Fix stack overflow in KernelHost.run()

This commit fixes issue aws#778.

packages/jsii-runtime/lib/host.ts

@@ -14,7 +14,7 @@ export class KernelHost {
             return; // done
         }
 
-        this.processRequest(req, () => this.run());
+        this.processRequest(req, () => setImmediate(() => this.run()));
     }
 
     private callbackHandler(callback: api.Callback) {

packages/jsii-runtime/package.json

@@ -10,7 +10,7 @@
   "scripts": {
     "build": "tsc --build && chmod +x bin/jsii-runtime && /bin/bash ./bundle.sh",
     "watch": "tsc --build -w",
-    "test": "/bin/bash test/playback-test.sh",
+    "test": "/bin/bash test/playback-test.sh && node test/stress-test.js",
     "package": "package-js"
   },
   "devDependencies": {

packages/jsii-runtime/test/stress-test.ts

@@ -0,0 +1,26 @@
+import { InputOutput, Input, Output } from "../lib/in-out";
+import { KernelHost } from "../lib/host";
+
+const requestCount = 250000;
+
+class FakeInputOutput extends InputOutput {
+    debug = false;
+    private count: number = 0;
+
+    write(_: Output) { }
+
+    read(): Input | undefined {
+        if(this.count == requestCount) {
+            return undefined;
+        }
+
+        ++this.count;
+        return { api: 'stats' };
+    }
+}
+
+const inout = new FakeInputOutput();
+const host = new KernelHost(inout, { debug: false, noStack: false });
+host.run();
+
+console.info("jsii-runtime stress test succeeded");