implement per-channel fifo queues for metadata and channel writes

historyKeeper.js

@@ -7,6 +7,7 @@ const Nacl = require('tweetnacl');
 const Crypto = require('crypto');
 const Once = require("./lib/once");
 const Meta = require("./lib/metadata");
+const WriteQueue = require("./lib/write-queue");
 
 let Log;
 const now = function () { return (new Date()).getTime(); };
@@ -302,20 +303,13 @@ module.exports.create = function (cfg) {
         * the fix is to use callbacks and implement queueing for writes
           * to guarantee that offset computation is always atomic with writes
     */
-    const storageQueues = {};
+    const queueStorage = WriteQueue();
 
-    const storeQueuedMessage = function (ctx, queue, id) {
-        if (queue.length === 0) {
-            delete storageQueues[id];
-            return;
-        }
-
-        const first = queue.shift();
-
-        const msgBin = first.msg;
-        const optionalMessageHash = first.hash;
-        const isCp = first.isCp;
+    const storeMessage = function (ctx, channel, msg, isCp, optionalMessageHash) {
+        const id = channel.id;
+        const msgBin = new Buffer(msg + '\n', 'utf8');
 
+        queueStorage(id, function (next) {
             // Store the message first, and update the index only once it's stored.
             // store.messageBin can be async so updating the index first may
             // result in a wrong cpIndex
@@ -331,8 +325,7 @@ module.exports.create = function (cfg) {
 
                         // TODO make it possible to respond to clients with errors so they know
                         // their message wasn't stored
-                    storeQueuedMessage(ctx, queue, id);
-                    return;
+                        return void next();
                     }
                 }));
             }).nThen((waitFor) => {
@@ -340,10 +333,7 @@ module.exports.create = function (cfg) {
                     if (err) {
                         Log.warn("HK_STORE_MESSAGE_INDEX", err.stack);
                         // non-critical, we'll be able to get the channel index later
-
-                    // proceed to the next message in the queue
-                    storeQueuedMessage(ctx, queue, id);
-                    return;
+                        return void next();
                     }
                     if (typeof (index.line) === "number") { index.line++; }
                     if (isCp) {
@@ -362,28 +352,10 @@ module.exports.create = function (cfg) {
                     index.size += msgBin.length;
 
                     // handle the next element in the queue
-                storeQueuedMessage(ctx, queue, id);
+                    next();
                 }));
             });
-    };
-
-    const storeMessage = function (ctx, channel, msg, isCp, optionalMessageHash) {
-        const id = channel.id;
-
-        const msgBin = new Buffer(msg + '\n', 'utf8');
-        if (Array.isArray(storageQueues[id])) {
-            return void storageQueues[id].push({
-                msg: msgBin,
-                hash: optionalMessageHash,
-                isCp: isCp,
         });
-        }
-
-        const queue = storageQueues[id] = (storageQueues[id] || [{
-            msg: msgBin,
-            hash: optionalMessageHash,
-        }]);
-        storeQueuedMessage(ctx, queue, id);
     };
 
     var CHECKPOINT_PATTERN = /^cp\|(([A-Za-z0-9+\/=]+)\|)?/;

lib/write-queue.js

@@ -0,0 +1,40 @@
+/*
+var q = Queue();
+q(id, function (next) {
+    // whatever you need to do....
+
+    // when you're done
+    next();
+});
+*/
+
+var fix1 = function (f, x) {
+    return function () { f(x); };
+};
+
+module.exports = function () {
+    var map = {};
+
+    var next = function (id) {
+        if (map[id] && map[id].length === 0) { return void delete map[id]; }
+        var task = map[id].shift();
+        task(fix1(next, id));
+    };
+
+    return function (id, task) {
+        // support initialization with just a function
+        if (typeof(id) === 'function' && typeof(task) === 'undefined') {
+            task = id;
+            id = '';
+        }
+        // ...but you really need to pass a function
+        if (typeof(task) !== 'function') { throw new Error("Expected function"); }
+
+        // if the intended queue already has tasks in progress, add this one to the end of the queue
+        if (map[id]) { return void map[id].push(task); }
+
+        // otherwise create a queue containing the given task
+        map[id] = [task];
+        next(id);
+    };
+};

rpc.js

@@ -18,7 +18,7 @@ const nThen = require("nthen");
 const getFolderSize = require("get-folder-size");
 const Pins = require("./lib/pins");
 const Meta = require("./lib/metadata");
-
+const WriteQueue = require("./lib/write-queue");
 
 var RPC = module.exports;
 
@@ -340,8 +340,7 @@ var getMetadata = function (Env, channel, cb) {
         value: value
     }
 */
-// XXX global saferphore may cause issues here, a queue "per channel" is probably better
-var metadataSem = Saferphore.create(1);
+var queueMetadata = WriteQueue();
 var setMetadata = function (Env, data, unsafeKey, cb) {
     var channel = data.channel;
     var command = data.command;
@@ -349,16 +348,15 @@ var setMetadata = function (Env, data, unsafeKey, cb) {
     if (!command || typeof (command) !== 'string') { return void cb ('INVALID_COMMAND'); }
     if (Meta.commands.indexOf(command) === -1) { return void('UNSUPPORTED_COMMAND'); }
 
-    metadataSem.take(function (give) {
-        var g = give();
+    queueMetadata(channel, function (next) {
         getMetadata(Env, channel, function (err, metadata) {
             if (err) {
-                g();
-                return void cb(err);
+                cb(err);
+                return void next();
             }
             if (!(metadata && Array.isArray(metadata.owners))) {
-                g();
-                return void cb('E_NO_OWNERS');
+                cb('E_NO_OWNERS');
+                return void next();
             }
 
             // Confirm that the channel is owned by the user in question
@@ -372,13 +370,13 @@ var setMetadata = function (Env, data, unsafeKey, cb) {
                         || !Array.isArray(data.value)
                         || data.value.length !== 1
                         || data.value[0] !== unsafeKey) {
-                    g();
-                    return void cb('INSUFFICIENT_PERMISSIONS');
+                    cb('INSUFFICIENT_PERMISSIONS');
+                    return void next();
                 }
 
             } else if (metadata.owners.indexOf(unsafeKey) === -1) {
-                g();
-                return void cb('INSUFFICIENT_PERMISSIONS');
+                cb('INSUFFICIENT_PERMISSIONS');
+                return void next();
             }
 
             // Add the new metadata line
@@ -387,22 +385,23 @@ var setMetadata = function (Env, data, unsafeKey, cb) {
             try {
                 changed = Meta.handleCommand(metadata, line);
             } catch (e) {
-                g();
-                return void cb(e);
+                cb(e);
+                return void next();
             }
 
             // if your command is valid but it didn't result in any change to the metadata,
             // call back now and don't write any "useless" line to the log
             if (!changed) {
-                g();
-                return void cb(void 0, metadata);
+                cb(void 0, metadata);
+                return void next();
             }
             Env.msgStore.writeMetadata(channel, JSON.stringify(line), function (e) {
-                g();
                 if (e) {
-                    return void cb(e);
+                    cb(e);
+                    return void next();
                 }
                 cb(void 0, metadata);
+                next();
             });
         });
     });