allow packages to block migration until they're ready

packages/livedata/livedata_connection.js

@@ -97,14 +97,14 @@ Meteor._LivedataConnection = function (url) {
       self.outstanding_methods = reload_data.outstanding_methods;
     // pending messages will be transmitted on initial stream 'reset'
   }
-  Meteor._reload.on_migrate(reload_key, function () {
+  Meteor._reload.on_migrate(reload_key, function (result) {
     var methods = _.map(self.outstanding_methods, function (m) {
       // filter out callback
       return {msg: m.msg};
     });
 
-    return { next_method_id: self.next_method_id,
-             outstanding_methods: methods };
+    result({ next_method_id: self.next_method_id,
+             outstanding_methods: methods });
   });
 
   // Setup stream

packages/reload/reload.js

@@ -68,16 +68,18 @@
   }
 
 
-  var save_callbacks = {};
+  var providers = [];
 
   ////////// External API //////////
 
   // Called by packages when they start up.
   // Registers a callback for when we want to save data.
-  // Before a reload, callback is called, and should return
-  // a JSONifyable object.
+  // Before a reload, callback is called. It takes one argument, a
+  // function. The package should wait until it is ready to migrate,
+  // and then call the function. If it has migration data, it should
+  // pass it to the function as a single JSON-compatible argument.
   Meteor._reload.on_migrate = function (name, callback) {
-    save_callbacks[name] = callback;
+    providers.push({name: name, callback: callback});
   };
 
   // Called by packages when they start up.
@@ -86,36 +88,55 @@
     return old_data[name];
   };
 
-  // Trigger a reload. Calls all the callbacks, saves all the values,
-  // then blows up the world.
+  // Trigger a reload. Starts a process that asynchronously calls all
+  // the callbacks, saves all the values, and then terminates this VM
+  // and starts a new one.
+  var reloading = false;
   Meteor._reload.reload = function () {
-    // Meteor._debug("Beginning hot reload.");
+    if (reloading)
+      return;
+    reloading = true;
 
-    // ask everyone for stuff to save
-    var new_data = {};
-    _.each(save_callbacks, function (callback, name) {
-      new_data[name] = callback();
-    });
+    // ask everyone for stuff to save, asynchronously
+    var migration_data = {};
+    var remaining = _.clone(providers);
+    var requestNext = function () {
+      var next = remaining.shift();
+      if (!next)
+        saveAndRestart();
+      else
+        next.callback(function (value) {
+          if (value !== undefined)
+            migration_data[next.name] = value;
+          requestNext();
+        });
+    };
 
-    var new_json;
-    try {
-      new_json = JSON.stringify({
-        time: (new Date()).getTime(), data: new_data, reload: true
-      });
-    } catch (err) {
-      Meteor._debug("Asked to persist non-JSONable data. Ignoring.");
-      new_json = '{}';
-    }
+    // then persist the migration data and restart
+    var saveAndRestart = function () {
+      var json;
+      try {
+        json = JSON.stringify({
+          time: (new Date()).getTime(), data: migration_data, reload: true
+        });
+      } catch (err) {
+        Meteor._debug("Asked to persist non-JSONable data. Ignoring.");
+        json = '{}';
+      }
 
-    // save it
-    if (typeof sessionStorage !== "undefined") {
-        sessionStorage.setItem(KEY_NAME, new_json);
-    } else {
-      Meteor._debug("Browser does not support sessionStorage. Not saving reload state.");
-    }
+      // save it
+      if (typeof sessionStorage !== "undefined") {
+        sessionStorage.setItem(KEY_NAME, json);
+      } else {
+        Meteor._debug("Browser does not support sessionStorage. Not saving reload state.");
+      }
 
-    // blow up the world!
-    window.location.reload();
+      // Restart with the new code.
+      window.location.reload();
+    };
+
+    // kick off asynchronous process
+    requestNext();
   };
 
 })();

packages/session/session.js

@@ -105,9 +105,9 @@ Session = _.extend({}, {
 
 
 if (Meteor._reload) {
-  Meteor._reload.on_migrate('session', function () {
+  Meteor._reload.on_migrate('session', function (result) {
     // XXX sanitize and make sure it's JSONible?
-    return { keys: Session.keys };
+    result({keys: Session.keys});
   });
 
   (function () {

packages/stream/stream_client.js

@@ -130,21 +130,21 @@ _.extend(Meteor._Stream.prototype, {
     // inspect the welcome data and decide if we have to reload
     try {
       var welcome_data = JSON.parse(welcome_message);
-      if (welcome_data && welcome_data.server_id) {
-        if (self.server_id && self.server_id !== welcome_data.server_id) {
-          Meteor._reload.reload();
-          // world's about to end, just leave the connection 'connecting'
-          // until it does.
-          return;
-        }
-        self.server_id = welcome_data.server_id;
-      } else {
-        Meteor._debug("DEBUG: invalid welcome packet", welcome_data);
-      }
     } catch (err) {
       Meteor._debug("DEBUG: malformed welcome packet", welcome_message);
     }
 
+    if (welcome_data && welcome_data.server_id) {
+      if (self.server_id && self.server_id !== welcome_data.server_id) {
+        Meteor._reload.reload();
+        // world's about to end, just leave the connection 'connecting'
+        // until it does.
+        return;
+      }
+      self.server_id = welcome_data.server_id;
+    } else
+      Meteor._debug("DEBUG: invalid welcome packet", welcome_data);
+
     // update status
     self.current_status.status = "connected";
     self.current_status.connected = true;