Initial commit

src/infrastructure/Threading/AsyncLazy.ts

@@ -0,0 +1,34 @@
+import { Signal } from '../Events/Signal';
+
+export class AsyncLazy<T> {
+    private valueCreated = new Signal();
+    private isValueCreated = false;
+    private isCreatingValue = false;
+    private value: T | undefined;
+
+    constructor(private valueFactory: () => Promise<T>) { }
+
+    public setValueFactory(valueFactory: () => Promise<T>) {
+        this.valueFactory = valueFactory;
+    }
+
+    public async getValueAsync(): Promise<T> {
+        // If value is already created, return the value directly
+        if (this.isValueCreated) {
+            return Promise.resolve(this.value as T);
+        }
+        // If value is being created, wait until the value is created and then return it.
+        if (this.isCreatingValue) {
+            return new Promise<T>((resolve, reject) => {
+                // Return/result when valueCreated event is triggered.
+                this.valueCreated.on(() => resolve(this.value));
+            });
+        }
+        this.isCreatingValue = true;
+        this.value = await this.valueFactory();
+        this.isCreatingValue = false;
+        this.isValueCreated = true;
+        this.valueCreated.notify(null);
+        return Promise.resolve(this.value);
+    }
+}