tst_bench_qdiriterator: add benchmark for QDirListing

Make the benchmarks more comparable:
- Store the QDir::Filters in one central var, this way it's the same in
  all the call sites

- Add a `bool forceStat`, when true force calling stat(), either
  explicitly in posix_helper(), or implicitly in Qt classes by e.g.
  calling a QFileInfo method that would have to call system stat()
  internally. Otherwise benchmarking readdir()/dirent showed bigger
  times, which was mostly due to the explicit stat() calls, whereas we
  can use dirent::d_type (on the platforms where it's available)

Drive by change: for std::filesystem::recursive_directory_iterator, set
skip_permission_denied option and use the non-throwing constructor.

Change-Id: Icf138a5dc41d32741c1be611d664b01008b2f3fe
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

tests/benchmarks/corelib/io/qdiriterator/tst_bench_qdiriterator.cpp

@@ -2,6 +2,7 @@
 // SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GPL-3.0-only
 #include <QDebug>
 #include <QDirIterator>
+#include <QDirListing>
 #include <QString>
 #include <qplatformdefs.h>
 
@@ -23,16 +24,30 @@
 #include <filesystem>
 #endif
 
+using namespace Qt::StringLiterals;
+
+constexpr bool forceStat = false;
+
 class tst_QDirIterator : public QObject
 {
     Q_OBJECT
 
     void data();
+
+    const QDir::Filters dirFilters =
+            // QDir::AllEntries | QDir::Hidden | QDir::NoDotAndDotDot
+            QDir::AllEntries | QDir::Hidden
+            //QDir::Files | QDir::NoDotAndDotDot,
+            // QDir::Files,
+            ;
+
 private slots:
     void posix();
     void posix_data() { data(); }
     void diriterator();
     void diriterator_data() { data(); }
+    void dirlisting();
+    void dirlisting_data() { data(); }
     void fsiterator();
     void fsiterator_data() { data(); }
     void stdRecursiveDirectoryIterator();
@@ -118,9 +133,20 @@ static int posix_helper(const char *dirpath)
         QByteArray ba = dirpath;
         ba += '/';
         ba += entry->d_name;
+        bool isDir = false;
+#if defined(_DIRENT_HAVE_D_TYPE) || defined(Q_OS_BSD4)
+        isDir = entry->d_type == DT_DIR;
+        if (forceStat) {
             QT_STATBUF st;
             QT_LSTAT(ba.constData(), &st);
-        if (S_ISDIR(st.st_mode))
+        }
+#else // d_type not available >>> must stat() to see if it's a dir
+        QT_STATBUF st;
+        QT_LSTAT(ba.constData(), &st);
+        isDir = S_ISDIR(st.st_mode);
+#endif
+
+        if (isDir)
             count += posix_helper(ba.constData());
     }
 
@@ -157,14 +183,12 @@ void tst_QDirIterator::diriterator()
     QBENCHMARK {
         int c = 0;
 
-        QDirIterator dir(dirpath,
-            //QDir::AllEntries | QDir::Hidden | QDir::NoDotAndDotDot,
-            //QDir::AllEntries | QDir::Hidden,
-            QDir::Files,
-            QDirIterator::Subdirectories);
+        QDirIterator dir(dirpath, dirFilters, QDirIterator::Subdirectories);
 
         while (dir.hasNext()) {
             const auto fi = dir.nextFileInfo();
+            if (forceStat)
+                fi.size();
             //printf("%s\n", qPrintable(dir.fileName()));
             0 && printf("%d %s\n",
                 fi.isDir(),
@@ -178,6 +202,28 @@ void tst_QDirIterator::diriterator()
     qDebug() << count;
 }
 
+void tst_QDirIterator::dirlisting()
+{
+    QFETCH(QByteArray, dirpath);
+
+    int count = 0;
+
+    QBENCHMARK {
+        int c = 0;
+
+        QDirListing dir(dirpath, dirFilters, QDirListing::IteratorFlag::Recursive);
+
+        for (const auto &dirEntry : dir) {
+            const auto path = dirEntry.filePath();
+            if (forceStat)
+                dirEntry.size();
+            ++c;
+        }
+        count = c;
+    }
+    qDebug() << count;
+}
+
 void tst_QDirIterator::fsiterator()
 {
     QFETCH(QByteArray, dirpath);
@@ -189,14 +235,12 @@ void tst_QDirIterator::fsiterator()
         int c = 0;
 
         dump && printf("\n\n\n\n");
-        QDirIteratorTest::QFileSystemIterator dir(dirpath,
-            //QDir::AllEntries | QDir::Hidden | QDir::NoDotAndDotDot,
-            //QDir::AllEntries | QDir::Hidden,
-            //QDir::Files | QDir::NoDotAndDotDot,
-            QDir::Files,
-            QDirIteratorTest::QFileSystemIterator::Subdirectories);
+        QDirIteratorTest::QFileSystemIterator dir(
+            dirpath, dirFilters, QDirIteratorTest::QFileSystemIterator::Subdirectories);
 
         for (; !dir.atEnd(); dir.next()) {
+            if (forceStat)
+                dir.fileInfo().size();
             dump && printf("%d %s\n",
                 dir.fileInfo().isDir(),
                 //qPrintable(dir.fileInfo().absoluteFilePath()),
@@ -217,10 +261,17 @@ void tst_QDirIterator::stdRecursiveDirectoryIterator()
 
     int count = 0;
 
+    namespace fs = std::filesystem;
+    std::error_code ec;
+
+    // Note that fs::recursive_directory_iterator may be calling stat() internally,
+    // that depends on the implementation. So the benchmark times might "seem" higher
+    // than the other methods in this source file.
     QBENCHMARK {
         int c = 0;
-        for (auto obj : std::filesystem::recursive_directory_iterator(dirpath.data())) {
-            if (obj.is_directory())
+        for (const auto &dirEntry : fs::recursive_directory_iterator(
+                                dirpath.data(), fs::directory_options::skip_permission_denied, ec)) {
+            if (dirEntry.is_directory())
                 continue;
             c++;
         }