Reduce CPU usage from background PC polling

app/backend/computermanager.cpp

@@ -29,9 +29,9 @@ public:
     }
 
 private:
-    bool tryPollComputer(NvAddress address, bool& changed)
+    bool tryPollComputer(QNetworkAccessManager* nam, NvAddress address, bool& changed)
     {
-        NvHTTP http(address, 0, m_Computer->serverCert);
+        NvHTTP http(address, 0, m_Computer->serverCert, nam);
 
         QString serverInfo;
         try {
@@ -52,9 +52,9 @@ private:
         return true;
     }
 
-    bool updateAppList(bool& changed)
+    bool updateAppList(QNetworkAccessManager* nam, bool& changed)
     {
-        NvHTTP http(m_Computer);
+        NvHTTP http(m_Computer, nam);
 
         QVector<NvApp> appList;
 
@@ -81,6 +81,14 @@ private:
         setServiceLevel(QThread::QualityOfService::Eco);
 #endif
 
+        // Share the QNetworkAccessManager to conserve resources when polling.
+        // Each instance creates a worker thread, so sharing them ensures that
+        // we are not spamming a new thread for every single polling attempt.
+        //
+        // Since QThread inherit the priority of the current thread, this also
+        // ensures that the NAM's worker thread will inherit our lower priority.
+        QNetworkAccessManager nam;
+
         // Always fetch the applist the first time
         int pollsSinceLastAppListFetch = POLLS_PER_APPLIST_FETCH;
         while (!isInterruptionRequested()) {
@@ -93,7 +101,7 @@ private:
                         return;
                     }
 
-                    if (tryPollComputer(address, stateChanged)) {
+                    if (tryPollComputer(&nam, address, stateChanged)) {
                         if (!wasOnline) {
                             qInfo() << m_Computer->name << "is now online at" << m_Computer->activeAddress.toString();
                         }
@@ -124,7 +132,7 @@ private:
                     stateChanged = false;
                 }
 
-                if (updateAppList(stateChanged)) {
+                if (updateAppList(&nam, stateChanged)) {
                     pollsSinceLastAppListFetch = 0;
                 }
             }

app/backend/nvhttp.cpp

@@ -18,7 +18,8 @@
 #define RESUME_TIMEOUT_MS 30000
 #define QUIT_TIMEOUT_MS 30000
 
-NvHTTP::NvHTTP(NvAddress address, uint16_t httpsPort, QSslCertificate serverCert) :
+NvHTTP::NvHTTP(NvAddress address, uint16_t httpsPort, QSslCertificate serverCert, QNetworkAccessManager* nam) :
+    m_Nam(nam ? nam : new QNetworkAccessManager(this)),
     m_ServerCert(serverCert)
 {
     m_BaseUrlHttp.setScheme("http");
@@ -29,13 +30,11 @@ NvHTTP::NvHTTP(NvAddress address, uint16_t httpsPort, QSslCertificate serverCert
 
     // Never use a proxy server
     QNetworkProxy noProxy(QNetworkProxy::NoProxy);
-    m_Nam.setProxy(noProxy);
-
-    connect(&m_Nam, &QNetworkAccessManager::sslErrors, this, &NvHTTP::handleSslErrors);
+    m_Nam->setProxy(noProxy);
 }
 
-NvHTTP::NvHTTP(NvComputer* computer) :
-    NvHTTP(computer->activeAddress, computer->activeHttpsPort, computer->serverCert)
+NvHTTP::NvHTTP(NvComputer* computer, QNetworkAccessManager* nam) :
+    NvHTTP(computer->activeAddress, computer->activeHttpsPort, computer->serverCert, nam)
 {
 
 }
@@ -492,15 +491,15 @@ NvHTTP::openConnection(QUrl baseUrl,
     request.setAttribute(QNetworkRequest::Http2AllowedAttribute, false);
 #endif
 
-#if QT_VERSION >= QT_VERSION_CHECK(5, 14, 0) && QT_VERSION < QT_VERSION_CHECK(5, 15, 1) && !defined(QT_NO_BEARERMANAGEMENT)
-    // HACK: Set network accessibility to work around QTBUG-80947 (introduced in Qt 5.14.0 and fixed in Qt 5.15.1)
-    QT_WARNING_PUSH
-    QT_WARNING_DISABLE_DEPRECATED
-    m_Nam.setNetworkAccessible(QNetworkAccessManager::Accessible);
-    QT_WARNING_POP
+#if QT_VERSION >= QT_VERSION_CHECK(6, 3, 0)
+    // Use fine-grained idle timeouts to avoid calling QNetworkAccessManager::clearAccessCache(),
+    // which tears down the NAM's global thread each time. We must not keep persistent connections
+    // or GFE will puke.
+    request.setAttribute(QNetworkRequest::ConnectionCacheExpiryTimeoutSecondsAttribute, 0);
 #endif
 
-    QNetworkReply* reply = m_Nam.get(request);
+    auto sslErrorsConnection = connect(m_Nam, &QNetworkAccessManager::sslErrors, this, &NvHTTP::handleSslErrors);
+    QNetworkReply* reply = m_Nam->get(request);
 
     // Run the request with a timeout if requested
     QEventLoop loop;
@@ -523,9 +522,11 @@ NvHTTP::openConnection(QUrl baseUrl,
         reply->abort();
     }
 
-    // We must clear out cached authentication and connections or
-    // GFE will puke next time
-    m_Nam.clearAccessCache();
+#if QT_VERSION < QT_VERSION_CHECK(6, 3, 0)
+    // If we couldn't use fine-grained connection idle timeouts, kill them all now
+    m_Nam->clearAccessCache();
+#endif
+    disconnect(sslErrorsConnection);
 
     // Handle error
     if (reply->error() != QNetworkReply::NoError)

app/backend/nvhttp.h

@@ -109,9 +109,9 @@ public:
         NVLL_VERBOSE
     };
 
-    explicit NvHTTP(NvAddress address, uint16_t httpsPort, QSslCertificate serverCert);
+    explicit NvHTTP(NvAddress address, uint16_t httpsPort, QSslCertificate serverCert, QNetworkAccessManager* nam = nullptr);
 
-    explicit NvHTTP(NvComputer* computer);
+    explicit NvHTTP(NvComputer* computer, QNetworkAccessManager* nam = nullptr);
 
     static
     int
@@ -196,6 +196,6 @@ private:
                    NvLogLevel logLevel);
 
     NvAddress m_Address;
-    QNetworkAccessManager m_Nam;
+    QNetworkAccessManager* m_Nam;
     QSslCertificate m_ServerCert;
 };