Simplify extension duplication prevention station

Since we will only have builtin extensions for a while, the
more-complicated, watchdog-based extension duplication prevention has
been replaced with one that treats the extension URL as equivalent to
the extension ID. This is true only for built-in extensions, so once we
start supporting third-party extensions we will likely need to bring
back the watchdog (commit e4381b4693) and
the more-complex duplication prevention (commit
670e51d335).

The code here should be treated as a last resort: ideally the GUI should
check if a particular extension is loaded (maybe by calling the
Extension Manager's new `isExtensionLoaded` method) and avoid calling
`loadExtensionURL` if it is.

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'.
+     * @param {string} service - a globally unique string identifying this service. Examples: 'vm', 'gui', 'extension9'.
      * @param {object} provider - a local object which provides this service.
      * @returns {Promise} - a promise which will resolve once the service is registered.
      */
@@ -55,19 +55,6 @@ class CentralDispatch extends SharedDispatch {
         }
     }
 
-    /**
-     * Unregister a service without regard to which object or worker might provide it.
-     * @param {string} service - the globally unique string provided to `setService` when the service was registered.
-     * @see {setService}
-     */
-    clearService (service) {
-        if (this.services.hasOwnProperty(service)) {
-            delete this.services[service];
-        } else {
-            log.warn(`Central dispatch can't clear unknown service ${service}`);
-        }
-    }
-
     /**
      * Add a worker to the message dispatch system. The worker must implement a compatible message dispatch framework.
      * The dispatcher will immediately attempt to "handshake" with the worker.
@@ -85,25 +72,6 @@ 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

@@ -39,24 +39,6 @@ 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;
     }
 
     /**
@@ -202,15 +184,10 @@ class SharedDispatch {
         message.args = message.args || [];
         let promise;
         if (message.service) {
-            try {
+            if (message.service === 'dispatch') {
-                this._callingWorker = worker;
+                promise = this._onDispatchMessage(worker, message);
-                if (message.service === 'dispatch') {
+            } else {
-                    promise = this._onDispatchMessage(worker, message);
+                promise = this.call(message.service, message.method, ...message.args);
-                } 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

@@ -71,20 +71,12 @@ class ExtensionManager {
         this.pendingWorkers = [];
 
         /**
-         * Set of loaded extension IDs. For built-in extensions the "URL" is the same as the ID; they differ in general.
+         * Set of loaded extension URLs/IDs (equivalent for built-in extensions).
          * @type {Set.<string>}
          * @private
          */
         this._loadedExtensions = new Set();
 
-        /**
-         * 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.
@@ -101,7 +93,7 @@ class ExtensionManager {
      * Check whether an extension is registered or is in the process of loading. This is intended to control loading or
      * adding extensions so it may return `true` before the extension is ready to be used. Use the promise returned by
      * `loadExtensionURL` if you need to wait until the extension is truly ready.
-     * @param {string} extensionID - the ID (not URL) of the extension.
+     * @param {string} extensionID - the ID of the extension.
      * @returns {boolean} - true if loaded, false otherwise.
      */
     isExtensionLoaded (extensionID) {
@@ -115,6 +107,13 @@ class ExtensionManager {
      */
     loadExtensionURL (extensionURL) {
         if (builtinExtensions.hasOwnProperty(extensionURL)) {
+            /** @TODO dupe handling for non-builtin extensions. See commit 670e51d33580e8a2e852b3b038bb3afc282f81b9 */
+            if (this.isExtensionLoaded(extensionURL)) {
+                const message = `Rejecting attempt to load a second extension with ID ${extensionURL}`;
+                log.warn(message);
+                return Promise.reject(new Error(message));
+            }
+
             const extension = builtinExtensions[extensionURL];
             const extensionInstance = new extension(this.runtime);
             return this._registerInternalExtension(extensionInstance);
@@ -125,10 +124,7 @@ 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);
         });
     }
 
@@ -158,9 +154,6 @@ class ExtensionManager {
         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);
@@ -188,22 +181,9 @@ class ExtensionManager {
      */
     _registerExtensionInfo (serviceName, extensionInfo) {
         extensionInfo = this._prepareExtensionInfo(serviceName, extensionInfo);
-        if (this.isExtensionLoaded(extensionInfo.id)) {
+        dispatch.call('runtime', '_registerExtensionPrimitives', extensionInfo).catch(e => {
-            const message = `Ignoring attempt to load a second extension with ID ${extensionInfo.id}`;
+            log.error(`Failed to register primitives for extension on service ${serviceName}: ${JSON.stringify(e)}`);
-            log.warn(message);
+        });
-            dispatch.clearService(serviceName);
-        } else {
-            dispatch.call('runtime', '_registerExtensionPrimitives', extensionInfo).then(
-                () => {
-                    this._loadedExtensions.add(extensionInfo.id);
-                    if (dispatch.callingWorker) {
-                        this._stopWorkerWatchdog(dispatch.callingWorker);
-                    }
-                },
-                e => {
-                    log.error(`Failed to register primitives for extension "${extensionInfo.id}": ${e.message}`);
-                });
-        }
     }
 
     /**
@@ -272,35 +252,6 @@ 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;