Use std::vector instead of std::deque in QAlertDispatcher

As we never use {push,pop}_front std::vector works here perfectly.
Also reserve memory for std::vector out of lock.

This could be considered as an optimization, but in reality this is just
using right container in right place. According to my measurements total
speedup is under 0.2%.

src/qtlibtorrent/alertdispatcher.cpp

@@ -33,12 +33,15 @@
 #include <boost/bind.hpp>
 #include <QMutexLocker>
 
+const size_t DEFAULT_ALERTS_CAPACITY = 32;
+
 QAlertDispatcher::QAlertDispatcher(libtorrent::session *session, QObject* parent)
   : QObject(parent)
   , m_session(session)
   , current_tag(new QAtomicPointer<QAlertDispatcher>(this))
   , event_posted(false)
 {
+  alerts.reserve(DEFAULT_ALERTS_CAPACITY);
   m_session->set_alert_dispatch(boost::bind(&QAlertDispatcher::dispatch, current_tag, _1));
 }
 
@@ -60,16 +63,18 @@ QAlertDispatcher::~QAlertDispatcher() {
   m_session->set_alert_dispatch(dispatch_function_t());
 }
 
-void QAlertDispatcher::getPendingAlertsNoWait(std::deque<libtorrent::alert*>& out) {
+void QAlertDispatcher::getPendingAlertsNoWait(std::vector<libtorrent::alert*>& out) {
   Q_ASSERT(out.empty());
+  out.reserve(DEFAULT_ALERTS_CAPACITY);
 
   QMutexLocker lock(&alerts_mutex);
   alerts.swap(out);
   event_posted = false;
 }
 
-void QAlertDispatcher::getPendingAlerts(std::deque<libtorrent::alert*>& out, unsigned long time) {
+void QAlertDispatcher::getPendingAlerts(std::vector<libtorrent::alert*>& out, unsigned long time) {
   Q_ASSERT(out.empty());
+  out.reserve(DEFAULT_ALERTS_CAPACITY);
 
   QMutexLocker lock(&alerts_mutex);
 

src/qtlibtorrent/alertdispatcher.h

@@ -46,8 +46,8 @@ public:
   QAlertDispatcher(libtorrent::session *session, QObject* parent);
   ~QAlertDispatcher();
 
-  void getPendingAlertsNoWait(std::deque<libtorrent::alert*>&);
+  void getPendingAlertsNoWait(std::vector<libtorrent::alert*>&);
-  void getPendingAlerts(std::deque<libtorrent::alert*>&, unsigned long time = ULONG_MAX);
+  void getPendingAlerts(std::vector<libtorrent::alert*>&, unsigned long time = ULONG_MAX);
 
 signals:
   void alertsReceived();
@@ -64,7 +64,7 @@ private:
   libtorrent::session *m_session;
   QMutex alerts_mutex;
   QWaitCondition alerts_condvar;
-  std::deque<libtorrent::alert*> alerts;
+  std::vector<libtorrent::alert*> alerts;
   QSharedPointer<QAtomicPointer<QAlertDispatcher> > current_tag;
   bool event_posted;
 };

src/qtlibtorrent/qbtsession.cpp

@@ -1649,7 +1649,7 @@ void QBtSession::saveFastResumeData() {
     } catch(libtorrent::invalid_handle&) {}
   }
   while (num_resume_data > 0) {
-    std::deque<alert*> alerts;
+    std::vector<alert*> alerts;
     m_alertDispatcher->getPendingAlerts(alerts, 30*1000);
     if (alerts.empty()) {
       std::cerr << " aborting with " << num_resume_data << " outstanding "
@@ -1657,7 +1657,7 @@ void QBtSession::saveFastResumeData() {
       break;
     }
 
-    for (std::deque<alert*>::const_iterator i = alerts.begin(), end = alerts.end(); i != end; ++i)
+    for (std::vector<alert*>::const_iterator i = alerts.begin(), end = alerts.end(); i != end; ++i)
     {
       alert const* a = *i;
       // Saving fastresume data can fail
@@ -2147,7 +2147,7 @@ void QBtSession::sendNotificationEmail(const QTorrentHandle &h) {
 // Read alerts sent by the Bittorrent session
 void QBtSession::readAlerts() {
 
-  typedef std::deque<alert*> alerts_t;
+  typedef std::vector<alert*> alerts_t;
   alerts_t alerts;
   m_alertDispatcher->getPendingAlertsNoWait(alerts);