Add locking mechanism for tempfile operation

browser-version/browser-specific/lib/storage.js

@@ -81,6 +81,10 @@ function ensureDatafileIntegrity (filename, callback) {
   return callback(null);
 }
 
+// Nothing to do, no data corruption possible in the brower
+function waitForLock (filename, callback) {
+  return callback(null);
+}
 
 // Interface
 module.exports.exists = exists;
@@ -92,4 +96,4 @@ module.exports.readFile = readFile;
 module.exports.unlink = unlink;
 module.exports.mkdirp = mkdirp;
 module.exports.ensureDatafileIntegrity = ensureDatafileIntegrity;
-
+module.exports.waitForLock = waitForLock;

browser-version/out/nedb.js

@@ -3382,6 +3382,11 @@ function ensureDatafileIntegrity (filename, callback) {
   return callback(null);
 }
 
+// Nothing to do, no data corruption possible in the brower
+function waitForLock (filename, callback) {
+  return callback(null);
+}
+
 
 // Interface
 module.exports.exists = exists;
@@ -3393,6 +3398,7 @@ module.exports.readFile = readFile;
 module.exports.unlink = unlink;
 module.exports.mkdirp = mkdirp;
 module.exports.ensureDatafileIntegrity = ensureDatafileIntegrity;
+module.exports.waitForLock = waitForLock;
 
 
 },{"localforage":18}],13:[function(require,module,exports){

lib/storage.js

@@ -8,6 +8,7 @@
  */
 
 var fs = require('fs')
+  , lockfile = require('lockfile')
   , mkdirp = require('mkdirp')
   , async = require('async')
   , path = require('path')
@@ -21,7 +22,8 @@ storage.unlink = fs.unlink;
 storage.appendFile = fs.appendFile;
 storage.readFile = fs.readFile;
 storage.mkdirp = mkdirp;
-
+storage.lock = lockfile.lock;
+storage.unlock = lockfile.unlock;
 
 /**
  * Explicit name ...
@@ -73,6 +75,19 @@ storage.flushToStorage = function (options, callback) {
 };
 
 
+storage.waitForLock = function(filename, cb) {
+  var callback = cb || function () {};
+
+  storage.lock(filename, {retries: 5, retriesWait: 1}, function(err) {
+    if (err) {
+      storage.waitForLock(filename, cb);
+      return;
+    }
+
+    cb();
+  });
+};
+
 /**
  * Fully write or rewrite the datafile, immune to crashes during the write operation (data will not be lost)
  * @param {String} filename
@@ -81,28 +96,33 @@ storage.flushToStorage = function (options, callback) {
  */
 storage.crashSafeWriteFile = function (filename, data, cb) {
   var callback = cb || function () {}
-    , tempFilename = filename + '~';
-
-  async.waterfall([
-    async.apply(storage.flushToStorage, { filename: path.dirname(filename), isDir: true })
-  , function (cb) {
-      storage.exists(filename, function (exists) {
-        if (exists) {
-          storage.flushToStorage(filename, function (err) { return cb(err); });
-        } else {
-          return cb();
+    , tempFilename = filename + '~'
+    , lockFilename = filename + '.lock';
+
+  storage.waitForLock(lockFilename,
+    function() {
+      async.waterfall([
+        async.apply(storage.flushToStorage, { filename: path.dirname(filename), isDir: true })
+        , function (cb) {
+          storage.exists(filename, function (exists) {
+            if (exists) {
+              storage.flushToStorage(filename, function (err) { return cb(err); });
+            } else {
+              return cb();
+            }
+          });
         }
-      });
-    }
-  , function (cb) {
-      storage.writeFile(tempFilename, data, function (err) { return cb(err); });
-    }
-  , async.apply(storage.flushToStorage, tempFilename)
-  , function (cb) {
-      storage.rename(tempFilename, filename, function (err) { return cb(err); });
+        , function (cb) {
+          storage.writeFile(tempFilename, data, function (err) { return cb(err); });
+        }
+        , async.apply(storage.flushToStorage, tempFilename)
+        , function (cb) {
+          storage.rename(tempFilename, filename, function (err) { return cb(err); });
+        }
+        , async.apply(storage.flushToStorage, { filename: path.dirname(filename), isDir: true })
+      ], function (err) { storage.unlock(lockFilename); return callback(err); })
     }
-  , async.apply(storage.flushToStorage, { filename: path.dirname(filename), isDir: true })
-  ], function (err) { return callback(err); })
+  );
 };
 
 
@@ -112,23 +132,35 @@ storage.crashSafeWriteFile = function (filename, data, cb) {
  * @param {Function} callback signature: err
  */
 storage.ensureDatafileIntegrity = function (filename, callback) {
-  var tempFilename = filename + '~';
-
-  storage.exists(filename, function (filenameExists) {
-    // Write was successful
-    if (filenameExists) { return callback(null); }
-
-    storage.exists(tempFilename, function (oldFilenameExists) {
-      // New database
-      if (!oldFilenameExists) {
-        return storage.writeFile(filename, '', 'utf8', function (err) { callback(err); });
-      }
+  var tempFilename = filename + '~'
+    , lockFilename = filename + '.lock';
+
+  storage.waitForLock(lockFilename,
+    function() {
+      storage.exists(filename, function (filenameExists) {
+        // Write was successful
+        if (filenameExists) {
+          return callback(null);
+        }
 
-      // Write failed, use old version
-      storage.rename(tempFilename, filename, function (err) { return callback(err); });
-    });
-  });
-};
+        storage.exists(tempFilename, function (oldFilenameExists) {
+          // New database
+          if (!oldFilenameExists) {
+            return storage.writeFile(filename, '', 'utf8', function (err) {
+              callback(err);
+            });
+          }
+
+          // Write failed, use old version
+          storage.rename(tempFilename, filename, function (err) {
+            return callback(err);
+          });
+        });
+      });
+      storage.unlock(lockFilename);
+    }
+  );
+}
 
 
 

package.json

@@ -23,6 +23,7 @@
     "async": "0.2.10",
     "binary-search-tree": "0.2.5",
     "localforage": "^1.3.0",
+    "lockfile": "^1.0.4",
     "mkdirp": "~0.5.1",
     "underscore": "~1.4.4"
   },