Add a queue to setMetadata to aovid race conditions

rpc.js

@@ -340,6 +340,7 @@ var getMetadata = function (Env, channel, cb) {
         value: value
     }
 */
+var metadataSem = Saferphore.create(1);
 var setMetadata = function (Env, data, unsafeKey, cb) {
     var channel = data.channel;
     var command = data.command;
@@ -347,9 +348,17 @@ 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();
         getMetadata(Env, channel, function (err, metadata) {
-        if (err) { return void cb(err); }
-        if (!(metadata && Array.isArray(metadata.owners))) { return void cb('E_NO_OWNERS'); }
+            if (err) {
+                g();
+                return void cb(err);
+            }
+            if (!(metadata && Array.isArray(metadata.owners))) {
+                g();
+                return void cb('E_NO_OWNERS');
+            }
 
             // Confirm that the channel is owned by the user in question
             // or the user is accepting a pending ownerhsip offer
@@ -358,12 +367,15 @@ var setMetadata = function (Env, data, unsafeKey, cb) {
                         metadata.owners.indexOf(unsafeKey) === -1) {
 
                 // If you are a pending owner, make sure you can only add yourelf as an owner
-            if (command !== 'ADD_OWNERS' || !Array.isArray(data.value) || data.value.length !== 1
+                if (command !== 'ADD_OWNERS' || !Array.isArray(data.value)
+                        || data.value.length !== 1
                         || data.value[0] !== unsafeKey) {
+                    g();
                     return void cb('INSUFFICIENT_PERMISSIONS');
                 }
 
             } else if (metadata.owners.indexOf(unsafeKey) === -1) {
+                g();
                 return void cb('INSUFFICIENT_PERMISSIONS');
             }
 
@@ -372,16 +384,19 @@ var setMetadata = function (Env, data, unsafeKey, cb) {
             try {
                 Meta.handleCommand(metadata, line);
             } catch (e) {
+                g();
                 return void cb(e);
             }
 
-        return void Env.msgStore.writeMetadata(channel, JSON.stringify(line), function (e) {
+            Env.msgStore.writeMetadata(channel, JSON.stringify(line), function (e) {
+                g();
                 if (e) {
                     return void cb(e);
                 }
                 cb(void 0, metadata);
             });
         });
+    });
 };
 
 var getMultipleFileSize = function (Env, channels, cb) {