Mitigate excessive resource usage from Night Config

Author: embeddedt

forge/src/main/java/org/embeddedt/modernfix/forge/config/NightConfigWatchThrottler.java

@@ -0,0 +1,56 @@
+package org.embeddedt.modernfix.forge.config;
+
+import com.electronwill.nightconfig.core.file.FileWatcher;
+import com.google.common.collect.ForwardingCollection;
+import com.google.common.collect.ForwardingMap;
+import net.minecraftforge.fml.common.ObfuscationReflectionHelper;
+
+import java.util.Collection;
+import java.util.Iterator;
+import java.util.Map;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.locks.LockSupport;
+
+/**
+ * Throttle NightConfig's file watching. There are reports of this consuming excessive CPU time
+ * (<a href="https://github.com/TheElectronWill/night-config/pull/144">example</a>) and the spammed iterator calls
+ * end up being 10% of allocations when testing in a dev environment.
+ */
+public class NightConfigWatchThrottler {
+    private static final long DELAY = TimeUnit.MILLISECONDS.toNanos(1000);
+
+    @SuppressWarnings("rawtypes")
+    public static void throttle() {
+        Map watchedDirs = ObfuscationReflectionHelper.getPrivateValue(FileWatcher.class, FileWatcher.defaultInstance(), "watchedDirs");
+        ObfuscationReflectionHelper.setPrivateValue(FileWatcher.class, FileWatcher.defaultInstance(), new ForwardingMap() {
+            @Override
+            protected Map delegate() {
+                return watchedDirs;
+            }
+
+            private Collection cachedValues;
+
+            @Override
+            public Collection values() {
+                if(cachedValues == null) {
+                    Collection values = super.values();
+                    cachedValues = new ForwardingCollection() {
+                        @Override
+                        protected Collection delegate() {
+                            return values;
+                        }
+
+                        @Override
+                        public Iterator iterator() {
+                            // iterator() is called at the beginning of each iteration of the watch loop,
+                            // so it is a good spot to inject the delay.
+                            LockSupport.parkNanos(DELAY);
+                            return super.iterator();
+                        }
+                    };
+                }
+                return cachedValues;
+            }
+        }, "watchedDirs");
+    }
+}

forge/src/main/java/org/embeddedt/modernfix/platform/forge/ModernFixPlatformHooksImpl.java

@@ -31,6 +31,7 @@
 import org.embeddedt.modernfix.forge.classloading.FastAccessTransformerList;
 import org.embeddedt.modernfix.forge.classloading.ModernFixResourceFinder;
 import org.embeddedt.modernfix.forge.config.NightConfigFixer;
+import org.embeddedt.modernfix.forge.config.NightConfigWatchThrottler;
 import org.embeddedt.modernfix.forge.init.ModernFixForge;
 import org.embeddedt.modernfix.forge.packet.PacketHandler;
 import org.embeddedt.modernfix.forge.spark.SparkLaunchProfiler;
@@ -192,6 +193,7 @@ public void injectPlatformSpecificHacks() {
         }
 
         NightConfigFixer.monitorFileWatcher();
+        NightConfigWatchThrottler.throttle();
         MixinExtrasBootstrap.init();
     }