From 3e6b42ae9dbf4f90ba890d78a4c49f9936f4976b Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?M=C3=A5rten=20Nordheim?= <marten.nordheim@qt.io>
Date: Fri, 27 Aug 2021 16:48:21 +0200
Subject: [PATCH] compressEvents: limit iteration

Slightly improves performance in the new benchmark

Change-Id: I2d71143ff7bc1f32ebb172f20be1843dec123e6c
Reviewed-by: Allan Sandfeld Jensen <allan.jensen@qt.io>
---
 src/corelib/kernel/qcoreapplication.cpp       | 18 ++++++++-----
 .../tst_bench_qcoreapplication.cpp            | 26 +++++++++++++++++++
 2 files changed, 38 insertions(+), 6 deletions(-)

diff --git a/src/corelib/kernel/qcoreapplication.cpp b/src/corelib/kernel/qcoreapplication.cpp
index 88f855a89e6..60f956faed4 100644
--- a/src/corelib/kernel/qcoreapplication.cpp
+++ b/src/corelib/kernel/qcoreapplication.cpp
@@ -1729,15 +1729,21 @@ bool QCoreApplication::compressEvent(QEvent *event, QObject *receiver, QPostEven
     Q_ASSERT(receiver);
     Q_ASSERT(postedEvents);
 
+    auto receiverPostedEvents = receiver->d_func()->postedEvents;
     // compress posted timers to this object.
-    if (event->type() == QEvent::Timer && receiver->d_func()->postedEvents > 0) {
-        int timerId = ((QTimerEvent *) event)->timerId();
-        for (const QPostEvent &e : std::as_const(*postedEvents)) {
-            if (e.receiver == receiver && e.event && e.event->type() == QEvent::Timer
-                && ((QTimerEvent *) e.event)->timerId() == timerId) {
+    if (event->type() == QEvent::Timer && receiverPostedEvents > 0) {
+        int timerId = static_cast<QTimerEvent *>(event)->timerId();
+        auto sameReceiver = [receiver](const QPostEvent &e) { return e.receiver == receiver; };
+        auto it = std::find_if(postedEvents->cbegin(), postedEvents->cend(), sameReceiver);
+        while (receiverPostedEvents > 0 && it != postedEvents->cend()) {
+            if (it->event && it->event->type() == QEvent::Timer
+                && static_cast<QTimerEvent *>(it->event)->timerId() == timerId) {
                 delete event;
                 return true;
             }
+
+            if (--receiverPostedEvents)
+                it = std::find_if(it + 1, postedEvents->cend(), sameReceiver);
         }
         return false;
     }
@@ -1753,7 +1759,7 @@ bool QCoreApplication::compressEvent(QEvent *event, QObject *receiver, QPostEven
         return false;
     }
 
-    if (event->type() == QEvent::Quit && receiver->d_func()->postedEvents > 0) {
+    if (event->type() == QEvent::Quit && receiverPostedEvents > 0) {
         for (const QPostEvent &cur : std::as_const(*postedEvents)) {
             if (cur.receiver != receiver
                     || cur.event == nullptr
diff --git a/tests/benchmarks/corelib/kernel/qcoreapplication/tst_bench_qcoreapplication.cpp b/tests/benchmarks/corelib/kernel/qcoreapplication/tst_bench_qcoreapplication.cpp
index 044acee3667..640ee0c0e45 100644
--- a/tests/benchmarks/corelib/kernel/qcoreapplication/tst_bench_qcoreapplication.cpp
+++ b/tests/benchmarks/corelib/kernel/qcoreapplication/tst_bench_qcoreapplication.cpp
@@ -10,6 +10,9 @@ Q_OBJECT
 private slots:
     void event_posting_benchmark_data();
     void event_posting_benchmark();
+
+    void event_posting_multiple_objects_benchmark_data();
+    void event_posting_multiple_objects_benchmark();
 };
 
 void tst_QCoreApplication::event_posting_benchmark_data()
@@ -39,6 +42,29 @@ void tst_QCoreApplication::event_posting_benchmark()
     }
 }
 
+void tst_QCoreApplication::event_posting_multiple_objects_benchmark_data()
+{
+    event_posting_benchmark_data();
+}
+
+void tst_QCoreApplication::event_posting_multiple_objects_benchmark()
+{
+    QFETCH(int, size);
+
+    QObject objects[15]; // The size of the array has not been chosen through any meaningful means
+
+    QRandomGenerator gen;
+
+    // benchmark posting & sending events
+    QBENCHMARK {
+        for (int i = 0; i < size; ++i) {
+            QCoreApplication::postEvent(&objects[gen.bounded(0, int(std::size(objects)))],
+                                        new QTimerEvent(i % 10));
+        }
+        QCoreApplication::sendPostedEvents();
+    }
+}
+
 QTEST_MAIN(tst_QCoreApplication)
 
 #include "tst_bench_qcoreapplication.moc"