ensuring that no 2 processes
   are reading or writing data at the same time.

3) Checking a region file for chunkExists: getOffset is also synchronized
   ensuring that even if a chunk is currently being written, it will be safe.

By removing these synchronizations, we reduce the locking to only
when data is being write or read.

GZIP compression and NBT Buffer creation will no longer be part of the
synchronized context, reducing lock times.

Ultimately: This brings us back to Vanilla, which has had no indication of region file loss.

Closes #1260
This commit is contained in:
Aikar 2018-07-23 23:50:09 -04:00
parent f51ad46686
commit 84d229cd29
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@ -0,0 +1,67 @@
From e979cf5f12f51ca8cea8931026b091f21cc62eb9 Mon Sep 17 00:00:00 2001
From: Aikar <aikar@aikar.co>
Date: Mon, 23 Jul 2018 23:40:04 -0400
Subject: [PATCH] Optimize Region File Cache
CraftBukkit added synchronization to read and write methods. This adds
much more contention on this object for accessing region files, as
the entire read and write of NBT data is now a blocking operation.
This causes issues when something then simply needs to check if a chunk exists
on the main thread, causing a block...
However, this synchronization was unnecessary, because there is already
enough synchronization done to keep things safe
1) Obtaining a Region File: Those methods are still static synchronized.
Meaning we can safely obtain a Region File concurrently.
2) RegionFile data access: Methods reading and manipulating data from
a region file are also marked synchronized, ensuring that no 2 processes
are reading or writing data at the same time.
3) Checking a region file for chunkExists: getOffset is also synchronized
ensuring that even if a chunk is currently being written, it will be safe.
By removing these synchronizations, we reduce the locking to only
when data is being write or read.
GZIP compression and NBT Buffer creation will no longer be part of the
synchronized context, reducing lock times.
Ultimately: This brings us back to Vanilla, which has had no indication of region file loss.
diff --git a/src/main/java/net/minecraft/server/RegionFileCache.java b/src/main/java/net/minecraft/server/RegionFileCache.java
index 3b8d01ea1..609d6c355 100644
--- a/src/main/java/net/minecraft/server/RegionFileCache.java
+++ b/src/main/java/net/minecraft/server/RegionFileCache.java
@@ -97,7 +97,7 @@ public class RegionFileCache {
@Nullable
// CraftBukkit start - call sites hoisted for synchronization
- public static synchronized NBTTagCompound read(File file, int i, int j) throws IOException {
+ public static NBTTagCompound read(File file, int i, int j) throws IOException { // Paper - remove synchronization
RegionFile regionfile = a(file, i, j);
DataInputStream datainputstream = regionfile.a(i & 31, j & 31);
@@ -110,7 +110,7 @@ public class RegionFileCache {
}
@Nullable
- public static synchronized void write(File file, int i, int j, NBTTagCompound nbttagcompound) throws IOException {
+ public static void write(File file, int i, int j, NBTTagCompound nbttagcompound) throws IOException { // Paper - remove synchronization
RegionFile regionfile = a(file, i, j);
DataOutputStream dataoutputstream = regionfile.c(i & 31, j & 31);
@@ -119,7 +119,7 @@ public class RegionFileCache {
}
// CraftBukkit end
- public static synchronized boolean chunkExists(File file, int i, int j) {
+ public static boolean chunkExists(File file, int i, int j) { // Paper - remove synchronization
RegionFile regionfile = b(file, i, j);
return regionfile != null ? regionfile.d(i & 31, j & 31) : false;
--
2.18.0