From 4abc4adde967bb27a4d36c62c95c6a20431ba4c5 Mon Sep 17 00:00:00 2001
From: Stephen Birarda <commit@birarda.com>
Date: Wed, 26 Oct 2016 16:18:12 -0700
Subject: [PATCH] add a timer to check for readyRead backup

---
 libraries/networking/src/udt/Socket.cpp | 22 ++++++++++++++++++++++
 libraries/networking/src/udt/Socket.h   |  3 +++
 2 files changed, 25 insertions(+)

diff --git a/libraries/networking/src/udt/Socket.cpp b/libraries/networking/src/udt/Socket.cpp
index 7ddbd54593..43bd7dd973 100644
--- a/libraries/networking/src/udt/Socket.cpp
+++ b/libraries/networking/src/udt/Socket.cpp
@@ -32,6 +32,7 @@ using namespace udt;
 Socket::Socket(QObject* parent, bool shouldChangeSocketOptions) :
     QObject(parent),
     _synTimer(new QTimer(this)),
+    _readyReadBackupTimer(new QTimer(this)),
     _shouldChangeSocketOptions(shouldChangeSocketOptions)
 {
     connect(&_udpSocket, &QUdpSocket::readyRead, this, &Socket::readPendingDatagrams);
@@ -46,6 +47,11 @@ Socket::Socket(QObject* parent, bool shouldChangeSocketOptions) :
     connect(&_udpSocket, SIGNAL(error(QAbstractSocket::SocketError)),
             this, SLOT(handleSocketError(QAbstractSocket::SocketError)));
     connect(&_udpSocket, &QAbstractSocket::stateChanged, this, &Socket::handleStateChanged);
+
+    // in order to help track down the zombie server bug, add a timer to check if we missed a readyRead
+    const int READY_READ_BACKUP_CHECK_MSECS = 10 * 1000;
+    connect(_readyReadBackupTimer, &QTimer::timeout, this, &Socket::checkForReadyReadBackup);
+    _readyReadBackupTimer->start(READY_READ_BACKUP_CHECK_MSECS);
 }
 
 void Socket::bind(const QHostAddress& address, quint16 port) {
@@ -296,9 +302,25 @@ void Socket::messageFailed(Connection* connection, Packet::MessageNumber message
     }
 }
 
+void Socket::checkForReadyReadBackup() {
+    if (_udpSocket.hasPendingDatagrams()) {
+        qCDebug(networking) << "Socket::checkForReadyReadBackup() detected blocked readyRead signal. Flushing pending datagrams.";
+
+        // drop all of the pending datagrams on the floor
+        while (_udpSocket.hasPendingDatagrams()) {
+            _udpSocket.readDatagram(nullptr, 0);
+        }
+    }
+}
+
 void Socket::readPendingDatagrams() {
     int packetSizeWithHeader = -1;
+
     while ((packetSizeWithHeader = _udpSocket.pendingDatagramSize()) != -1) {
+
+        // we're reading a packet so re-start the readyRead backup timer
+        _readyReadBackupTimer->start();
+
         // grab a time point we can mark as the receive time of this packet
         auto receiveTime = p_high_resolution_clock::now();
         
diff --git a/libraries/networking/src/udt/Socket.h b/libraries/networking/src/udt/Socket.h
index d65cb1406c..a811d78958 100644
--- a/libraries/networking/src/udt/Socket.h
+++ b/libraries/networking/src/udt/Socket.h
@@ -101,6 +101,7 @@ public slots:
     
 private slots:
     void readPendingDatagrams();
+    void checkForReadyReadBackup();
     void rateControlSync();
 
     void handleSocketError(QAbstractSocket::SocketError socketError);
@@ -136,6 +137,8 @@ private:
     int _synInterval { 10 }; // 10ms
     QTimer* _synTimer { nullptr };
 
+    QTimer* _readyReadBackupTimer { nullptr };
+
     int _maxBandwidth { -1 };
 
     std::unique_ptr<CongestionControlVirtualFactory> _ccFactory { new CongestionControlFactory<TCPVegasCC>() };