Fix race condition for client buffer integration initialization

This race happened because QWaylandIntegration::clientBufferIntegration (which
lazily initializes the integration) was called from numerous places including
code that may run on different threads without any kind of syncrhonization.

An example of this is Qt3D, which indirectly and simultaneously calls
createPlatformWindow (from the GUI thread) and createPlatformOpenGLContext
(from its render thread), both of which needs to use the client buffer
integration.

In this patch, we fix it by first checking if the integration is initialized.
In that case, it's safe to use it. Otherwise we lock a mutex, re-check if
initialization has happened on another thread in the meantime, and then finally
we initialize it.

This way we should avoid the expense of mutex locking after initialization is
complete, while still staying race free during initialization.

Fixes: QTBUG-76504
Change-Id: I327840ebf41e014882cb659bc3e4fafb7bdb7a98
Reviewed-by: David Edmundson <davidedmundson@kde.org>
Reviewed-by: Paul Olav Tvete <paul.tvete@qt.io>
This commit is contained in:
Johan Klokkhammer Helsing 2019-07-08 10:22:03 +02:00
parent ec510cb38c
commit 8b50d2c6cc
2 changed files with 22 additions and 11 deletions

View File

@ -301,11 +301,14 @@ QPlatformTheme *QWaylandIntegration::createPlatformTheme(const QString &name) co
return GenericWaylandTheme::createUnixTheme(name); return GenericWaylandTheme::createUnixTheme(name);
} }
// May be called from non-GUI threads
QWaylandClientBufferIntegration *QWaylandIntegration::clientBufferIntegration() const QWaylandClientBufferIntegration *QWaylandIntegration::clientBufferIntegration() const
{ {
if (!mClientBufferIntegrationInitialized) // Do an inexpensive check first to avoid locking whenever possible
if (Q_UNLIKELY(!mClientBufferIntegrationInitialized))
const_cast<QWaylandIntegration *>(this)->initializeClientBufferIntegration(); const_cast<QWaylandIntegration *>(this)->initializeClientBufferIntegration();
Q_ASSERT(mClientBufferIntegrationInitialized);
return mClientBufferIntegration && mClientBufferIntegration->isValid() ? mClientBufferIntegration.data() : nullptr; return mClientBufferIntegration && mClientBufferIntegration->isValid() ? mClientBufferIntegration.data() : nullptr;
} }
@ -325,9 +328,12 @@ QWaylandShellIntegration *QWaylandIntegration::shellIntegration() const
return mShellIntegration.data(); return mShellIntegration.data();
} }
// May be called from non-GUI threads
void QWaylandIntegration::initializeClientBufferIntegration() void QWaylandIntegration::initializeClientBufferIntegration()
{ {
mClientBufferIntegrationInitialized = true; QMutexLocker lock(&mClientBufferInitLock);
if (mClientBufferIntegrationInitialized)
return;
QString targetKey; QString targetKey;
bool disableHardwareIntegration = qEnvironmentVariableIsSet("QT_WAYLAND_DISABLE_HW_INTEGRATION"); bool disableHardwareIntegration = qEnvironmentVariableIsSet("QT_WAYLAND_DISABLE_HW_INTEGRATION");
@ -345,17 +351,20 @@ void QWaylandIntegration::initializeClientBufferIntegration()
if (targetKey.isEmpty()) { if (targetKey.isEmpty()) {
qWarning("Failed to determine what client buffer integration to use"); qWarning("Failed to determine what client buffer integration to use");
return; } else {
QStringList keys = QWaylandClientBufferIntegrationFactory::keys();
if (keys.contains(targetKey)) {
mClientBufferIntegration.reset(QWaylandClientBufferIntegrationFactory::create(targetKey, QStringList()));
}
if (mClientBufferIntegration)
mClientBufferIntegration->initialize(mDisplay.data());
else
qWarning("Failed to load client buffer integration: %s\n", qPrintable(targetKey));
} }
QStringList keys = QWaylandClientBufferIntegrationFactory::keys(); // This must be set last to make sure other threads don't use the
if (keys.contains(targetKey)) { // integration before initialization is complete.
mClientBufferIntegration.reset(QWaylandClientBufferIntegrationFactory::create(targetKey, QStringList())); mClientBufferIntegrationInitialized = true;
}
if (mClientBufferIntegration)
mClientBufferIntegration->initialize(mDisplay.data());
else
qWarning("Failed to load client buffer integration: %s\n", qPrintable(targetKey));
} }
void QWaylandIntegration::initializeServerBufferIntegration() void QWaylandIntegration::initializeServerBufferIntegration()

View File

@ -54,6 +54,7 @@
#include <QtWaylandClient/qtwaylandclientglobal.h> #include <QtWaylandClient/qtwaylandclientglobal.h>
#include <qpa/qplatformintegration.h> #include <qpa/qplatformintegration.h>
#include <QtCore/QScopedPointer> #include <QtCore/QScopedPointer>
#include <QtCore/QMutex>
QT_BEGIN_NAMESPACE QT_BEGIN_NAMESPACE
@ -148,6 +149,7 @@ private:
QScopedPointer<QPlatformAccessibility> mAccessibility; QScopedPointer<QPlatformAccessibility> mAccessibility;
#endif #endif
bool mFailed = false; bool mFailed = false;
QMutex mClientBufferInitLock;
bool mClientBufferIntegrationInitialized = false; bool mClientBufferIntegrationInitialized = false;
bool mServerBufferIntegrationInitialized = false; bool mServerBufferIntegrationInitialized = false;
bool mShellIntegrationInitialized = false; bool mShellIntegrationInitialized = false;