Add an init watchdog for extension workers

If an extension worker does not complete initialization in a reasonable
amount of time (currently 15 seconds) then the worker will be
terminated. A complete initialization includes registering an extension.

src/dispatch/central-dispatch.js

@@ -38,7 +38,7 @@ class CentralDispatch extends SharedDispatch {
     /**
      * Set a local object as the global provider of the specified service.
      * WARNING: Any method on the provider can be called from any worker within the dispatch system.
-     * @param {string} service - a globally unique string identifying this service. Examples: 'vm', 'gui', 'extension9'.
+     * @param {string} service - a globally unique string identifying this service. Examples: 'vm', 'gui'.
      * @param {object} provider - a local object which provides this service.
      * @returns {Promise} - a promise which will resolve once the service is registered.
      */
@@ -72,6 +72,25 @@ class CentralDispatch extends SharedDispatch {
         }
     }
 
+    /**
+     * Remove a service provider from the central dispatch service, un-registering any services it provides.
+     * If the provider is a worker its dispatch service will be shut down.
+     * The worker itself will NOT be terminated by this call.
+     * @param {Worker|object} provider - the worker or object instance to be removed.
+     */
+    removeProvider (provider) {
+        const workerIndex = this.workers.indexOf(provider);
+        if (workerIndex !== -1) {
+            /** @TODO Should we ask the worker to shut down? If so, owner must wait before terminating the worker. */
+            this.workers.splice(workerIndex, 1);
+        }
+        for (const serviceName in Object.keys(this.services)) {
+            if (this.services[serviceName] === provider) {
+                delete this.services[serviceName];
+            }
+        }
+    }
+
     /**
      * Fetch the service provider object for a particular service name.
      * @override

src/dispatch/shared-dispatch.js

@@ -39,6 +39,24 @@ class SharedDispatch {
          * @type {int}
          */
         this.nextResponseId = 0;
+
+        /**
+         * While processing a call in _onMessage, this will be set to the originating object.
+         * At all other times it will be null.
+         * @type {object}
+         * @private
+         */
+        this._callingWorker = null;
+    }
+
+    /**
+     * Central dispatch: while processing a call from a worker, this will be set to the worker originating that call.
+     * Worker dispatch: while processing a call from the main thread, this will be set to the global object.
+     * At all other times it will be null.
+     * @returns {object} - the worker originating the current call, if any.
+     */
+    get callingWorker () {
+        return this._callingWorker;
     }
 
     /**
@@ -184,10 +202,15 @@ class SharedDispatch {
         message.args = message.args || [];
         let promise;
         if (message.service) {
-            if (message.service === 'dispatch') {
-                promise = this._onDispatchMessage(worker, message);
-            } else {
-                promise = this.call(message.service, message.method, ...message.args);
+            try {
+                this._callingWorker = worker;
+                if (message.service === 'dispatch') {
+                    promise = this._onDispatchMessage(worker, message);
+                } else {
+                    promise = this.call(message.service, message.method, ...message.args);
+                }
+            } finally {
+                this._callingWorker = null;
             }
         } else if (typeof message.responseId === 'undefined') {
             log.error(`Dispatch caught malformed message from a worker: ${JSON.stringify(event)}`);

src/extension-support/extension-manager.js

@@ -70,6 +70,14 @@ class ExtensionManager {
          */
         this.pendingWorkers = [];
 
+        /**
+         * Set of workers currently being monitored by `_startWorkerWatchdog`.
+         * @see {_startWorkerWatchdog}
+         * @type {Set.<object>}
+         * @private
+         */
+        this._activeWatchdogs = new Set();
+
         /**
          * Keep a reference to the runtime so we can construct internal extension objects.
          * TODO: remove this in favor of extensions accessing the runtime as a service.
@@ -99,7 +107,10 @@ class ExtensionManager {
             const ExtensionWorker = require('worker-loader?name=extension-worker.js!./extension-worker');
 
             this.pendingExtensions.push({extensionURL, resolve, reject});
-            dispatch.addWorker(new ExtensionWorker());
+
+            const worker = new ExtensionWorker();
+            dispatch.addWorker(worker);
+            this._startWorkerWatchdog(worker);
         });
     }
 
@@ -110,16 +121,28 @@ class ExtensionManager {
         return [id, workerInfo.extensionURL];
     }
 
+    /**
+     * Collect extension metadata from the specified service and begin the extension registration process.
+     * @param {string} serviceName - the name of the service hosting the extension.
+     */
     registerExtensionService (serviceName) {
         dispatch.call(serviceName, 'getInfo').then(info => {
             this._registerExtensionInfo(serviceName, info);
         });
     }
 
+    /**
+     * Called by an extension worker to indicate that the worker has finished initialization.
+     * @param {int} id - the worker ID.
+     * @param {*?} e - the error encountered during initialization, if any.
+     */
     onWorkerInit (id, e) {
         const workerInfo = this.pendingWorkers[id];
         delete this.pendingWorkers[id];
         if (e) {
+            log.warn(`Extension manager forcibly terminating worker for extension with ID ${id}, URL ${
+                workerInfo.extensionURL} due to error during initialization`);
+            workerInfo.worker.terminate();
             workerInfo.reject(e);
         } else {
             workerInfo.resolve(id);
@@ -133,16 +156,29 @@ class ExtensionManager {
      */
     _registerInternalExtension (extensionObject) {
         const extensionInfo = extensionObject.getInfo();
-        const serviceName = `extension.internal.${extensionInfo.id}`;
+        const fakeWorkerId = this.nextExtensionWorker++;
+        const serviceName = `extension.${fakeWorkerId}.${extensionInfo.id}`;
         return dispatch.setService(serviceName, extensionObject)
             .then(() => dispatch.call('extensions', 'registerExtensionService', serviceName));
     }
 
+    /**
+     * Sanitize extension info then register its primitives with the VM.
+     * @param {string} serviceName - the name of the service hosting the extension
+     * @param {ExtensionInfo} extensionInfo - the extension's metadata
+     * @private
+     */
     _registerExtensionInfo (serviceName, extensionInfo) {
         extensionInfo = this._prepareExtensionInfo(serviceName, extensionInfo);
-        dispatch.call('runtime', '_registerExtensionPrimitives', extensionInfo).catch(e => {
-            log.error(`Failed to register primitives for extension on service ${serviceName}: ${JSON.stringify(e)}`);
-        });
+        dispatch.call('runtime', '_registerExtensionPrimitives', extensionInfo).then(
+            () => {
+                if (dispatch.callingWorker) {
+                    this._stopWorkerWatchdog(dispatch.callingWorker);
+                }
+            },
+            e => {
+                log.error(`Failed to register primitives for extension "${extensionInfo.id}": ${e.message}`);
+            });
     }
 
     /**
@@ -211,6 +247,35 @@ class ExtensionManager {
         }
         return blockInfo;
     }
+
+    /**
+     * Start a watchdog to terminate this worker unless it registers an extension before the timeout.
+     * @param {object} worker - the worker to watch.
+     * @private
+     */
+    _startWorkerWatchdog (worker) {
+        const timeout = 5 * 1000; // 5 seconds
+
+        this._activeWatchdogs.add(worker);
+        setTimeout(() => {
+            if (this._activeWatchdogs.has(worker)) {
+                this._activeWatchdogs.delete(worker);
+                log.warn(`Worker watchdog timed out. Terminating worker.`);
+                dispatch.removeProvider(worker);
+                worker.terminate();
+            }
+        }, timeout);
+    }
+
+    /**
+     * Mark this worker as "safe" from the watchdog.
+     * @param {object} worker - the worker to mark as safe.
+     * @see {_startWorkerWatchdog}
+     * @private
+     */
+    _stopWorkerWatchdog (worker) {
+        this._activeWatchdogs.delete(worker);
+    }
 }
 
 module.exports = ExtensionManager;