run upto 5 apptasks in parallel

fixes #482

src/locker.js

@@ -9,6 +9,7 @@ function Locker() {
     this._operation = null;
     this._timestamp = null;
     this._watcherId = -1;
+    this._lockDepth = 0; // recursive locks
 }
 util.inherits(Locker, EventEmitter);
 
@@ -24,6 +25,7 @@ Locker.prototype.lock = function (operation) {
     if (this._operation !== null) return new Error('Already locked for ' + this._operation);
 
     this._operation = operation;
+    ++this._lockDepth;
     this._timestamp = new Date();
     var that = this;
     this._watcherId = setInterval(function () { debug('Lock unreleased %s', that._operation); }, 1000 * 60 * 5);
@@ -35,17 +37,31 @@ Locker.prototype.lock = function (operation) {
     return null;
 };
 
+Locker.prototype.recursiveLock = function (operation) {
+    if (this._operation === operation) {
+        ++this._lockDepth;
+        debug('Re-acquired : %s Depth : %s', this._operation, this._lockDepth);
+        return null;
+    }
+
+    return this.lock(operation);
+};
+
 Locker.prototype.unlock = function (operation) {
     assert.strictEqual(typeof operation, 'string');
 
     if (this._operation !== operation) throw new Error('Mismatched unlock. Current lock is for ' + this._operation); // throw because this is a programming error
 
-    debug('Released : %s', this._operation);
+    if (--this._lockDepth === 0) {
+        debug('Released : %s', this._operation);
 
-    this._operation = null;
-    this._timestamp = null;
-    clearInterval(this._watcherId);
-    this._watcherId = -1;
+        this._operation = null;
+        this._timestamp = null;
+        clearInterval(this._watcherId);
+        this._watcherId = -1;
+    } else {
+        debug('Recursive lock released : %s. Depth : %s', this._operation, this._lockDepth);
+    }
 
     this.emit('unlocked', operation);
 

src/taskmanager.js

@@ -17,10 +17,7 @@ var appdb = require('./appdb.js'),
 var gActiveTasks = { };
 var gPendingTasks = [ ];
 
-// Task concurrency is 1 for two reasons:
-// 1. The backup scripts (app and box) turn off swap after finish disregarding other backup processes
-// 2. apptask getFreePort has race with multiprocess
-var TASK_CONCURRENCY = 1;
+var TASK_CONCURRENCY = 5;
 var NOOP_CALLBACK = function (error) { console.error(error); };
 
 function initialize(callback) {
@@ -54,7 +51,8 @@ function uninitialize(callback) {
 
 function startNextTask() {
     if (gPendingTasks.length === 0) return;
-    assert.strictEqual(Object.keys(gActiveTasks).length, 0); // since we allow only one task at a time
+
+    assert(Object.keys(gActiveTasks).length < TASK_CONCURRENCY);
 
     startAppTask(gPendingTasks.shift());
 }
@@ -63,7 +61,7 @@ function startAppTask(appId) {
     assert.strictEqual(typeof appId, 'string');
     assert(!(appId in gActiveTasks));
 
-    var lockError = locker.lock(locker.OP_APPTASK);
+    var lockError = locker.recursiveLock(locker.OP_APPTASK);
 
     if (lockError || Object.keys(gActiveTasks).length >= TASK_CONCURRENCY) {
         debug('Reached concurrency limit, queueing task for %s', appId);