optimizations, more comfortable PromiseFactory api and support virtual threaded executors

futur-api/src/main/java/dev/tommyjs/futur/joiner/ConcurrentResultArray.java

@@ -0,0 +1,32 @@
+package dev.tommyjs.futur.joiner;
+
+import org.jetbrains.annotations.NotNull;
+
+import java.util.Arrays;
+import java.util.List;
+import java.util.concurrent.atomic.AtomicReference;
+
+class ConcurrentResultArray<T> {
+
+    private final AtomicReference<T[]> ref;
+
+    public ConcurrentResultArray(int expectedSize) {
+        //noinspection unchecked
+        this.ref = new AtomicReference<>((T[]) new Object[expectedSize]);
+    }
+
+    public void set(int index, T element) {
+        ref.updateAndGet(array -> {
+            if (array.length <= index)
+                return Arrays.copyOf(array, index + 6);
+
+            array[index] = element;
+            return array;
+        });
+    }
+
+    public @NotNull List<T> toList() {
+        return Arrays.asList(ref.get());
+    }
+
+}