QFileSystemWatcherEngines: port some Java-style iterators to ranged-for

Java-style iterators are scheduled to be deprecated.

The general pattern used in the patch is that instead of copying an
input list, then iterating over the copy with some calls to
it.remove() (which leads to quadratic-complexity loops), we simply
copy conditionally (a la remove_copy_if instead of remove_if).

To make clearer what's going on, rename the outgoing list to
'unhandled'.

To avoid having to touch too much of the loops' structure, which
sometimes is quite convoluted, use qScopeGuard to do the append to
'unhandled', unless the original code removed the element.

Saves a surprising almost 5KiB in text size on GCC 9.1 optimized
AMD64 Linux builds.

Change-Id: Ifd861de9aa48d66b420858606998dd08a8401e03
Reviewed-by: Giuseppe D'Angelo <giuseppe.dangelo@kdab.com>
 
 
 
 
 
 
 

1 files changed, 11 insertions, 13 deletions

diff --git a/src/corelib/io/qfilesystemwatcher_polling.cpp b/src/corelib/io/qfilesystemwatcher_polling.cpp
index 903c15f4a9..a95a48cc8f 100644
--- a/src/corelib/io/qfilesystemwatcher_polling.cpp
+++ b/src/corelib/io/qfilesystemwatcher_polling.cpp
@@ -38,6 +38,7 @@
 ****************************************************************************/
 
 #include "qfilesystemwatcher_polling_p.h"
+#include <QtCore/qscopeguard.h>
 #include <QtCore/qtimer.h>
 
 QT_BEGIN_NAMESPACE
@@ -53,10 +54,9 @@ QStringList QPollingFileSystemWatcherEngine::addPaths(const QStringList &paths,
                                                       QStringList *files,
                                                       QStringList *directories)
 {
-    QStringList p = paths;
-    QMutableListIterator<QString> it(p);
-    while (it.hasNext()) {
-        QString path = it.next();
+    QStringList unhandled;
+    for (const QString &path : paths) {
+        auto sg = qScopeGuard([&]{ unhandled.push_back(path); });
         QFileInfo fi(path);
         if (!fi.exists())
             continue;
@@ -73,7 +73,7 @@ QStringList QPollingFileSystemWatcherEngine::addPaths(const QStringList &paths,
             files->append(path);
             this->files.insert(path, fi);
         }
-        it.remove();
+        sg.dismiss();
     }
 
     if ((!this->files.isEmpty() ||
@@ -82,23 +82,21 @@ QStringList QPollingFileSystemWatcherEngine::addPaths(const QStringList &paths,
         timer.start(PollingInterval);
     }
 
-    return p;
+    return unhandled;
 }
 
 QStringList QPollingFileSystemWatcherEngine::removePaths(const QStringList &paths,
                                                          QStringList *files,
                                                          QStringList *directories)
 {
-    QStringList p = paths;
-    QMutableListIterator<QString> it(p);
-    while (it.hasNext()) {
-        QString path = it.next();
+    QStringList unhandled;
+    for (const QString &path : paths) {
         if (this->directories.remove(path)) {
             directories->removeAll(path);
-            it.remove();
         } else if (this->files.remove(path)) {
             files->removeAll(path);
-            it.remove();
+        } else {
+            unhandled.push_back(path);
         }
     }
 
@@ -107,7 +105,7 @@ QStringList QPollingFileSystemWatcherEngine::removePaths(const QStringList &path
         timer.stop();
     }
 
-    return p;
+    return unhandled;
 }
 
 void QPollingFileSystemWatcherEngine::timeout()