Add a basic API for retrieving spark statistics

22 files changed, 964 insertions, 19 deletions

diff --git a/settings.gradle b/settings.gradle
index 00a2eed..239b70a 100644
--- a/settings.gradle
+++ b/settings.gradle
@@ -11,6 +11,7 @@ pluginManagement {
 
 rootProject.name = 'spark'
 include (
+        'spark-api',
         'spark-common',
         'spark-bukkit',
         'spark-bungeecord',
diff --git a/spark-api/build.gradle b/spark-api/build.gradle
new file mode 100644
index 0000000..31458af
--- /dev/null
+++ b/spark-api/build.gradle
@@ -0,0 +1,32 @@
+plugins {
+    id 'maven-publish'
+}
+
+version = '0.1-SNAPSHOT'
+
+dependencies {
+    compileOnly 'org.checkerframework:checker-qual:3.8.0'
+    compileOnly 'org.jetbrains:annotations:20.1.0'
+}
+
+publishing {
+    //repositories {
+    //    maven {
+    //        url = 'https://oss.sonatype.org/content/repositories/snapshots'
+    //        credentials {
+    //            username = sonatypeUsername
+    //            password = sonatypePassword
+    //        }
+    //    }
+    //}
+    publications {
+        mavenJava(MavenPublication) {
+            from components.java
+            pom {
+                name = 'spark'
+                description = 'spark is a performance profiling plugin/mod for Minecraft clients, servers and proxies.'
+                url = 'https://spark.lucko.me/'
+            }
+        }
+    }
+}
diff --git a/spark-api/src/main/java/me/lucko/spark/api/Spark.java b/spark-api/src/main/java/me/lucko/spark/api/Spark.java
new file mode 100644
index 0000000..1f4ee64
--- /dev/null
+++ b/spark-api/src/main/java/me/lucko/spark/api/Spark.java
@@ -0,0 +1,79 @@
+/*
+ * This file is part of spark.
+ *
+ *  Copyright (c) lucko (Luck) <luck@lucko.me>
+ *  Copyright (c) contributors
+ *
+ *  This program is free software: you can redistribute it and/or modify
+ *  it under the terms of the GNU General Public License as published by
+ *  the Free Software Foundation, either version 3 of the License, or
+ *  (at your option) any later version.
+ *
+ *  This program is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *  GNU General Public License for more details.
+ *
+ *  You should have received a copy of the GNU General Public License
+ *  along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package me.lucko.spark.api;
+
+import me.lucko.spark.api.gc.GarbageCollector;
+import me.lucko.spark.api.statistic.misc.DoubleAverageInfo;
+import me.lucko.spark.api.statistic.types.DoubleStatistic;
+import me.lucko.spark.api.statistic.types.GenericStatistic;
+import me.lucko.spark.api.statistic.StatisticWindow;
+
+import org.checkerframework.checker.nullness.qual.NonNull;
+import org.checkerframework.checker.nullness.qual.Nullable;
+import org.jetbrains.annotations.Unmodifiable;
+
+import java.util.Map;
+
+/**
+ * The spark API.
+ */
+public interface Spark {
+
+    /**
+     * Gets the CPU usage statistic for the current process.
+     *
+     * @return the CPU process statistic
+     */
+    @NonNull DoubleStatistic<StatisticWindow.CpuUsage> cpuProcess();
+
+    /**
+     * Gets the CPU usage statistic for the overall system.
+     *
+     * @return the CPU system statistic
+     */
+    @NonNull DoubleStatistic<StatisticWindow.CpuUsage> cpuSystem();
+
+    /**
+     * Gets the ticks per second statistic.
+     *
+     * <p>Returns {@code null} if the statistic is not supported.</p>
+     *
+     * @return the ticks per second statistic
+     */
+    @Nullable DoubleStatistic<StatisticWindow.TicksPerSecond> tps();
+
+    /**
+     * Gets the milliseconds per tick statistic.
+     *
+     * <p>Returns {@code null} if the statistic is not supported.</p>
+     *
+     * @return the milliseconds per tick statistic
+     */
+    @Nullable GenericStatistic<DoubleAverageInfo, StatisticWindow.MillisPerTick> mspt();
+
+    /**
+     * Gets the garbage collector statistics.
+     *
+     * @return the garbage collector statistics
+     */
+    @NonNull @Unmodifiable Map<String, GarbageCollector> gc();
+
+}
diff --git a/spark-api/src/main/java/me/lucko/spark/api/SparkProvider.java b/spark-api/src/main/java/me/lucko/spark/api/SparkProvider.java
new file mode 100644
index 0000000..a93c27d
--- /dev/null
+++ b/spark-api/src/main/java/me/lucko/spark/api/SparkProvider.java
@@ -0,0 +1,53 @@
+/*
+ * This file is part of spark.
+ *
+ *  Copyright (c) lucko (Luck) <luck@lucko.me>
+ *  Copyright (c) contributors
+ *
+ *  This program is free software: you can redistribute it and/or modify
+ *  it under the terms of the GNU General Public License as published by
+ *  the Free Software Foundation, either version 3 of the License, or
+ *  (at your option) any later version.
+ *
+ *  This program is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *  GNU General Public License for more details.
+ *
+ *  You should have received a copy of the GNU General Public License
+ *  along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package me.lucko.spark.api;
+
+import org.checkerframework.checker.nullness.qual.NonNull;
+
+/**
+ * Singleton provider for {@link Spark}.
+ */
+public final class SparkProvider {
+
+    private static Spark instance;
+
+    /**
+     * Gets the singleton spark API instance.
+     *
+     * @return the spark API instance
+     */
+    public static @NonNull Spark get() {
+        Spark instance = SparkProvider.instance;
+        if (instance == null) {
+            throw new IllegalStateException("spark has not loaded yet!");
+        }
+        return instance;
+    }
+
+    static void set(Spark impl) {
+        SparkProvider.instance = impl;
+    }
+
+    private SparkProvider() {
+        throw new AssertionError();
+    }
+
+}
diff --git a/spark-api/src/main/java/me/lucko/spark/api/gc/GarbageCollector.java b/spark-api/src/main/java/me/lucko/spark/api/gc/GarbageCollector.java
new file mode 100644
index 0000000..b2c8801
--- /dev/null
+++ b/spark-api/src/main/java/me/lucko/spark/api/gc/GarbageCollector.java
@@ -0,0 +1,73 @@
+/*
+ * This file is part of spark.
+ *
+ *  Copyright (c) lucko (Luck) <luck@lucko.me>
+ *  Copyright (c) contributors
+ *
+ *  This program is free software: you can redistribute it and/or modify
+ *  it under the terms of the GNU General Public License as published by
+ *  the Free Software Foundation, either version 3 of the License, or
+ *  (at your option) any later version.
+ *
+ *  This program is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *  GNU General Public License for more details.
+ *
+ *  You should have received a copy of the GNU General Public License
+ *  along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package me.lucko.spark.api.gc;
+
+import org.checkerframework.checker.nullness.qual.NonNull;
+
+/**
+ * Statistics about a garbage collector.
+ *
+ * <p>All time durations are measured in milliseconds.</p>
+ */
+public interface GarbageCollector {
+
+    /**
+     * Gets the name of the garbage collector.
+     *
+     * @return the name
+     */
+    @NonNull String name();
+
+    /**
+     * Gets the total number of collections performed.
+     *
+     * @return the total number of collections
+     */
+    long totalCollections();
+
+    /**
+     * Gets the total amount of time spent performing collections.
+     *
+     * <p>Measured in milliseconds.</p>
+     *
+     * @return the total time spent collecting
+     */
+    long totalTime();
+
+    /**
+     * Gets the average amount of time spent performing each collection.
+     *
+     * <p>Measured in milliseconds.</p>
+     *
+     * @return the average collection time
+     */
+    double avgTime();
+
+    /**
+     * Gets the average frequency at which collections are performed.
+     *
+     * <p>Measured in milliseconds.</p>
+     *
+     * @return the average frequency of collections
+     */
+    long avgFrequency();
+
+}
diff --git a/spark-api/src/main/java/me/lucko/spark/api/statistic/Statistic.java b/spark-api/src/main/java/me/lucko/spark/api/statistic/Statistic.java
new file mode 100644
index 0000000..26af8e1
--- /dev/null
+++ b/spark-api/src/main/java/me/lucko/spark/api/statistic/Statistic.java
@@ -0,0 +1,46 @@
+/*
+ * This file is part of spark.
+ *
+ *  Copyright (c) lucko (Luck) <luck@lucko.me>
+ *  Copyright (c) contributors
+ *
+ *  This program is free software: you can redistribute it and/or modify
+ *  it under the terms of the GNU General Public License as published by
+ *  the Free Software Foundation, either version 3 of the License, or
+ *  (at your option) any later version.
+ *
+ *  This program is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *  GNU General Public License for more details.
+ *
+ *  You should have received a copy of the GNU General Public License
+ *  along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package me.lucko.spark.api.statistic;
+
+import org.checkerframework.checker.nullness.qual.NonNull;
+
+/**
+ * A statistic for which a rolling average in various windows is recorded.
+ *
+ * @param <W> the window type
+ */
+public interface Statistic<W extends Enum<W> & StatisticWindow> {
+
+    /**
+     * Gets the statistic name.
+     *
+     * @return the statistic name
+     */
+    @NonNull String name();
+
+    /**
+     * Gets the windows used for rolling averages.
+     *
+     * @return the windows
+     */
+    @NonNull W[] getWindows();
+
+}
diff --git a/spark-api/src/main/java/me/lucko/spark/api/statistic/StatisticWindow.java b/spark-api/src/main/java/me/lucko/spark/api/statistic/StatisticWindow.java
new file mode 100644
index 0000000..cfae9dd
--- /dev/null
+++ b/spark-api/src/main/java/me/lucko/spark/api/statistic/StatisticWindow.java
@@ -0,0 +1,104 @@
+/*
+ * This file is part of spark.
+ *
+ *  Copyright (c) lucko (Luck) <luck@lucko.me>
+ *  Copyright (c) contributors
+ *
+ *  This program is free software: you can redistribute it and/or modify
+ *  it under the terms of the GNU General Public License as published by
+ *  the Free Software Foundation, either version 3 of the License, or
+ *  (at your option) any later version.
+ *
+ *  This program is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *  GNU General Public License for more details.
+ *
+ *  You should have received a copy of the GNU General Public License
+ *  along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package me.lucko.spark.api.statistic;
+
+import org.checkerframework.checker.nullness.qual.NonNull;
+import org.jetbrains.annotations.NotNull;
+
+import java.time.Duration;
+
+/**
+ * A window in which a statistic is recorded as a rolling average.
+ */
+public interface StatisticWindow {
+
+    /**
+     * Gets the length of the window as a {@link Duration}.
+     *
+     * @return the length of the window
+     */
+    @NonNull Duration length();
+
+    /**
+     * The {@link StatisticWindow} used for CPU usage.
+     */
+    enum CpuUsage implements StatisticWindow {
+
+        SECONDS_10(Duration.ofSeconds(10)),
+        MINUTES_1(Duration.ofMinutes(1)),
+        MINUTES_15(Duration.ofMinutes(15));
+
+        private final Duration value;
+
+        CpuUsage(Duration value) {
+            this.value = value;
+        }
+
+        @Override
+        public @NotNull Duration length() {
+            return this.value;
+        }
+    }
+
+    /**
+     * The {@link StatisticWindow} used for TPS.
+     */
+    enum TicksPerSecond implements StatisticWindow {
+
+        SECONDS_5(Duration.ofSeconds(5)),
+        SECONDS_10(Duration.ofSeconds(10)),
+        MINUTES_1(Duration.ofMinutes(1)),
+        MINUTES_5(Duration.ofMinutes(5)),
+        MINUTES_15(Duration.ofMinutes(15));
+
+        private final Duration value;
+
+        TicksPerSecond(Duration value) {
+            this.value = value;
+        }
+
+        @Override
+        public @NotNull Duration length() {
+            return this.value;
+        }
+    }
+
+    /**
+     * The {@link StatisticWindow} used for MSPT.
+     */
+    enum MillisPerTick implements StatisticWindow {
+
+        SECONDS_10(Duration.ofSeconds(10)),
+        MINUTES_1(Duration.ofMinutes(1));
+
+        private final Duration value;
+
+        MillisPerTick(Duration value) {
+            this.value = value;
+        }
+
+        @Override
+        public @NotNull Duration length() {
+            return this.value;
+        }
+    }
+
+}
diff --git a/spark-api/src/main/java/me/lucko/spark/api/statistic/misc/DoubleAverageInfo.java b/spark-api/src/main/java/me/lucko/spark/api/statistic/misc/DoubleAverageInfo.java
new file mode 100644
index 0000000..0f882de
--- /dev/null
+++ b/spark-api/src/main/java/me/lucko/spark/api/statistic/misc/DoubleAverageInfo.java
@@ -0,0 +1,75 @@
+/*
+ * This file is part of spark.
+ *
+ *  Copyright (c) lucko (Luck) <luck@lucko.me>
+ *  Copyright (c) contributors
+ *
+ *  This program is free software: you can redistribute it and/or modify
+ *  it under the terms of the GNU General Public License as published by
+ *  the Free Software Foundation, either version 3 of the License, or
+ *  (at your option) any later version.
+ *
+ *  This program is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *  GNU General Public License for more details.
+ *
+ *  You should have received a copy of the GNU General Public License
+ *  along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package me.lucko.spark.api.statistic.misc;
+
+/**
+ * Statistics for a recorded double value.
+ */
+public interface DoubleAverageInfo {
+
+    /**
+     * Gets the mean value.
+     *
+     * @return the mean
+     */
+    double mean();
+
+    /**
+     * Gets the max value.
+     *
+     * @return the max
+     */
+    double max();
+
+    /**
+     * Gets the min value.
+     *
+     * @return the min
+     */
+    double min();
+
+    /**
+     * Gets the median value.
+     *
+     * @return the median
+     */
+    default double median() {
+        return percentile(0.50d);
+    }
+
+    /**
+     * Gets the 95th percentile value.
+     *
+     * @return the 95th percentile
+     */
+    default double percentile95th() {
+        return percentile(0.95d);
+    }
+
+    /**
+     * Gets the average value at a given percentile.
+     *
+     * @param percentile the percentile, as a double between 0 and 1.
+     * @return the average value at the given percentile
+     */
+    double percentile(double percentile);
+
+}
diff --git a/spark-api/src/main/java/me/lucko/spark/api/statistic/types/DoubleStatistic.java b/spark-api/src/main/java/me/lucko/spark/api/statistic/types/DoubleStatistic.java
new file mode 100644
index 0000000..ab26b7b
--- /dev/null
+++ b/spark-api/src/main/java/me/lucko/spark/api/statistic/types/DoubleStatistic.java
@@ -0,0 +1,50 @@
+/*
+ * This file is part of spark.
+ *
+ *  Copyright (c) lucko (Luck) <luck@lucko.me>
+ *  Copyright (c) contributors
+ *
+ *  This program is free software: you can redistribute it and/or modify
+ *  it under the terms of the GNU General Public License as published by
+ *  the Free Software Foundation, either version 3 of the License, or
+ *  (at your option) any later version.
+ *
+ *  This program is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *  GNU General Public License for more details.
+ *
+ *  You should have received a copy of the GNU General Public License
+ *  along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package me.lucko.spark.api.statistic.types;
+
+import me.lucko.spark.api.statistic.Statistic;
+import me.lucko.spark.api.statistic.StatisticWindow;
+
+import org.checkerframework.checker.nullness.qual.NonNull;
+
+/**
+ * A {@link Statistic} with a {@code double} value.
+ *
+ * @param <W> the window type
+ */
+public interface DoubleStatistic<W extends Enum<W> & StatisticWindow> extends Statistic<W> {
+
+    /**
+     * Polls the current value of the statistic in the given window.
+     *
+     * @param window the window
+     * @return the value
+     */
+    double poll(@NonNull W window);
+
+    /**
+     * Polls the current values of the statistic in all windows.
+     *
+     * @return the values
+     */
+    double[] poll();
+
+}
diff --git a/spark-api/src/main/java/me/lucko/spark/api/statistic/types/GenericStatistic.java b/spark-api/src/main/java/me/lucko/spark/api/statistic/types/GenericStatistic.java
new file mode 100644
index 0000000..2c27c05
--- /dev/null
+++ b/spark-api/src/main/java/me/lucko/spark/api/statistic/types/GenericStatistic.java
@@ -0,0 +1,51 @@
+/*
+ * This file is part of spark.
+ *
+ *  Copyright (c) lucko (Luck) <luck@lucko.me>
+ *  Copyright (c) contributors
+ *
+ *  This program is free software: you can redistribute it and/or modify
+ *  it under the terms of the GNU General Public License as published by
+ *  the Free Software Foundation, either version 3 of the License, or
+ *  (at your option) any later version.
+ *
+ *  This program is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *  GNU General Public License for more details.
+ *
+ *  You should have received a copy of the GNU General Public License
+ *  along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package me.lucko.spark.api.statistic.types;
+
+import me.lucko.spark.api.statistic.Statistic;
+import me.lucko.spark.api.statistic.StatisticWindow;
+
+import org.checkerframework.checker.nullness.qual.NonNull;
+
+/**
+ * A {@link Statistic} with a generic (non-primitive) type.
+ *
+ * @param <T> the generic value type
+ * @param <W> the window type
+ */
+public interface GenericStatistic<T, W extends Enum<W> & StatisticWindow> extends Statistic<W> {
+
+    /**
+     * Polls the current value of the statistic in the given window.
+     *
+     * @param window the window
+     * @return the value
+     */
+    T poll(@NonNull W window);
+
+    /**
+     * Polls the current values of the statistic in all windows.
+     *
+     * @return the values
+     */
+    T[] poll();
+
+}
diff --git a/spark-bukkit/src/main/java/me/lucko/spark/bukkit/BukkitSparkPlugin.java b/spark-bukkit/src/main/java/me/lucko/spark/bukkit/BukkitSparkPlugin.java
index 77fa64c..970c4b4 100644
--- a/spark-bukkit/src/main/java/me/lucko/spark/bukkit/BukkitSparkPlugin.java
+++ b/spark-bukkit/src/main/java/me/lucko/spark/bukkit/BukkitSparkPlugin.java
@@ -20,6 +20,7 @@
 
 package me.lucko.spark.bukkit;
 
+import me.lucko.spark.api.Spark;
 import me.lucko.spark.bukkit.placeholder.SparkMVdWPlaceholders;
 import me.lucko.spark.bukkit.placeholder.SparkPlaceholderApi;
 import me.lucko.spark.common.SparkPlatform;
@@ -35,6 +36,7 @@ import org.bukkit.ChatColor;
 import org.bukkit.command.Command;
 import org.bukkit.command.CommandExecutor;
 import org.bukkit.command.CommandSender;
+import org.bukkit.plugin.ServicePriority;
 import org.bukkit.plugin.java.JavaPlugin;
 
 import java.nio.file.Path;
@@ -162,6 +164,11 @@ public class BukkitSparkPlugin extends JavaPlugin implements SparkPlugin {
         return new BukkitPlatformInfo(getServer());
     }
 
+    @Override
+    public void registerApi(Spark api) {
+        getServer().getServicesManager().register(Spark.class, api, this, ServicePriority.Normal);
+    }
+
     private static boolean classExists(String className) {
         try {
             Class.forName(className);
diff --git a/spark-common/build.gradle b/spark-common/build.gradle
index ea4019d..8530a0e 100644
--- a/spark-common/build.gradle
+++ b/spark-common/build.gradle
@@ -3,6 +3,7 @@ plugins {
 }
 
 dependencies {
+    compile project(':spark-api')
     compile 'com.github.jvm-profiling-tools:async-profiler:v2.0'
     compile 'org.ow2.asm:asm:7.1'
     compile 'com.google.protobuf:protobuf-javalite:3.15.6'
@@ -25,6 +26,7 @@ dependencies {
     }
     compileOnly 'com.google.code.gson:gson:2.7'
     compileOnly 'com.google.guava:guava:19.0'
+    compileOnly 'org.checkerframework:checker-qual:3.8.0'
 }
 
 processResources {
diff --git a/spark-common/src/main/java/me/lucko/spark/common/SparkPlatform.java b/spark-common/src/main/java/me/lucko/spark/common/SparkPlatform.java
index c9aa030..099ad2d 100644
--- a/spark-common/src/main/java/me/lucko/spark/common/SparkPlatform.java
+++ b/spark-common/src/main/java/me/lucko/spark/common/SparkPlatform.java
@@ -24,6 +24,7 @@ import com.google.common.collect.ImmutableList;
 import com.google.common.collect.ImmutableMap;
 
 import me.lucko.spark.common.activitylog.ActivityLog;
+import me.lucko.spark.common.api.SparkApi;
 import me.lucko.spark.common.command.Arguments;
 import me.lucko.spark.common.command.Command;
 import me.lucko.spark.common.command.CommandModule;
@@ -89,6 +90,8 @@ public class SparkPlatform {
     private Map<String, GarbageCollectorStatistics> startupGcStatistics = ImmutableMap.of();
     private long serverNormalOperationStartTime;
 
+    private SparkApi api;
+
     public SparkPlatform(SparkPlugin plugin) {
         this.plugin = plugin;
 
@@ -131,6 +134,10 @@ public class SparkPlatform {
             this.startupGcStatistics = GarbageCollectorStatistics.pollStats();
             this.serverNormalOperationStartTime = System.currentTimeMillis();
         });
+
+        this.api = new SparkApi(this);
+        this.plugin.registerApi(this.api);
+        SparkApi.register(this.api);
     }
 
     public void disable() {
@@ -144,6 +151,8 @@ public class SparkPlatform {
         for (CommandModule module : this.commandModules) {
             module.close();
         }
+
+        SparkApi.unregister();
     }
 
     public SparkPlugin getPlugin() {
diff --git a/spark-common/src/main/java/me/lucko/spark/common/SparkPlugin.java b/spark-common/src/main/java/me/lucko/spark/common/SparkPlugin.java
index 171367e..216f23f 100644
--- a/spark-common/src/main/java/me/lucko/spark/common/SparkPlugin.java
+++ b/spark-common/src/main/java/me/lucko/spark/common/SparkPlugin.java
@@ -20,6 +20,7 @@
 
 package me.lucko.spark.common;
 
+import me.lucko.spark.api.Spark;
 import me.lucko.spark.common.command.sender.CommandSender;
 import me.lucko.spark.common.platform.PlatformInfo;
 import me.lucko.spark.common.sampler.ThreadDumper;
@@ -107,4 +108,8 @@ public interface SparkPlugin {
      */
     PlatformInfo getPlatformInfo();
 
+    default void registerApi(Spark api) {
+
+    }
+
 }
diff --git a/spark-common/src/main/java/me/lucko/spark/common/api/AbstractStatistic.java b/spark-common/src/main/java/me/lucko/spark/common/api/AbstractStatistic.java
new file mode 100644
index 0000000..49a6ccb
--- /dev/null
+++ b/spark-common/src/main/java/me/lucko/spark/common/api/AbstractStatistic.java
@@ -0,0 +1,85 @@
+/*
+ * This file is part of spark.
+ *
+ *  Copyright (c) lucko (Luck) <luck@lucko.me>
+ *  Copyright (c) contributors
+ *
+ *  This program is free software: you can redistribute it and/or modify
+ *  it under the terms of the GNU General Public License as published by
+ *  the Free Software Foundation, either version 3 of the License, or
+ *  (at your option) any later version.
+ *
+ *  This program is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *  GNU General Public License for more details.
+ *
+ *  You should have received a copy of the GNU General Public License
+ *  along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package me.lucko.spark.common.api;
+
+import me.lucko.spark.api.statistic.Statistic;
+import me.lucko.spark.api.statistic.StatisticWindow;
+import me.lucko.spark.api.statistic.types.DoubleStatistic;
+import me.lucko.spark.api.statistic.types.GenericStatistic;
+
+import org.checkerframework.checker.nullness.qual.NonNull;
+
+import java.lang.reflect.Array;
+import java.util.Arrays;
+
+public abstract class AbstractStatistic<W extends Enum<W> & StatisticWindow> implements Statistic<W> {
+    private final String name;
+    protected final W[] windows;
+
+    protected AbstractStatistic(String name, Class<W> enumClass) {
+        this.name = name;
+        this.windows = enumClass.getEnumConstants();
+    }
+
+    @Override
+    public @NonNull String name() {
+        return this.name;
+    }
+
+    @Override
+    public W[] getWindows() {
+        return Arrays.copyOf(this.windows, this.windows.length);
+    }
+
+    public static abstract class Double<W extends Enum<W> & StatisticWindow> extends AbstractStatistic<W> implements DoubleStatistic<W> {
+        public Double(String name, Class<W> enumClass) {
+            super(name, enumClass);
+        }
+
+        @Override
+        public double[] poll() {
+            double[] values = new double[this.windows.length];
+            for (int i = 0; i < values.length; i++) {
+                values[i] = poll(this.windows[i]);
+            }
+            return values;
+        }
+    }
+
+    public static abstract class Generic<T, W extends Enum<W> & StatisticWindow> extends AbstractStatistic<W> implements GenericStatistic<T, W> {
+        private final Class<T> typeClass;
+
+        public Generic(String name, Class<T> typeClass, Class<W> enumClass) {
+            super(name, enumClass);
+            this.typeClass = typeClass;
+        }
+
+        @SuppressWarnings("unchecked")
+        @Override
+        public T[] poll() {
+            T[] values = (T[]) Array.newInstance(this.typeClass, this.windows.length);
+            for (int i = 0; i < values.length; i++) {
+                values[i] = poll(this.windows[i]);
+            }
+            return values;
+        }
+    }
+}
diff --git a/spark-common/src/main/java/me/lucko/spark/common/api/GarbageCollectorInfo.java b/spark-common/src/main/java/me/lucko/spark/common/api/GarbageCollectorInfo.java
new file mode 100644
index 0000000..8d289aa
--- /dev/null
+++ b/spark-common/src/main/java/me/lucko/spark/common/api/GarbageCollectorInfo.java
@@ -0,0 +1,69 @@
+/*
+ * This file is part of spark.
+ *
+ *  Copyright (c) lucko (Luck) <luck@lucko.me>
+ *  Copyright (c) contributors
+ *