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Stop unloading plugins in QPluginLoader and QFactoryLoader

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QPluginLoader hasn't unloaded in its destructor since Qt 5.0, but we
missed the equivalent code in QFactoryLoader (which bypasses
QPluginLoader). Besides, QPluginLoader::unload() was still doing
unloading, which it won't anymore.

Not unloading plugins is Qt's policy, as decided during the 5.0
development process and reaffirmed now in 5.6. This is due to static
data in plugins leaking out and remaining in use past the unloading of
the plugin, causing crashes.

This does not affect QLibrary and QLibrary::unload(). Those are meant
for non-Qt loadable modules, so unloading them may be safe.

Task-number: QTBUG-49061
Discussed-on: http://lists.qt-project.org/pipermail/development/2015-November/023681.html
Change-Id: I461e9fc7199748faa187ffff1416070f138df8db
(cherry picked from commit 494376f980)
Discussed-again-on: http://lists.qt-project.org/pipermail/development/2016-October/027476.html
Reviewed-by: Lars Knoll <lars.knoll@qt.io>
This commit is contained in:
Thiago Macieira 2015-11-12 10:14:51 -08:00
parent 5f6c0418fe
commit ca4d93d85e
2 changed files with 7 additions and 4 deletions
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6
src/corelib/plugin/qfactoryloader.cpp
View File

@ -208,10 +208,12 @@ void QFactoryLoader::update()
++keyUsageCount;
}
}
if (keyUsageCount || keys.isEmpty())
if (keyUsageCount || keys.isEmpty()) {
library->setLoadHints(QLibrary::PreventUnloadHint); // once loaded, don't unload
d->libraryList += library;
else
} else {
library->release();
}
}
}
#else

5
src/corelib/plugin/qpluginloader.cpp
View File

@ -148,6 +148,7 @@ QPluginLoader::QPluginLoader(const QString &fileName, QObject *parent)
: QObject(parent), d(0), did_load(false)
{
setFileName(fileName);
setLoadHints(QLibrary::PreventUnloadHint);
}
/*!
@ -342,7 +343,7 @@ static QString locatePlugin(const QString& fileName)
void QPluginLoader::setFileName(const QString &fileName)
{
#if defined(QT_SHARED)
QLibrary::LoadHints lh;
QLibrary::LoadHints lh = QLibrary::PreventUnloadHint;
if (d) {
lh = d->loadHints();
d->release();
@ -391,7 +392,7 @@ Q_GLOBAL_STATIC(StaticPluginList, staticPluginList)
\brief Give the load() function some hints on how it should behave.
You can give hints on how the symbols in the plugin are
resolved. By default, none of the hints are set.
resolved. By default since Qt 5.7, QLibrary::PreventUnloadHint is set.
See the documentation of QLibrary::loadHints for a complete
description of how this property works.