3 files changed, 59 insertions, 53 deletions
diff --git a/src/server/session/agents/message_router.ts b/src/server/session/agents/message_router.ts
index 5848e27ab..707f771d9 100644
--- a/src/server/session/agents/message_router.ts
+++ b/src/server/session/agents/message_router.ts
@@ -8,7 +8,7 @@ export default abstract class MessageRouter {
      * Add a listener at this message. When the monitor process
      * receives a message, it will invoke all registered functions.
      */
-    public addMessageListener = (name: string, handler: MessageHandler, exclusive = false) => {
+    public on = (name: string, handler: MessageHandler, exclusive = false) => {
         const handlers = this.onMessage[name];
         if (exclusive || !handlers) {
             this.onMessage[name] = [handler];
@@ -20,7 +20,7 @@ export default abstract class MessageRouter {
     /**
      * Unregister a given listener at this message.
      */
-    public removeMessageListener = (name: string, handler: MessageHandler) => {
+    public off = (name: string, handler: MessageHandler) => {
         const handlers = this.onMessage[name];
         if (handlers) {
             const index = handlers.indexOf(handler);
diff --git a/src/server/session/agents/monitor.ts b/src/server/session/agents/monitor.ts
index 5f4543606..ccba8199e 100644
--- a/src/server/session/agents/monitor.ts
+++ b/src/server/session/agents/monitor.ts
@@ -2,7 +2,7 @@ import { ExitHandler } from "./applied_session_agent";
 import { Configuration, configurationSchema, defaultConfig, Identifiers, colorMapping } from "../utilities/session_config";
 import Repl, { ReplAction } from "../utilities/repl";
 import { isWorker, setupMaster, on, Worker, fork } from "cluster";
-import { PromisifiedIPCManager, suffix, IPC, MessageHandler, Message } from "../utilities/ipc";
+import { PromisifiedIPCManager, suffix, IPC, MessageHandler } from "../utilities/ipc";
 import { red, cyan, white, yellow, blue } from "colors";
 import { exec, ExecOptions } from "child_process";
 import { validate, ValidationError } from "jsonschema";
@@ -40,8 +40,54 @@ export class Monitor extends MessageRouter {
         }
     }
 
-    public onCrashDetected = (listener: MessageHandler) => this.addMessageListener(Monitor.IntrinsicEvents.CrashDetected, listener);
-    public onServerRunning = (listener: MessageHandler) => this.addMessageListener(Monitor.IntrinsicEvents.ServerRunning, listener);
+    private constructor(sessionKey: string) {
+        super();
+        this.config = this.loadAndValidateConfiguration();
+        this.initialize(sessionKey);
+        this.repl = this.initializeRepl();
+    }
+
+    private initialize = (sessionKey: string) => {
+        console.log(this.timestamp(), cyan("initializing session..."));
+        this.key = sessionKey;
+
+        // determines whether or not we see the compilation / initialization / runtime output of each child server process
+        const output = this.config.showServerOutput ? "inherit" : "ignore";
+        setupMaster({ stdio: ["ignore", output, output, "ipc"] });
+
+        // handle exceptions in the master thread - there shouldn't be many of these
+        // the IPC (inter process communication) channel closed exception can't seem
+        // to be caught in a try catch, and is inconsequential, so it is ignored
+        process.on("uncaughtException", ({ message, stack }): void => {
+            if (message !== "Channel closed") {
+                this.mainLog(red(message));
+                if (stack) {
+                    this.mainLog(`uncaught exception\n${red(stack)}`);
+                }
+            }
+        });
+
+        // a helpful cluster event called on the master thread each time a child process exits
+        on("exit", ({ process: { pid } }, code, signal) => {
+            const prompt = `server worker with process id ${pid} has exited with code ${code}${signal === null ? "" : `, having encountered signal ${signal}`}.`;
+            this.mainLog(cyan(prompt));
+            // to make this a robust, continuous session, every time a child process dies, we immediately spawn a new one
+            this.spawn();
+        });
+    }
+
+    public finalize = (): void => {
+        if (this.finalized) {
+            throw new Error("Session monitor is already finalized");
+        }
+        this.finalized = true;
+        this.spawn();
+    }
+
+    public readonly hooks = Object.freeze({
+        crashDetected: (listener: MessageHandler<{ error: Error }>) => this.on(Monitor.IntrinsicEvents.CrashDetected, listener),
+        serverRunning: (listener: MessageHandler<{ isFirstTime: boolean }>) => this.on(Monitor.IntrinsicEvents.ServerRunning, listener)
+    });
 
     /**
      * Kill this session and its active child
@@ -91,48 +137,6 @@ export class Monitor extends MessageRouter {
         });
     }
 
-    private constructor(sessionKey: string) {
-        super();
-        console.log(this.timestamp(), cyan("initializing session..."));
-        this.key = sessionKey;
-        this.config = this.loadAndValidateConfiguration();
-
-        // determines whether or not we see the compilation / initialization / runtime output of each child server process
-        const output = this.config.showServerOutput ? "inherit" : "ignore";
-        setupMaster({ stdio: ["ignore", output, output, "ipc"] });
-
-        // handle exceptions in the master thread - there shouldn't be many of these
-        // the IPC (inter process communication) channel closed exception can't seem
-        // to be caught in a try catch, and is inconsequential, so it is ignored
-        process.on("uncaughtException", ({ message, stack }): void => {
-            if (message !== "Channel closed") {
-                this.mainLog(red(message));
-                if (stack) {
-                    this.mainLog(`uncaught exception\n${red(stack)}`);
-                }
-            }
-        });
-
-        // a helpful cluster event called on the master thread each time a child process exits
-        on("exit", ({ process: { pid } }, code, signal) => {
-            const prompt = `server worker with process id ${pid} has exited with code ${code}${signal === null ? "" : `, having encountered signal ${signal}`}.`;
-            this.mainLog(cyan(prompt));
-            // to make this a robust, continuous session, every time a child process dies, we immediately spawn a new one
-            this.spawn();
-        });
-
-        this.repl = this.initializeRepl();
-        Monitor.IPCManager.setRouter(this.route);
-    }
-
-    public finalize = (): void => {
-        if (this.finalized) {
-            throw new Error("Session monitor is already finalized");
-        }
-        this.finalized = true;
-        this.spawn();
-    }
-
     /**
      * Generates a blue UTC string associated with the time
      * of invocation.
@@ -282,8 +286,10 @@ export class Monitor extends MessageRouter {
         Monitor.IPCManager = IPC(this.activeWorker);
         this.mainLog(cyan(`spawned new server worker with process id ${this.activeWorker?.process.pid}`));
 
-        this.addMessageListener("kill", ({ args: { reason, graceful, errorCode } }) => this.killSession(reason, graceful, errorCode), true);
-        this.addMessageListener("lifecycle", ({ args: { event } }) => console.log(this.timestamp(), `${this.config.identifiers.worker.text} lifecycle phase (${event})`), true);
+        this.on("kill", ({ args: { reason, graceful, errorCode } }) => this.killSession(reason, graceful, errorCode), true);
+        this.on("lifecycle", ({ args: { event } }) => console.log(this.timestamp(), `${this.config.identifiers.worker.text} lifecycle phase (${event})`), true);
+
+        Monitor.IPCManager.setRouter(this.route);
     }
 
 }
diff --git a/src/server/session/agents/server_worker.ts b/src/server/session/agents/server_worker.ts
index 2c77cfb29..50abe398d 100644
--- a/src/server/session/agents/server_worker.ts
+++ b/src/server/session/agents/server_worker.ts
@@ -1,6 +1,6 @@
 import { ExitHandler } from "./applied_session_agent";
 import { isMaster } from "cluster";
-import { PromisifiedIPCManager } from "../utilities/ipc";
+import { PromisifiedIPCManager, Message } from "../utilities/ipc";
 import MessageRouter from "./message_router";
 import { red, green, white, yellow } from "colors";
 import { get } from "request-promise";
@@ -80,11 +80,11 @@ export class ServerWorker extends MessageRouter {
     private configureProcess = () => {
         ServerWorker.IPCManager.setRouter(this.route);
         // updates the local values of variables to the those sent from master
-        this.addMessageListener("updatePollingInterval", ({ args }) => {
+        this.on("updatePollingInterval", ({ args }: Message<{ newPollingIntervalSeconds: number }>) => {
             this.pollingIntervalSeconds = args.newPollingIntervalSeconds;
             return new Promise<void>(resolve => setTimeout(resolve, 1000 * 10));
         });
-        this.addMessageListener("manualExit", async ({ args: { isSessionEnd } }) => {
+        this.on("manualExit", async ({ args: { isSessionEnd } }: Message<{ isSessionEnd: boolean }>) => {
             await this.executeExitHandlers(isSessionEnd);
             process.exit(0);
         });
@@ -135,7 +135,7 @@ export class ServerWorker extends MessageRouter {
                     if (!this.shouldServerBeResponsive) {
                         // notify monitor thread that the server is up and running
                         this.lifecycleNotification(green(`listening on ${this.serverPort}...`));
-                        this.emitToMonitor(Monitor.IntrinsicEvents.ServerRunning, { firstTime: !this.isInitialized });
+                        this.emitToMonitor(Monitor.IntrinsicEvents.ServerRunning, { isFirstTime: !this.isInitialized });
                         this.isInitialized = true;
                     }
                     this.shouldServerBeResponsive = true;