Windows: optimize BTLE device discovery

Previously we were doing full service discovery every time when the
BluetoothLEAdvertisementWatcher reports a new advertisement.
This results in a very high CPU usage during BTLE device discovery
on some configurations.

In practice such approach might not be needed, because most BTLE
devices repeatedly advertise the same data.

With this patch we do a detailed service discovery only when a new
device is added, or when the list of advertised services has changed.
Note that we still need to handle all the incoming advertisements,
because we want to report changes in other parameters, such as RSSI.

Fixes: QTBUG-111116
Pick-to: 6.5 6.5.0 6.2
Change-Id: I0863739a2fb21d04e9a728adc68e3f197f1966e3
Reviewed-by: Juha Vuolle <juha.vuolle@qt.io>
Reviewed-by: Oliver Wolff <oliver.wolff@qt.io>

1 files changed, 22 insertions, 19 deletions

diff --git a/src/bluetooth/qbluetoothdevicediscoveryagent_winrt.cpp b/src/bluetooth/qbluetoothdevicediscoveryagent_winrt.cpp
index e0d3111a..48929d35 100644
--- a/src/bluetooth/qbluetoothdevicediscoveryagent_winrt.cpp
+++ b/src/bluetooth/qbluetoothdevicediscoveryagent_winrt.cpp
@@ -406,6 +406,7 @@ void QWinRTBluetoothDeviceDiscoveryWorker::onAdvertisementDataReceived(
         const ServiceData &serviceData, const QList<QBluetoothUuid> &uuids)
 {
     // Merge newly found services with list of currently found ones
+    bool needDiscoverServices = false;
     {
         QMutexLocker locker(&m_leDevicesMutex);
         if (m_foundLEDevicesMap.contains(address)) {
@@ -426,14 +427,13 @@ void QWinRTBluetoothDeviceDiscoveryWorker::onAdvertisementDataReceived(
                 if (adInfo.serviceData != m_foundLEDevicesMap[address].serviceData)
                     changedFields.setFlag((QBluetoothDeviceInfo::Field::ServiceData));
             }
-            bool newServiceAdded = false;
             for (const QBluetoothUuid &uuid : std::as_const(uuids)) {
                 if (!foundServices.contains(uuid)) {
                     foundServices.append(uuid);
-                    newServiceAdded = true;
+                    needDiscoverServices = true;
                 }
             }
-            if (!newServiceAdded) {
+            if (!needDiscoverServices) {
                 if (!changedFields.testFlag(QBluetoothDeviceInfo::Field::None)) {
                     QMetaObject::invokeMethod(this, "deviceDataChanged", Qt::AutoConnection,
                                               Q_ARG(QBluetoothAddress, QBluetoothAddress(address)),
@@ -445,6 +445,7 @@ void QWinRTBluetoothDeviceDiscoveryWorker::onAdvertisementDataReceived(
             }
             m_foundLEDevicesMap[address].services = foundServices;
         } else {
+            needDiscoverServices = true;
             LEAdvertisingInfo info;
             info.services = std::move(uuids);
             info.manufacturerData = std::move(manufacturerData);
@@ -453,24 +454,26 @@ void QWinRTBluetoothDeviceDiscoveryWorker::onAdvertisementDataReceived(
             m_foundLEDevicesMap.insert(address, info);
         }
     }
-    ++m_pendingDevices; // as if we discovered a new LE device
-    auto thisPtr = shared_from_this();
-    auto asyncOp = BluetoothLEDevice::FromBluetoothAddressAsync(address);
-    asyncOp.Completed([thisPtr, address](auto &&op, AsyncStatus status) {
-        if (thisPtr) {
-            if (status == AsyncStatus::Completed) {
-                BluetoothLEDevice device = op.GetResults();
-                if (device) {
-                    thisPtr->handleLowEnergyDevice(device);
-                    return;
+    if (needDiscoverServices) {
+        ++m_pendingDevices; // as if we discovered a new LE device
+        auto thisPtr = shared_from_this();
+        auto asyncOp = BluetoothLEDevice::FromBluetoothAddressAsync(address);
+        asyncOp.Completed([thisPtr, address](auto &&op, AsyncStatus status) {
+            if (thisPtr) {
+                if (status == AsyncStatus::Completed) {
+                    BluetoothLEDevice device = op.GetResults();
+                    if (device) {
+                        thisPtr->handleLowEnergyDevice(device);
+                        return;
+                    }
                 }
+                // status != Completed or failed to extract result
+                qCDebug(QT_BT_WINDOWS) << "Failed to get LE device from address"
+                                       << QBluetoothAddress(address);
+                invokeDecrementPendingDevicesCountAndCheckFinished(thisPtr);
             }
-            // status != Completed or failed to extract result
-            qCDebug(QT_BT_WINDOWS) << "Failed to get LE device from address"
-                                   << QBluetoothAddress(address);
-            invokeDecrementPendingDevicesCountAndCheckFinished(thisPtr);
-        }
-    });
+        });
+    }
 }
 
 void QWinRTBluetoothDeviceDiscoveryWorker::stopAdvertisementWatcher()