Fix in-mem connector file operation racing condition

lib/connectors/memory.js

@@ -13,6 +13,7 @@ var geo = require('../geo');
 var utils = require('../utils');
 var fs = require('fs');
 var async = require('async');
+var debug = require('debug')('loopback:connector:memory');
 
 /**
  * Initialize the Memory connector against the given data source
@@ -104,45 +105,92 @@ Memory.prototype.collectionSeq = function(model, val) {
   return this.ids[model];
 };
 
-Memory.prototype.loadFromFile = function(callback) {
+/**
+ * Create a queue to serialize file read/write operations
+ * @returns {*} The file operation queue
+ */
+Memory.prototype.setupFileQueue = function() {
   var self = this;
+  if (!this.fileQueue) {
+    // Create a queue for writes
+    this.fileQueue = async.queue(function(task, done) {
+      var callback = task.callback || function() {};
+      var file = self.settings.file;
+      if (task.operation === 'write') {
+        // Flush out the models/ids
+        var data = JSON.stringify({
+          ids: self.ids,
+          models: self.cache,
+        }, null, '  ');
+        debug('Writing cache to %s: %s', file, data);
+        fs.writeFile(file, data, function(err) {
+          debug('Cache has been written to %s', file);
+          done(err);
+          callback(err, task.data);
+        });
+      } else if (task.operation === 'read') {
+        debug('Reading cache from %s: %s', file, data);
+        fs.readFile(file, {
+          encoding: 'utf8',
+          flag: 'r',
+        }, function(err, data) {
+          if (err && err.code !== 'ENOENT') {
+            done(err);
+            callback(err);
+          } else {
+            debug('Cache has been read from %s: %s', file, data);
+            self.parseAndLoad(data, function(err) {
+              done(err);
+              callback(err);
+            });
+          }
+        });
+      } else {
+        var err = new Error('Unknown type of task');
+        done(err);
+        callback(err);
+      }
+    }, 1);
+  }
+  return this.fileQueue;
+};
+
+Memory.prototype.parseAndLoad = function(data, callback) {
+  if (data) {
+    try {
+      data = JSON.parse(data.toString());
+    } catch (e) {
+      return callback && callback(e);
+    }
+
+    this.ids = data.ids || {};
+    this.cache = data.models || {};
+  } else {
+    if (!this.cache) {
+      this.ids = {};
+      this.cache = {};
+    }
+  }
+  callback && callback();
+};
+
+Memory.prototype.loadFromFile = function(callback) {
   var hasLocalStorage = typeof window !== 'undefined' && window.localStorage;
   var localStorage = hasLocalStorage && this.settings.localStorage;
 
-  if (self.settings.file) {
+  if (this.settings.file) {
-    fs.readFile(self.settings.file, {encoding: 'utf8', flag: 'r'}, function(err, data) {
+    debug('Queueing read %s', this.settings.file);
-      if (err && err.code !== 'ENOENT') {
+    this.setupFileQueue().push({
-        callback && callback(err);
+      operation: 'read',
-      } else {
+      callback: callback,
-        parseAndLoad(data);
-      }
     });
   } else if (localStorage) {
     var data = window.localStorage.getItem(localStorage);
     data = data || '{}';
-    parseAndLoad(data);
+    this.parseAndLoad(data, callback);
   } else {
     process.nextTick(callback);
   }
-
-  function parseAndLoad(data) {
-    if (data) {
-      try {
-        data = JSON.parse(data.toString());
-      } catch (e) {
-        return callback(e);
-      }
-
-      self.ids = data.ids || {};
-      self.cache = data.models || {};
-    } else {
-      if (!self.cache) {
-        self.ids = {};
-        self.cache = {};
-      }
-    }
-    callback && callback();
-  }
 };
 
 /*!
@@ -150,36 +198,22 @@ Memory.prototype.loadFromFile = function(callback) {
  * @param {Function} callback
  */
 Memory.prototype.saveToFile = function(result, callback) {
-  var self = this;
   var file = this.settings.file;
   var hasLocalStorage = typeof window !== 'undefined' && window.localStorage;
   var localStorage = hasLocalStorage && this.settings.localStorage;
   if (file) {
-    if (!self.writeQueue) {
+    debug('Queueing write %s', this.settings.file);
-      // Create a queue for writes
-      self.writeQueue = async.queue(function(task, cb) {
-        // Flush out the models/ids
-        var data = JSON.stringify({
-          ids: self.ids,
-          models: self.cache,
-        }, null, '  ');
-
-        fs.writeFile(self.settings.file, data, function(err) {
-          cb(err);
-          task.callback && task.callback(err, task.data);
-        });
-      }, 1);
-    }
     // Enqueue the write
-    self.writeQueue.push({
+    this.setupFileQueue().push({
+      operation: 'write',
       data: result,
       callback: callback,
     });
   } else if (localStorage) {
     // Flush out the models/ids
     var data = JSON.stringify({
-      ids: self.ids,
+      ids: this.ids,
-      models: self.cache,
+      models: this.cache,
     }, null, '  ');
     window.localStorage.setItem(localStorage, data);
     process.nextTick(function() {
@@ -506,7 +540,7 @@ function applyFilter(filter) {
       // Support referencesMany and other embedded relations
       // Also support array types. Mongo, possibly PostgreSQL
       if (Array.isArray(value)) {
-        var matcher  = where[key];
+        var matcher = where[key];
         // The following condition is for the case where we are querying with
         // a neq filter, and when the value is an empty array ([]).
         if (matcher.neq !== undefined && value.length <= 0) {

lib/datasource.js

@@ -365,36 +365,59 @@ DataSource.prototype.setup = function(name, settings) {
     }
   }
 
-  dataSource.connect = function(cb) {
+  dataSource.connect = function(callback) {
-    var dataSource = this;
+    callback = callback || utils.createPromiseCallback();
-    if (dataSource.connected || dataSource.connecting) {
+    var self = this;
-      process.nextTick(function() {
+    if (this.connected) {
-        cb && cb();
+      // The data source is already connected, return immediately
-      });
+      process.nextTick(callback);
-      return;
+      return callback.promise;
     }
-    dataSource.connecting = true;
+    if (typeof dataSource.connector.connect !== 'function') {
-    if (dataSource.connector.connect) {
+      // Connector doesn't have the connect function
-      dataSource.connector.connect(function(err, result) {
+      // Assume no connect is needed
-        if (!err) {
+      self.connected = true;
-          dataSource.connected = true;
+      self.connecting = false;
-          dataSource.connecting = false;
+      process.nextTick(function() {
-          dataSource.emit('connected');
+        self.emit('connected');
-        } else {
+        callback();
-          dataSource.connected = false;
+      });
-          dataSource.connecting = false;
+      return callback.promise;
-          dataSource.emit('error', err);
+    }
+
+    // Queue the callback
+    this.pendingConnectCallbacks = this.pendingConnectCallbacks || [];
+    this.pendingConnectCallbacks.push(callback);
+
+    // The connect is already in progress
+    if (this.connecting) return callback.promise;
+    // Set connecting flag to be true
+    this.connecting = true;
+    this.connector.connect(function(err, result) {
+      self.connecting = false;
+      if (!err) self.connected = true;
+      var cbs = self.pendingConnectCallbacks;
+      self.pendingConnectCallbacks = [];
+      if (!err) {
+        self.emit('connected');
+      } else {
+        self.emit('error', err);
+      }
+      // Invoke all pending callbacks
+      async.each(cbs, function(cb, done) {
+        try {
+          cb(err);
+        } catch (e) {
+          // Ignore error to make sure all callbacks are invoked
+          debug('Uncaught error raised by connect callback function: ', e);
+        } finally {
+          done();
         }
-        cb && cb(err, result);
+      }, function(err) {
+        if (err) throw err; // It should not happen
       });
-    } else {
+    });
-      process.nextTick(function() {
+    return callback.promise;
-        dataSource.connected = true;
-        dataSource.connecting = false;
-        dataSource.emit('connected');
-        cb && cb();
-      });
-    }
   };
 };
 

test/memory.test.js

@@ -34,8 +34,10 @@ describe('Memory connector', function() {
   });
 
   describe('with file', function() {
+    var ds;
+
     function createUserModel() {
-      var ds = new DataSource({
+      ds = new DataSource({
         connector: 'memory',
         file: file,
       });
@@ -62,6 +64,13 @@ describe('Memory connector', function() {
       User = createUserModel();
     });
 
+    it('should allow multiple connects', function(done) {
+      ds.connected = false; // Change the state to force reconnect
+      async.times(10, function(n, next) {
+        ds.connect(next);
+      }, done);
+    });
+
     it('should persist create', function(done) {
       var count = 0;
       async.eachSeries(['John1', 'John2', 'John3'], function(item, cb) {
@@ -76,6 +85,41 @@ describe('Memory connector', function() {
       }, done);
     });
 
+    /**
+     * This test depends on the `should persist create`, which creates 3
+     * records and saves into the `memory.json`. The following test makes
+     * sure existing records won't be loaded out of sequence to override
+     * newly created ones.
+     */
+    it('should not have out of sequence read/write', function(done) {
+      ds.connected = false;
+      ds.connector.connected = false; // Change the state to force reconnect
+      ds.connector.cache = {};
+
+      async.times(10, function(n, next) {
+        if (n === 10) {
+          // Make sure the connect finishes
+          return ds.connect(next);
+        }
+        ds.connect();
+        next();
+      }, function(err) {
+        async.eachSeries(['John4', 'John5'], function(item, cb) {
+          var count = 0;
+          User.create({name: item}, function(err, result) {
+            ids.push(result.id);
+            cb(err);
+          });
+        }, function(err) {
+          if (err) return done(err);
+          readModels(function(err, json) {
+            assert.equal(Object.keys(json.models.User).length, 5);
+            done();
+          });
+        });
+      });
+    });
+
     it('should persist delete', function(done) {
       // Now try to delete one
       User.deleteById(ids[0], function(err) {
@@ -86,7 +130,7 @@ describe('Memory connector', function() {
           if (err) {
             return done(err);
           }
-          assert.equal(Object.keys(json.models.User).length, 2);
+          assert.equal(Object.keys(json.models.User).length, 4);
           done();
         });
       });
@@ -101,7 +145,7 @@ describe('Memory connector', function() {
           if (err) {
             return done(err);
           }
-          assert.equal(Object.keys(json.models.User).length, 2);
+          assert.equal(Object.keys(json.models.User).length, 4);
           var user = JSON.parse(json.models.User[ids[1]]);
           assert.equal(user.name, 'John');
           assert(user.id === ids[1]);
@@ -120,7 +164,7 @@ describe('Memory connector', function() {
             if (err) {
               return done(err);
             }
-            assert.equal(Object.keys(json.models.User).length, 2);
+            assert.equal(Object.keys(json.models.User).length, 4);
             var user = JSON.parse(json.models.User[ids[1]]);
             assert.equal(user.name, 'John1');
             assert(user.id === ids[1]);
@@ -133,7 +177,7 @@ describe('Memory connector', function() {
     it('should load from the json file', function(done) {
       User.find(function(err, users) {
         // There should be 2 records
-        assert.equal(users.length, 2);
+        assert.equal(users.length, 4);
         done(err);
       });
     });