log catastrophic errors in getIndex, clean up comments

historyKeeper.js

@@ -229,9 +229,10 @@ module.exports.create = function (cfg) {
         as an added bonus:
         if the channel exists but its index does not then it caches the index
     */
-    const indexQueue = {};
+    const indexQueues = {};
     const getIndex = (ctx, channelName, cb) => {
         const chan = ctx.channels[channelName];
+        // if there is a channel in memory and it has an index cached, return it
         if (chan && chan.index) {
             // enforce async behaviour
             return void setTimeout(function () {
@@ -239,38 +240,35 @@ module.exports.create = function (cfg) {
             });
         }
 
-        // make a queue of callbacks in case getIndex is called before you
-        // compute and cache the index
-
         // if a call to computeIndex is already in progress for this channel
         // then add the callback for the latest invocation to the queue
         // and wait for it to complete
-        if (indexQueue[channelName]) {
-            indexQueue.channelName.push(cb);
+        if (Array.isArray(indexQueues[channelName])) {
+            indexQueues[channelName].push(cb);
             return;
         }
 
-        // if computeIndex is not already in progress, make an array
-        // with the current call first in line, so additional calls
-        // can add their callbacks to the queue
-        indexQueue[channelName] = (indexQueue[channelName] || []).push(cb);
+        // otherwise, make a queue for any 'getIndex' calls made before the following 'computeIndex' call completes
+        var queue = indexQueues[channelName] = (indexQueues[channelName] || [cb]);
 
         computeIndex(channelName, (err, ret) => {
-            // keep a local reference to this channel's queue
-            let queue = indexQueue[channelName];
+            if (!Array.isArray(queue)) {
+                // something is very wrong if there's no callback array
+                return void Log.error("E_INDEX_NO_CALLBACK", channelName);
+            }
+
 
-            // but remove it from the map of queues and not worry about cleaning up
-            // as long as computeIndex always calls back this won't be a memory leak
-            delete indexQueue[channelName];
+            // clean up the queue that you're about to handle, but keep a local copy
+            delete indexQueues[channelName];
 
+            // this is most likely an unrecoverable filesystem error
             if (err) {
                 // call back every pending function with the error
                 return void queue.forEach(function (_cb) {
                     _cb(err);
                 });
             }
-            // if there's a channel to use as a cache, store the result
-            // for future use
+            // cache the computed result if possible
             if (chan) { chan.index = ret; }
 
             // call back every pending function with the result