Prefer QHash over QMap for faster key lookup

amortized O(1) for QHash VS. stable O(log n) for QMap
+ optimize usage cases by decreasing the amount of key lookups

Change-Id: I169b2d97f07854ce5aca030321820a866d0038ed
Reviewed-by: Maurice Kalinowski <maurice.kalinowski@qt.io>

2 files changed, 28 insertions, 19 deletions

diff --git a/src/mqtt/qmqttconnection.cpp b/src/mqtt/qmqttconnection.cpp
index 61a6ef0..bbad0bd 100644
--- a/src/mqtt/qmqttconnection.cpp
+++ b/src/mqtt/qmqttconnection.cpp
@@ -466,15 +466,22 @@ QMqttSubscription *QMqttConnection::sendControlSubscribe(const QMqttTopicFilter
     qCDebug(lcMqttConnection) << Q_FUNC_INFO << " Topic:" << topic << " qos:" << qos;
 
     if (m_clientPrivate->m_protocolVersion == QMqttClient::MQTT_5_0) {
-        if (!topic.sharedSubscriptionName().isEmpty()) {
+        const QString sharedSubscriptionName = topic.sharedSubscriptionName();
+        if (!sharedSubscriptionName.isEmpty()) {
             const QMqttTopicFilter filter(topic.filter().section(QLatin1Char('/'), 2));
-            if (m_activeSubscriptions.contains(filter)
-                    && m_activeSubscriptions.value(filter)->sharedSubscriptionName() == topic.sharedSubscriptionName())
-                return m_activeSubscriptions[filter];
-        } else if (m_activeSubscriptions.contains(topic) && !m_activeSubscriptions.value(topic)->isSharedSubscription())
-            return m_activeSubscriptions[topic];
-    } else if (m_activeSubscriptions.contains(topic))
-        return m_activeSubscriptions[topic];
+            auto it = m_activeSubscriptions.constFind(filter);
+            if (it != m_activeSubscriptions.cend() && (*it)->sharedSubscriptionName() == sharedSubscriptionName)
+                return *it;
+        } else {
+            auto it = m_activeSubscriptions.constFind(topic);
+            if (it != m_activeSubscriptions.cend() && !(*it)->isSharedSubscription())
+                return *it;
+        }
+    } else {
+        auto it = m_activeSubscriptions.constFind(topic);
+        if (it != m_activeSubscriptions.cend())
+            return *it;
+    }
 
     // has to have 0010 as bits 3-0, maybe update SUBSCRIBE instead?
     // MQTT-3.8.1-1
@@ -1451,13 +1458,13 @@ void QMqttConnection::finalize_connack()
 void QMqttConnection::finalize_suback()
 {
     const quint16 id = readBufferTyped<quint16>(&m_missingData);
-    if (!m_pendingSubscriptionAck.contains(id)) {
+
+    auto sub = m_pendingSubscriptionAck.take(id);
+    if (Q_UNLIKELY(sub == nullptr)) {
         qCDebug(lcMqttConnection) << "Received SUBACK for unknown subscription request.";
         return;
     }
 
-    auto sub = m_pendingSubscriptionAck.take(id);
-
     if (m_clientPrivate->m_protocolVersion == QMqttClient::MQTT_5_0)
         readSubscriptionProperties(sub);
 
@@ -1485,11 +1492,13 @@ void QMqttConnection::finalize_unsuback()
 {
     const quint16 id = readBufferTyped<quint16>(&m_missingData);
     qCDebug(lcMqttConnectionVerbose) << "Finalize UNSUBACK: " << id;
-    if (!m_pendingUnsubscriptions.contains(id)) {
+
+    auto sub = m_pendingUnsubscriptions.take(id);
+    if (Q_UNLIKELY(sub == nullptr)) {
         qCDebug(lcMqttConnection) << "Received UNSUBACK for unknown request.";
         return;
     }
-    auto sub = m_pendingUnsubscriptions.take(id);
+
     sub->setState(QMqttSubscription::Unsubscribed);
     m_activeSubscriptions.remove(sub->topic());
 }
diff --git a/src/mqtt/qmqttconnection_p.h b/src/mqtt/qmqttconnection_p.h
index 84dc875..e8ecfde 100644
--- a/src/mqtt/qmqttconnection_p.h
+++ b/src/mqtt/qmqttconnection_p.h
@@ -46,7 +46,7 @@
 #include "qmqttmessage.h"
 #include "qmqttsubscription.h"
 #include <QtCore/QBuffer>
-#include <QtCore/QMap>
+#include <QtCore/QHash>
 #include <QtCore/QObject>
 #include <QtCore/QSharedPointer>
 #include <QtCore/QTimer>
@@ -147,11 +147,11 @@ private:
     QMqttControlPacket::PacketType m_currentPacket{QMqttControlPacket::UNKNOWN};
 
     bool writePacketToTransport(const QMqttControlPacket &p);
-    QMap<quint16, QMqttSubscription *> m_pendingSubscriptionAck;
-    QMap<quint16, QMqttSubscription *> m_pendingUnsubscriptions;
-    QMap<QMqttTopicFilter, QMqttSubscription *> m_activeSubscriptions;
-    QMap<quint16, QSharedPointer<QMqttControlPacket>> m_pendingMessages;
-    QMap<quint16, QSharedPointer<QMqttControlPacket>> m_pendingReleaseMessages;
+    QHash<quint16, QMqttSubscription *> m_pendingSubscriptionAck;
+    QHash<quint16, QMqttSubscription *> m_pendingUnsubscriptions;
+    QHash<QMqttTopicFilter, QMqttSubscription *> m_activeSubscriptions;
+    QHash<quint16, QSharedPointer<QMqttControlPacket>> m_pendingMessages;
+    QHash<quint16, QSharedPointer<QMqttControlPacket>> m_pendingReleaseMessages;
     InternalConnectionState m_internalState{BrokerDisconnected};
     QTimer m_pingTimer;