Run extension pre/post/init at sensible times.

src/main/java/net/minestom/server/MinecraftServer.java

@@ -617,12 +617,17 @@ public final class MinecraftServer {
         Check.stateCondition(!initialized, "#start can only be called after #init");
         Check.stateCondition(started, "The server is already started");
 
+        extensionManager.start();
+        extensionManager.gotoPreInit();
+
         MinecraftServer.started = true;
 
         LOGGER.info("Starting Minestom server.");
 
         updateManager.start();
 
+        extensionManager.gotoInit();
+
         // Init server
         try {
             server.init(new InetSocketAddress(address, port));
@@ -630,24 +635,11 @@ public final class MinecraftServer {
             e.printStackTrace();
         }
 
-        if (extensionManager.shouldLoadOnStartup()) {
-            final long loadStartTime = System.nanoTime();
-            // Load extensions
-            extensionManager.loadExtensions();
-            // Init extensions
-            extensionManager.getExtensions().forEach(Extension::preInitialize);
-            extensionManager.getExtensions().forEach(Extension::initialize);
-            extensionManager.getExtensions().forEach(Extension::postInitialize);
-
-            final double loadTime = MathUtils.round((System.nanoTime() - loadStartTime) / 1_000_000D, 2);
-            LOGGER.info("Extensions loaded in {}ms", loadTime);
-        } else {
-            LOGGER.warn("Extension loadOnStartup option is set to false, extensions are therefore neither loaded or initialized.");
-        }
-
         // Start server
         server.start();
 
+        extensionManager.gotoPostInit();
+
         LOGGER.info("Minestom server started successfully.");
 
         if (terminalEnabled) {

src/main/java/net/minestom/server/extensions/ExtensionManager.java

@@ -9,6 +9,7 @@ import net.minestom.server.event.Event;
 import net.minestom.server.event.EventNode;
 import net.minestom.server.ping.ResponseDataConsumer;
 import net.minestom.server.utils.validate.Check;
+import org.jetbrains.annotations.ApiStatus;
 import org.jetbrains.annotations.NotNull;
 import org.jetbrains.annotations.Nullable;
 import org.slf4j.Logger;
@@ -40,10 +41,7 @@ public class ExtensionManager {
     private final File extensionFolder = new File("extensions");
     private final File dependenciesFolder = new File(extensionFolder, ".libs");
     private Path extensionDataRoot = extensionFolder.toPath();
-    private boolean loaded;
+    private int state = 0; // -1=do not start, 0=not started, 1=started, 2=preinit, 3=init, 4=postinit
-
-    // Option
-    private boolean loadOnStartup = true;
 
     public ExtensionManager() {
     }
@@ -56,7 +54,7 @@ public class ExtensionManager {
      * @return true if extensions are loaded in {@link net.minestom.server.MinecraftServer#start(String, int, ResponseDataConsumer)}
      */
     public boolean shouldLoadOnStartup() {
-        return loadOnStartup;
+        return state != -1;
     }
 
     /**
@@ -67,7 +65,8 @@ public class ExtensionManager {
      * @param loadOnStartup true to load extensions on startup, false to do nothing
      */
     public void setLoadOnStartup(boolean loadOnStartup) {
-        this.loadOnStartup = loadOnStartup;
+        Check.stateCondition(state < 1, "Extensions have already been initialized");
+        this.state = loadOnStartup ? 0 : -1;
     }
 
     @NotNull
@@ -97,6 +96,45 @@ public class ExtensionManager {
         return extensions.containsKey(name);
     }
 
+    //
+    // Init phases
+    //
+
+    @ApiStatus.Internal
+    public void start() {
+        if (state == -1) {
+            LOGGER.warn("Extension loadOnStartup option is set to false, extensions are therefore neither loaded or initialized.");
+            return;
+        }
+        Check.stateCondition(state != 0, "ExtensionManager has already been started");
+        loadExtensions();
+        state = 1;
+    }
+
+    @ApiStatus.Internal
+    public void gotoPreInit() {
+        if (state == -1) return;
+        Check.stateCondition(state != 1, "Extensions have already done pre initialization");
+        extensions.values().forEach(Extension::preInitialize);
+        state = 2;
+    }
+
+    @ApiStatus.Internal
+    public void gotoInit() {
+        if (state == -1) return;
+        Check.stateCondition(state != 2, "Extensions have already done initialization");
+        extensions.values().forEach(Extension::initialize);
+        state = 3;
+    }
+
+    @ApiStatus.Internal
+    public void gotoPostInit() {
+        if (state == -1) return;
+        Check.stateCondition(state != 3, "Extensions have already done post initialization");
+        extensions.values().forEach(Extension::postInitialize);
+        state = 4;
+    }
+
     //
     // Loading
     //
@@ -143,10 +181,7 @@ public class ExtensionManager {
      * <p>
      * And finally make a scheduler to clean observers per extension.
      */
-    public void loadExtensions() {
+    private void loadExtensions() {
-        Check.stateCondition(loaded, "Extensions are already loaded!");
-        this.loaded = true;
-
         // Initialize folders
         {
             // Make extensions folder if necessary

src/test/java/testextension/TestExtension.java

@@ -1,8 +1,17 @@
 package testextension;
 
+import net.minestom.server.MinecraftServer;
 import net.minestom.server.extensions.Extension;
 
 public class TestExtension extends Extension {
+
+    @Override
+    public void preInitialize() {
+        System.out.println("During preinit");
+        MinecraftServer.setTerminalEnabled(false);
+        System.out.println("Mwahaha i disabled the terminal");
+    }
+
     @Override
     public void initialize() {
         System.out.println("Hello from extension!");