Limit the total number of running threads

(Related #304)

core/src/main/java/com/github/games647/fastlogin/core/AsyncScheduler.java

@@ -0,0 +1,40 @@
+package com.github.games647.fastlogin.core;
+
+import java.util.concurrent.LinkedBlockingQueue;
+import java.util.concurrent.ThreadFactory;
+import java.util.concurrent.ThreadPoolExecutor;
+import java.util.concurrent.TimeUnit;
+
+/**
+ * This limits the number of threads that are used at maximum. Thread creation can be very heavy for the CPU and
+ * context switching between threads too. However we need many threads for blocking HTTP and database calls.
+ * Nevertheless this number can be further limited, because the number of actually working database threads
+ * is limited by the size of our database pool. The goal is to separate concerns into processing and blocking only
+ * threads.
+ */
+public class AsyncScheduler {
+
+    // 30 threads are still too many - the optimal solution is to separate into processing and blocking threads
+    // where processing threads could only be max number of cores while blocking threads could be minimized using
+    // non-blocking I/O and a single event executor
+    private final ThreadPoolExecutor executorService;
+
+    public AsyncScheduler(ThreadFactory threadFactory) {
+        executorService = new ThreadPoolExecutor(5, 30,
+                60L, TimeUnit.SECONDS,
+                new LinkedBlockingQueue<>(1024), threadFactory);
+    }
+
+    public void runAsync(Runnable task) {
+        executorService.execute(task);
+    }
+
+    public void shutdown() {
+        executorService.shutdown();
+        try {
+            executorService.awaitTermination(1, TimeUnit.MINUTES);
+        } catch (InterruptedException interruptEx) {
+            Thread.currentThread().interrupt();
+        }
+    }
+}

core/src/main/java/com/github/games647/fastlogin/core/AuthStorage.java

@@ -72,6 +72,9 @@ public class AuthStorage {
     }
 
     public void createTables() throws SQLException {
+        // choose surrogate PK(ID), because UUID can be null for offline players
+        // if UUID is always Premium UUID we would have to update offline player entries on insert
+        // name cannot be PK, because it can be changed for premium players
         String createDataStmt = "CREATE TABLE IF NOT EXISTS `" + PREMIUM_TABLE + "` ("
                 + "`UserID` INTEGER PRIMARY KEY AUTO_INCREMENT, "
                 + "`UUID` CHAR(36), "
@@ -87,7 +90,7 @@ public class AuthStorage {
             createDataStmt = createDataStmt.replace("AUTO_INCREMENT", "AUTOINCREMENT");
         }
 
-        //todo: add uuid index usage
+        //todo: add unique uuid index usage
         try (Connection con = dataSource.getConnection();
              Statement createStmt = con.createStatement()) {
             createStmt.executeUpdate(createDataStmt);

core/src/main/java/com/github/games647/fastlogin/core/shared/FastLoginCore.java

@@ -4,6 +4,7 @@ import com.github.games647.craftapi.resolver.MojangResolver;
 import com.github.games647.craftapi.resolver.http.RotatingProxySelector;
 import com.github.games647.fastlogin.core.AuthStorage;
 import com.github.games647.fastlogin.core.CommonUtil;
+import com.github.games647.fastlogin.core.AsyncScheduler;
 import com.github.games647.fastlogin.core.hooks.AuthPlugin;
 import com.github.games647.fastlogin.core.hooks.DefaultPasswordGenerator;
 import com.github.games647.fastlogin.core.hooks.PasswordGenerator;
@@ -51,6 +52,7 @@ public class FastLoginCore<P extends C, C, T extends PlatformPlugin<C>> {
     private final T plugin;
 
     private final MojangResolver resolver = new MojangResolver();
+    private final AsyncScheduler scheduler;
 
     private Configuration config;
     private AuthStorage storage;
@@ -59,6 +61,7 @@ public class FastLoginCore<P extends C, C, T extends PlatformPlugin<C>> {
 
     public FastLoginCore(T plugin) {
         this.plugin = plugin;
+        this.scheduler = new AsyncScheduler(plugin.getThreadFactory());
     }
 
     public void load() {
@@ -239,7 +242,14 @@ public class FastLoginCore<P extends C, C, T extends PlatformPlugin<C>> {
         }
     }
 
+    public AsyncScheduler getAsyncScheduler() {
+        return scheduler;
+    }
+
     public void close() {
+        plugin.getLog().info("Safely shutting down scheduler. This could take up to one minute.");
+        scheduler.shutdown();
+
         if (storage != null) {
             storage.close();
         }

core/src/main/java/com/github/games647/fastlogin/core/shared/PlatformPlugin.java

@@ -1,5 +1,7 @@
 package com.github.games647.fastlogin.core.shared;
 
+import com.google.common.util.concurrent.ThreadFactoryBuilder;
+
 import java.nio.file.Path;
 import java.util.concurrent.ThreadFactory;
 
@@ -22,6 +24,11 @@ public interface PlatformPlugin<C> {
     }
 
     default ThreadFactory getThreadFactory() {
-        return null;
+        return new ThreadFactoryBuilder()
+                .setNameFormat(getName() + " Pool Thread #%1$d")
+                // Hikari create daemons by default and we could daemon threads for our own scheduler too
+                // because we safely shutdown
+                .setDaemon(true)
+                .build();
     }
 }