optimizations, more comfortable PromiseFactory api and support virtual threaded executors

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

@@ -0,0 +1,60 @@
+package dev.tommyjs.futur.joiner;
+
+import dev.tommyjs.futur.promise.Promise;
+import dev.tommyjs.futur.promise.PromiseCompletion;
+import dev.tommyjs.futur.promise.PromiseFactory;
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
+
+import java.util.*;
+import java.util.function.BiConsumer;
+
+public class MappedResultJoiner<K, V> extends PromiseJoiner<Map.Entry<K, Promise<V>>, K, V, Map<K, V>> {
+
+    private final @Nullable BiConsumer<K, Throwable> exceptionHandler;
+    private final @NotNull ConcurrentResultArray<Map.Entry<K, V>> results;
+
+    public MappedResultJoiner(
+        @NotNull PromiseFactory factory,
+        @NotNull Iterator<Map.Entry<K, Promise<V>>> promises,
+        @Nullable BiConsumer<K, Throwable> exceptionHandler,
+        int expectedSize, boolean link
+    ) {
+        super(factory);
+        this.exceptionHandler = exceptionHandler;
+        this.results = new ConcurrentResultArray<>(expectedSize);
+        join(promises, link);
+    }
+
+    @Override
+    protected K getKey(Map.Entry<K, Promise<V>> entry) {
+        return entry.getKey();
+    }
+
+    @Override
+    protected @NotNull Promise<V> getPromise(Map.Entry<K, Promise<V>> entry) {
+        return entry.getValue();
+    }
+
+    @Override
+    protected @Nullable Throwable onFinish(int index, K key, @NotNull PromiseCompletion<V> res) {
+        if (res.isError()) {
+            if (exceptionHandler == null) return res.getException();
+            exceptionHandler.accept(key, res.getException());
+        }
+
+        results.set(index, new AbstractMap.SimpleImmutableEntry<>(key, res.getResult()));
+        return null;
+    }
+
+    @Override
+    protected Map<K, V> getResult() {
+        List<Map.Entry<K, V>> list = results.toList();
+        Map<K, V> map = new HashMap<>(list.size());
+        for (Map.Entry<K, V> entry : list) {
+            map.put(entry.getKey(), entry.getValue());
+        }
+        return map;
+    }
+
+}