More accurately track tick times

I had a quick look at doing this per-world too, but I think doing this
in a way which is compatible with Forge and Fabric is tricky.

common/build.gradle.kts

@@ -12,6 +12,7 @@ minecraft {
 
 dependencies {
     compileOnlyApi(libs.jsr305)
+    compileOnly(libs.mixin)
 
     // Core libraries
     implementation(libs.bundles.prometheus)

common/src/main/java/cc/tweaked/prometheus/Constants.java

@@ -1,9 +1,13 @@
 package cc.tweaked.prometheus;
 
 public final class Constants {
-    public static final String NAMESPACE = "computercraft";
     public static final String MOD_ID = "ccprometheus";
 
+    /**
+     * The Prometheus namespace for the ComputerCraft-specific metrics.
+     */
+    public static final String COMPUTERCRAFT_NAMESPACE = "computercraft";
+
     private Constants() {
     }
 }

common/src/main/java/cc/tweaked/prometheus/collectors/ComputerCollector.java

@@ -5,21 +5,21 @@
 import dan200.computercraft.shared.computer.core.ServerContext;
 import io.prometheus.client.Gauge;
 
-import static cc.tweaked.prometheus.Constants.NAMESPACE;
+import static cc.tweaked.prometheus.Constants.COMPUTERCRAFT_NAMESPACE;
 
 /**
  * Counts the number of computers registered in the {@link ServerComputerRegistry}.
  */
 public class ComputerCollector {
     public static void register(MetricContext context) {
         var totalComputers = Gauge.build()
-            .namespace(NAMESPACE)
+            .namespace(COMPUTERCRAFT_NAMESPACE)
             .name("computers_total")
             .help("Total number of loaded computers")
             .register(context.registry());
 
         var onComputers = Gauge.build()
-            .namespace(NAMESPACE)
+            .namespace(COMPUTERCRAFT_NAMESPACE)
             .name("computers_on")
             .help("Total number of computers which are running")
             .register(context.registry());

common/src/main/java/cc/tweaked/prometheus/collectors/ComputerFieldCollector.java

@@ -14,7 +14,7 @@
 import java.util.Map;
 import java.util.Objects;
 
-import static cc.tweaked.prometheus.Constants.NAMESPACE;
+import static cc.tweaked.prometheus.Constants.COMPUTERCRAFT_NAMESPACE;
 
 /**
  * Reports the values for all {@link Metrics}s.
@@ -69,7 +69,7 @@ public void observe(ServerComputer computer, Metric.Event event, long value) {
     @SuppressWarnings("unchecked")
     private static <B extends SimpleCollector.Builder<?, ?>> B buildField(Metric field, B builder) {
         return (B) builder
-            .namespace(NAMESPACE)
+            .namespace(COMPUTERCRAFT_NAMESPACE)
             .name(field.name())
             .help(Objects.toString(new AggregatedMetric(field, Aggregate.NONE).displayName()))
             .labelNames("computer_id");

common/src/main/java/cc/tweaked/prometheus/collectors/ThreadGroupCollector.java

@@ -8,13 +8,13 @@
 import java.util.ArrayList;
 import java.util.List;
 
-import static cc.tweaked.prometheus.Constants.NAMESPACE;
+import static cc.tweaked.prometheus.Constants.COMPUTERCRAFT_NAMESPACE;
 
 /**
  * Counts the number of threads active in each of CC:T's thread groups.
  */
 public class ThreadGroupCollector extends Collector implements Collector.Describable {
-    private static final String FULL_NAME = NAMESPACE + "_thread_count";
+    private static final String FULL_NAME = COMPUTERCRAFT_NAMESPACE + "_thread_count";
     private static final String HELP = "Number of currently live threads";
     private static final List<String> LABEL_NAMES = List.of("group");
 

common/src/main/java/cc/tweaked/prometheus/collectors/VanillaCollector.java

@@ -24,6 +24,13 @@ public static void export(MetricContext context) {
             .help("The average tick time as defined by the MC server")
             .register(context.registry());
 
+        var dimensionTickTime = Histogram.build()
+            .namespace(NAMESPACE).name("tick_time").unit("s")
+            .buckets(0.005, 0.01, 0.025, 0.05, 0.10, 0.25, 0.5, 1.0)
+            .labelNames("dimension")
+            .help("The average tick time for each dimension")
+            .register(context.registry());
+
         var playerCount = Gauge.build()
             .namespace(NAMESPACE).name("players").unit("count")
             .help("The number of players in each dimension.")
@@ -49,10 +56,30 @@ public static void export(MetricContext context) {
             }
 
             totalPlayerCount.set(server.getPlayerCount());
+        });
 
-            // TODO: This doesn't include the time to run Forge/Fabric hooks! Not sure how to handle that in a generic way.
-            averageTickTime.set(server.getAverageTickTime() * 1e-3); // ms to s
-            tickTime.observe(server.tickTimes[server.getTickCount() % 100] * 1e-9); // ns to s.
+        ((MinecraftServerTimings) server).prometheus$setTimingObserver((time, averageTime) -> {
+            averageTickTime.set(averageTime * 1e-3); // ms to s
+            tickTime.observe(time * 1e-9); // ns to s.
         });
     }
+
+    public interface MinecraftServerTimings {
+        /**
+         * Set the object which monitors this server's timings.
+         *
+         * @param observer The timings observer.
+         */
+        void prometheus$setTimingObserver(TimingObserver observer);
+    }
+
+    public interface TimingObserver {
+        /**
+         * Called when a server finishes its tick.
+         *
+         * @param tickTime    The time taken for the last tick measured in nanoseconds.
+         * @param averageTime A smoothed version of tick times, measured in milliseconds.
+         */
+        void onServerTick(long tickTime, float averageTime);
+    }
 }

common/src/main/java/cc/tweaked/prometheus/mixin/MinecraftServerMixin.java

@@ -0,0 +1,49 @@
+package cc.tweaked.prometheus.mixin;
+
+import cc.tweaked.prometheus.collectors.VanillaCollector;
+import net.minecraft.Util;
+import net.minecraft.server.MinecraftServer;
+import org.spongepowered.asm.mixin.Mixin;
+import org.spongepowered.asm.mixin.Unique;
+import org.spongepowered.asm.mixin.injection.At;
+import org.spongepowered.asm.mixin.injection.Inject;
+import org.spongepowered.asm.mixin.injection.callback.CallbackInfo;
+
+/**
+ * {@link MinecraftServer#tickTimes}} (and the derived calculations) do not include main-thread tick tasks (those queued
+ * by {@link MinecraftServer#tell(Runnable)}) or from Fabric/Forge's tick events. We use our own mixins to more
+ * accurately capture this information.
+ */
+@Mixin(MinecraftServer.class)
+class MinecraftServerMixin implements VanillaCollector.MinecraftServerTimings {
+    @Unique
+    private VanillaCollector.TimingObserver observer;
+
+    @Unique
+    private float averageTickTime;
+
+    @Unique
+    private long tickStart;
+
+    @Inject(at = @At("HEAD"), method = "startMetricsRecordingTick")
+    private void beforeTick(CallbackInfo ci) {
+        tickStart = Util.getNanos();
+    }
+
+    @Inject(
+        method = "waitUntilNextTick",
+        at = @At(value = "INVOKE", target = "Lnet/minecraft/server/MinecraftServer;managedBlock(Ljava/util/function/BooleanSupplier;)V")
+    )
+    private void afterTick(CallbackInfo ci) {
+        // We want to inject here rather than endMetricsRecordingTick, as that also counts the sleep until the next tick.
+
+        long time = Util.getNanos() - tickStart;
+        averageTickTime = averageTickTime * 0.8F + (float) time / 1000000.0F * 0.19999999F;
+        if (observer != null) observer.onServerTick(time, averageTickTime);
+    }
+
+    @Override
+    public void prometheus$setTimingObserver(VanillaCollector.TimingObserver observer) {
+        this.observer = observer;
+    }
+}

common/src/main/resources/ccprometheus.mixins.json

@@ -0,0 +1,12 @@
+{
+    "required": true,
+    "package": "cc.tweaked.prometheus.mixin",
+    "minVersion": "0.8",
+    "compatibilityLevel": "JAVA_17",
+    "injectors": {
+        "defaultRequire": 1
+    },
+    "client": [
+        "MinecraftServerMixin"
+    ]
+}

fabric/src/main/resources/fabric.mod.json

@@ -26,5 +26,8 @@
     },
     "recommends": {
         "computercraft": "*"
-    }
+    },
+    "mixins": [
+        "ccprometheus.mixins.json"
+    ]
 }

forge/build.gradle.kts

@@ -3,6 +3,7 @@ plugins {
     alias(libs.plugins.shadow)
     alias(libs.plugins.forgeGradle)
     alias(libs.plugins.librarian)
+    alias(libs.plugins.mixinGradle)
     id("java-convention")
 }
 
@@ -59,6 +60,11 @@ tasks.jar {
     archiveClassifier.set("slim")
 }
 
+mixin {
+    add(sourceSets.main.get(), "ccprometheus.mixins.refmap.json")
+    config("ccprometheus.mixins.json")
+}
+
 reobf {
     create("shadowJar")
 }

gradle/libs.versions.toml

@@ -7,6 +7,7 @@ fabric-loader = "0.14.10"
 forge = "43.1.1"
 parchment = "2022.10.16"
 parchmentMc = "1.19.2"
+mixin = "0.8.5"
 
 # Normal dependencies
 jsr305 = "3.0.2"
@@ -23,6 +24,7 @@ forgeGradle = "5.1.+"
 librarian = "1.+"
 vanillaGradle = "0.2.1-SNAPSHOT"
 shadow = "7.1.2"
+mixinGradle = "0.7.+"
 
 [libraries]
 # Normal dependencies
@@ -40,18 +42,20 @@ prometheus-tracerOtel = { module = "io.prometheus:simpleclient_tracer_otel", ver
 prometheus-tracerOtelAgent = { module = "io.prometheus:simpleclient_tracer_otel_agent", version.ref = "prometheus" }
 
 # Minecraft mods
+cct-fabric = { module = "cc.tweaked:cc-tweaked-1.19.2-fabric", version.ref = "cct" }
+cct-forge = { module = "cc.tweaked:cc-tweaked-1.19.2-forge", version.ref = "cct" }
 fabric-api = { module = "net.fabricmc.fabric-api:fabric-api", version.ref = "fabric-api" }
 fabric-loader = { module = "net.fabricmc:fabric-loader", version.ref = "fabric-loader" }
 forgeConfig = { module = "net.minecraftforge:forgeconfigapiport-fabric", version.ref = "forgeConfig" }
-cct-forge = { module = "cc.tweaked:cc-tweaked-1.19.2-forge", version.ref = "cct" }
-cct-fabric = { module = "cc.tweaked:cc-tweaked-1.19.2-fabric", version.ref = "cct" }
+mixin = { module = "org.spongepowered:mixin", version.ref = "mixin" }
 
 [plugins]
-forgeGradle = { id = "net.minecraftforge.gradle", version.ref = "forgeGradle" }
 fabric-loom = { id = "fabric-loom", version.ref = "fabric-loom" }
+forgeGradle = { id = "net.minecraftforge.gradle", version.ref = "forgeGradle" }
 librarian = { id = "org.parchmentmc.librarian.forgegradle", version.ref = "librarian" }
-vanillaGradle = { id = "org.spongepowered.gradle.vanilla", version.ref = "vanillaGradle" }
+mixinGradle = { id = "org.spongepowered.mixin", version.ref = "mixinGradle" }
 shadow = { id = "com.github.johnrengelman.shadow", version.ref = "shadow" }
+vanillaGradle = { id = "org.spongepowered.gradle.vanilla", version.ref = "vanillaGradle" }
 
 [bundles]
 prometheus = [

gradle/wrapper/gradle-wrapper.properties

@@ -1,5 +1,5 @@
 distributionBase=GRADLE_USER_HOME
 distributionPath=wrapper/dists
-distributionUrl=https\://services.gradle.org/distributions/gradle-7.4.2-bin.zip
+distributionUrl=https\://services.gradle.org/distributions/gradle-7.5.1-bin.zip
 zipStoreBase=GRADLE_USER_HOME
 zipStorePath=wrapper/dists

settings.gradle.kts

@@ -34,6 +34,14 @@ pluginManagement {
             }
         }
     }
+
+    resolutionStrategy {
+        eachPlugin {
+            if (requested.id.id == "org.spongepowered.mixin") {
+                useModule("org.spongepowered:mixingradle:${requested.version}")
+            }
+        }
+    }
 }
 
 rootProject.name = "cc-prometheus"