common: persistent fork service

common/src/zygote.ts

@@ -4,6 +4,41 @@ import os from 'os';
 
 export type Zygote<T> = () => PluginFork<T>;
 
+export function createService<T, V>(options: ForkOptions, create: (t: Promise<T>) => Promise<V>): {
+    getResult: () => Promise<V>,
+    terminate: () => void,
+} {
+    let killed = false;
+    let currentResult: Promise<V>;
+    let currentFork: ReturnType<typeof sdk.fork<T>>;
+
+    return {
+        getResult() {
+            if (killed)
+                throw new Error('service terminated');
+
+            if (currentResult)
+                return currentResult;
+
+            currentFork = sdk.fork<T>(options);
+            currentFork.worker.on('exit', () => currentResult = undefined);
+            currentResult = create(currentFork.result);
+            currentResult.catch(() => currentResult = undefined);
+            return currentResult;
+        },
+
+        terminate() {
+            if (killed)
+                return;
+
+            killed = true;
+            currentFork.worker.terminate();
+            currentFork = undefined;
+            currentResult = undefined;
+        }
+    }
+}
+
 export function createZygote<T>(options?: ForkOptions): Zygote<T> {
     let zygote = sdk.fork<T>(options);
     function* next() {