Improve lookup speed for QAccessible::uniqueId

When QAccessible::uniqueId was called, it would call QHash::key(),
which has linear time performance. This can cause application
slowdown if a big number of QAccessibleInterface Ids have to be found.

The patch adds an additional QHash to keep track of the inverse
relationship from QAccessibleInterface pointers to their Ids.

Change-Id: I975e3dc0e6c628e2ea701323d8b87184ad133cfb
Task-number: QTBUG-54491
Reviewed-by: Allan Sandfeld Jensen <allan.jensen@qt.io>
Reviewed-by: Frederik Gladhorn <frederik.gladhorn@qt.io>

3 files changed, 12 insertions, 3 deletions

diff --git a/src/gui/accessible/qaccessible.cpp b/src/gui/accessible/qaccessible.cpp
index 4731e8a240..658e0f26ba 100644
--- a/src/gui/accessible/qaccessible.cpp
+++ b/src/gui/accessible/qaccessible.cpp
@@ -755,7 +755,7 @@ void QAccessible::deleteAccessibleInterface(Id id)
 */
 QAccessible::Id QAccessible::uniqueId(QAccessibleInterface *iface)
 {
-    Id id = QAccessibleCache::instance()->idToInterface.key(iface);
+    Id id = QAccessibleCache::instance()->idForInterface(iface);
     if (!id)
         id = registerAccessibleInterface(iface);
     return id;
@@ -768,7 +768,7 @@ QAccessible::Id QAccessible::uniqueId(QAccessibleInterface *iface)
 */
 QAccessibleInterface *QAccessible::accessibleInterface(Id id)
 {
-    return QAccessibleCache::instance()->idToInterface.value(id);
+    return QAccessibleCache::instance()->interfaceForId(id);
 }
 
 
diff --git a/src/gui/accessible/qaccessiblecache.cpp b/src/gui/accessible/qaccessiblecache.cpp
index 0b9366631c..5fae442370 100644
--- a/src/gui/accessible/qaccessiblecache.cpp
+++ b/src/gui/accessible/qaccessiblecache.cpp
@@ -77,6 +77,11 @@ QAccessibleInterface *QAccessibleCache::interfaceForId(QAccessible::Id id) const
     return idToInterface.value(id);
 }
 
+QAccessible::Id QAccessibleCache::idForInterface(QAccessibleInterface *iface) const
+{
+    return interfaceToId.value(iface);
+}
+
 QAccessible::Id QAccessibleCache::insert(QObject *object, QAccessibleInterface *iface) const
 {
     Q_ASSERT(iface);
@@ -84,7 +89,7 @@ QAccessible::Id QAccessibleCache::insert(QObject *object, QAccessibleInterface *
 
     // object might be 0
     Q_ASSERT(!objectToId.contains(object));
-    Q_ASSERT_X(!idToInterface.values().contains(iface), "", "Accessible interface inserted into cache twice!");
+    Q_ASSERT_X(!interfaceToId.contains(iface), "", "Accessible interface inserted into cache twice!");
 
     QAccessible::Id id = acquireId();
     QObject *obj = iface->object();
@@ -94,6 +99,7 @@ QAccessible::Id QAccessibleCache::insert(QObject *object, QAccessibleInterface *
         connect(obj, &QObject::destroyed, this, &QAccessibleCache::objectDestroyed);
     }
     idToInterface.insert(id, iface);
+    interfaceToId.insert(iface, id);
     return id;
 }
 
@@ -109,6 +115,7 @@ void QAccessibleCache::objectDestroyed(QObject* obj)
 void QAccessibleCache::deleteInterface(QAccessible::Id id, QObject *obj)
 {
     QAccessibleInterface *iface = idToInterface.take(id);
+    interfaceToId.take(iface);
     if (!obj)
         obj = iface->object();
     if (obj)
diff --git a/src/gui/accessible/qaccessiblecache_p.h b/src/gui/accessible/qaccessiblecache_p.h
index ffaccbca42..bb33ea2cd4 100644
--- a/src/gui/accessible/qaccessiblecache_p.h
+++ b/src/gui/accessible/qaccessiblecache_p.h
@@ -64,6 +64,7 @@ class Q_GUI_EXPORT QAccessibleCache  :public QObject
 public:
     static QAccessibleCache *instance();
     QAccessibleInterface *interfaceForId(QAccessible::Id id) const;
+    QAccessible::Id idForInterface(QAccessibleInterface *iface) const;
     QAccessible::Id insert(QObject *object, QAccessibleInterface *iface) const;
     void deleteInterface(QAccessible::Id id, QObject *obj = 0);
 
@@ -79,6 +80,7 @@ private:
     QAccessible::Id acquireId() const;
 
     mutable QHash<QAccessible::Id, QAccessibleInterface *> idToInterface;
+    mutable QHash<QAccessibleInterface *, QAccessible::Id> interfaceToId;
     mutable QHash<QObject *, QAccessible::Id> objectToId;
 
 #ifdef Q_OS_MAC