Flush regionfiles on save configuration option

The windows file system does not write metadata unless
the FileChannel is explicitly flushed with metaData=true.

Note: Setting SYNC (not DSYNC) on the FileChannel does not appear
to write the metadata.

Specifically, we are interested in writing the last modified
timestamp so that fs watchers can detect when RegionFiles are
modified.

paper-server/patches/features/0030-Flush-regionfiles-on-save-configuration-option.patch

@@ -0,0 +1,34 @@
+From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
+From: Spottedleaf <[email protected]>
+Date: Mon, 20 Jan 2025 13:30:34 -0800
+Subject: [PATCH] Flush regionfiles on save configuration option
+
+The windows file system does not write metadata unless
+the FileChannel is explicitly flushed with metaData=true.
+
+Note: Setting SYNC (not DSYNC) on the FileChannel does not appear
+to write the metadata.
+
+Specifically, we are interested in writing the last modified
+timestamp so that fs watchers can detect when RegionFiles are
+modified.
+
+diff --git a/ca/spottedleaf/moonrise/patches/chunk_system/io/MoonriseRegionFileIO.java b/ca/spottedleaf/moonrise/patches/chunk_system/io/MoonriseRegionFileIO.java
+index 1acea58838f057ab87efd103cbecb6f5aeaef393..98fbc5c8044bd945d64569f13412a6e7e49a4e7f 100644
+--- a/ca/spottedleaf/moonrise/patches/chunk_system/io/MoonriseRegionFileIO.java
++++ b/ca/spottedleaf/moonrise/patches/chunk_system/io/MoonriseRegionFileIO.java
+@@ -1258,6 +1258,14 @@ public final class MoonriseRegionFileIO {
+
+             try {
+                 this.regionDataController.finishWrite(this.chunkX, this.chunkZ, writeData);
++                // Paper start - flush regionfiles on save
++                if (this.world.paperConfig().chunks.flushRegionsOnSave) {
++                    final RegionFile regionFile = this.regionDataController.getCache().moonrise$getRegionFileIfLoaded(this.chunkX, this.chunkZ);
++                    if (regionFile != null) {
++                        regionFile.flush();
++                    } // else: evicted from cache, which should have called flush
++                }
++                // Paper end - flush regionfiles on save
+             } catch (final Throwable thr) {
+                 failedWrite = thr instanceof IOException;
+                 LOGGER.error("Failed to write chunk data for task: " + this.toString(), thr);