Reduce open and stat system calls for QSettings

The patch moves the global static QSettings object
from QLibrary to QCoreApplication and reduces a
few stat and open calls.

Without the patch, a large Trolltech.conf was
pushed out of the unused settings cache during
startup, meaning Trolltech.conf was parsed
more than once.

Reviewed-by: Liang Qi
(cherry picked from commit 31ef8fa6abc2ea23c6f0a996b36494d88aafb0b5)

4 files changed, 21 insertions, 35 deletions

diff --git a/src/corelib/io/qsettings.cpp b/src/corelib/io/qsettings.cpp
index b084ca5d62..f43fb31856 100644
--- a/src/corelib/io/qsettings.cpp
+++ b/src/corelib/io/qsettings.cpp
@@ -981,23 +981,6 @@ QStringList QSettingsPrivate::splitArgs(const QString &s, int idx)
 // ************************************************************************
 // QConfFileSettingsPrivate
 
-/*
-    If we don't have the permission to read the file, returns false.
-    If the file doesn't exist, returns true.
-*/
-static bool checkAccess(const QString &name)
-{
-    QFileInfo fileInfo(name);
-
-    if (fileInfo.exists()) {
-        QFile file(name);
-        // if the file exists but we can't open it, report an error
-        return file.open(QFile::ReadOnly);
-    } else {
-        return true;
-    }
-}
-
 void QConfFileSettingsPrivate::initFormat()
 {
     extension = (format == QSettings::NativeFormat) ? QLatin1String(".conf") : QLatin1String(".ini");
@@ -1026,18 +1009,13 @@ void QConfFileSettingsPrivate::initFormat()
 
 void QConfFileSettingsPrivate::initAccess()
 {
-    bool readAccess = false;
     if (confFiles[spec]) {
-        readAccess = checkAccess(confFiles[spec]->name);
         if (format > QSettings::IniFormat) {
             if (!readFunc)
-                readAccess = false;
+                setStatus(QSettings::AccessError);
         }
     }
 
-    if (!readAccess)
-        setStatus(QSettings::AccessError);
-
     sync();       // loads the files the first time
 }
 
@@ -1432,7 +1410,7 @@ void QConfFileSettingsPrivate::syncConfFile(int confFileNo)
         We can often optimize the read-only case, if the file on disk
         hasn't changed.
     */
-    if (readOnly) {
+    if (readOnly && confFile->size > 0) {
         QFileInfo fileInfo(confFile->name);
         if (confFile->size == fileInfo.size() && confFile->timeStamp == fileInfo.lastModified())
             return;
@@ -1455,6 +1433,9 @@ void QConfFileSettingsPrivate::syncConfFile(int confFileNo)
     if (!file.isOpen())
         file.open(QFile::ReadOnly);
 
+    if (!createFile && !file.isOpen())
+        setStatus(QSettings::AccessError);
+
 #ifdef Q_OS_WIN
     HANDLE readSemaphore = 0;
     HANDLE writeSemaphore = 0;
diff --git a/src/corelib/kernel/qcoreapplication.cpp b/src/corelib/kernel/qcoreapplication.cpp
index e0841cbadc..2eef70a480 100644
--- a/src/corelib/kernel/qcoreapplication.cpp
+++ b/src/corelib/kernel/qcoreapplication.cpp
@@ -270,6 +270,8 @@ bool QCoreApplicationPrivate::is_app_closing = false;
 Q_CORE_EXPORT bool qt_locale_initialized = false;
 
 
+QSettings *QCoreApplicationPrivate::trolltechConf = 0;
+
 Q_CORE_EXPORT uint qGlobalPostedEventsCount()
 {
     QThreadData *currentThreadData = QThreadData::current();
@@ -371,6 +373,9 @@ QCoreApplicationPrivate::~QCoreApplicationPrivate()
         threadData->postEventList.recursion = 0;
         threadData->quitNow = false;
     }
+
+    delete trolltechConf;
+    trolltechConf = 0;
 }
 
 void QCoreApplicationPrivate::createEventDispatcher()
@@ -692,6 +697,13 @@ void QCoreApplication::init()
     }
 #endif
 
+
+    /*
+      Create an instance of Trolltech.conf. This ensures that the settings will not
+      be thrown out of QSetting's cache for unused settings.
+      */
+    d->trolltechConf = new QSettings(QSettings::UserScope, QLatin1String("Trolltech"));
+
     qt_startup_hook();
 }
 
diff --git a/src/corelib/kernel/qcoreapplication_p.h b/src/corelib/kernel/qcoreapplication_p.h
index fdceab4724..937a101085 100644
--- a/src/corelib/kernel/qcoreapplication_p.h
+++ b/src/corelib/kernel/qcoreapplication_p.h
@@ -55,6 +55,7 @@
 
 #include "QtCore/qcoreapplication.h"
 #include "QtCore/qtranslator.h"
+#include "QtCore/qsettings.h"
 #include "private/qobject_p.h"
 
 #ifdef Q_OS_SYMBIAN
@@ -141,6 +142,7 @@ public:
 #if defined(QT3_SUPPORT)
     static bool useQt3Support;
 #endif
+    static QSettings *trolltechConf;
 };
 
 QT_END_NAMESPACE
diff --git a/src/corelib/plugin/qlibrary.cpp b/src/corelib/plugin/qlibrary.cpp
index 80e927bcc9..6f3ee1c3d3 100644
--- a/src/corelib/plugin/qlibrary.cpp
+++ b/src/corelib/plugin/qlibrary.cpp
@@ -52,6 +52,7 @@
 #include <qmap.h>
 #include <qsettings.h>
 #include <qdatetime.h>
+#include <private/qcoreapplication_p.h>
 #ifdef Q_OS_MAC
 #  include <private/qcore_mac_p.h>
 #endif
@@ -408,12 +409,6 @@ static bool qt_unix_query(const QString &library, uint *version, bool *debug, QB
 typedef QMap<QString, QLibraryPrivate*> LibraryMap;
 
 struct LibraryData {
-    LibraryData() : settings(0) { }
-    ~LibraryData() {
-        delete settings;
-    }
-
-    QSettings *settings;
     LibraryMap libraryMap;
     QSet<QLibraryPrivate*> loadedLibs;
 };
@@ -711,11 +706,7 @@ bool QLibraryPrivate::isPlugin(QSettings *settings)
     QStringList reg;
 #ifndef QT_NO_SETTINGS
     if (!settings) {
-        settings = libraryData()->settings;
-        if (!settings) {
-            settings = new QSettings(QSettings::UserScope, QLatin1String("Trolltech"));
-            libraryData()->settings = settings;
-        }
+        settings = QCoreApplicationPrivate::trolltechConf;
     }
     reg = settings->value(regkey).toStringList();
 #endif