Speed up sorting of dir entries when sorted by date

QDateTime will attempt to convert unknown types of date to UTC time, which isn't
exactly a fast process. As we don't care about local timezones in the process of
sorting (as this is purely for ordering, not display to the end user), we can
force the dates to use UTC time, avoiding the unnecessary local timezone lookup.

This also adds a benchmark covering this case.

Benchmark results, Qt 5:
 - before: 11, 489ms
 - after: 273ms

Qt 4.8:
 - before: 20, 848ms
 - after: 278ms

Change-Id: I87fa6260e820b5b172d3306ff395dafe767c33ff
Reported-by: Thomas Perl <m@thp.io>
Reviewed-by: Alberto Mardegan <mardy@users.sourceforge.net>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

diff --git a/src/corelib/io/qdir.cpp b/src/corelib/io/qdir.cpp
index 59b93f1..2753d63 100644 (file)
--- a/src/corelib/io/qdir.cpp
+++ b/src/corelib/io/qdir.cpp
@@ -232,9 +232,20 @@ bool QDirSortItemComparator::operator()(const QDirSortItem &n1, const QDirSortIt
                  | (qt_cmp_si_sort_flags & QDir::Type);
 
     switch (sortBy) {
-      case QDir::Time:
-        r = f1->item.lastModified().secsTo(f2->item.lastModified());
+      case QDir::Time: {
+        QDateTime firstModified = f1->item.lastModified();
+        QDateTime secondModified = f2->item.lastModified();
+
+        // QDateTime by default will do all sorts of conversions on these to
+        // find timezones, which is incredibly expensive. As we aren't
+        // presenting these to the user, we don't care (at all) about the
+        // local timezone, so force them to UTC to avoid that conversion.
+        firstModified.setTimeSpec(Qt::UTC);
+        secondModified.setTimeSpec(Qt::UTC);
+
+        r = firstModified.secsTo(secondModified);
         break;
+      }
       case QDir::Size:
           r = int(qBound<qint64>(-1, f2->item.size() - f1->item.size(), 1));
         break;

diff --git a/tests/benchmarks/corelib/io/qdir/10000/bench_qdir_10000.cpp b/tests/benchmarks/corelib/io/qdir/10000/bench_qdir_10000.cpp
index 2de98ef..d741ae7 100644 (file)
--- a/tests/benchmarks/corelib/io/qdir/10000/bench_qdir_10000.cpp
+++ b/tests/benchmarks/corelib/io/qdir/10000/bench_qdir_10000.cpp
@@ -155,6 +155,18 @@ private slots:
         }
     }
 
+    void sorted_byTime() {
+        QDir testdir(QDir::tempPath() + QLatin1String("/test_speed"));
+        testdir.setSorting(QDir::Time);
+        testdir.setFilter(QDir::AllEntries | QDir::System | QDir::Hidden);
+        QBENCHMARK {
+            QStringList fileList = testdir.entryList(QDir::NoFilter, QDir::Time);
+            foreach (const QString &filename, fileList) {
+
+            }
+        }
+    }
+
     void sizeSpeedWithoutFilterLowLevel() {
         QDir testdir(QDir::tempPath() + QLatin1String("/test_speed"));
 #ifdef Q_OS_WIN