added async file IO

src/async_runtime/io/SelectorThread.java

@@ -0,0 +1,57 @@
+package async_runtime.io;
+
+import java.io.IOException;
+import java.nio.channels.*;
+import java.util.ArrayDeque;
+
+public abstract class SelectorThread<T extends SelectableChannel, A> extends Thread{
+
+    private final Selector selector;
+
+    private record  ToRegister<T, A>(T sc, int ops, A waker){}
+    private final ArrayDeque<ToRegister<T, A>> to_register = new ArrayDeque<>();
+
+
+    public SelectorThread(String name) throws IOException {
+        selector = Selector.open();
+        this.setName(name + " Polling Thread");
+        this.setDaemon(true);
+        this.start();
+    }
+
+    public abstract void handle(SelectionKey key, T t, A a) throws IOException;
+
+    public void register(T sc, int ops, A waker){
+        synchronized (to_register){
+            to_register.add(new ToRegister<>(sc, ops, waker));
+        }
+        selector.wakeup();
+    }
+
+    @SuppressWarnings("unchecked")
+    @Override
+    public void run() {
+        while(!Thread.currentThread().isInterrupted()){
+            try{
+                synchronized (to_register){
+                    while(!to_register.isEmpty()){
+                        var to = to_register.poll();
+                        to.sc.register(selector, to.ops, to.waker);
+                    }
+                }
+
+                selector.select();
+                var keys = selector.selectedKeys().iterator();
+
+                while (keys.hasNext()) {
+                    SelectionKey key = keys.next();
+                    keys.remove();
+
+                    handle(key, (T)key.channel(), (A)key.attachment());
+                }
+            }catch (Exception e){
+                e.printStackTrace();
+            }
+        }
+    }
+}