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Partially revert "Windows: stop using _beginthreadex on regular builds"

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This pertially reverts commit 3ec57107ce
and brings back the hack to prevent the DLL from being unloaded. It
should have been enough, but we've got reports that it's still causing
trouble. Since it causes not much harm to keep the DLL loaded (worst
case scenario is that QtDBus and QtCore remain loaded after a plugin
gets unloaded), we'll keep it.

Note: Microsoft is aware that their way of killing threads on process
exit is a flaw. See https://blogs.msdn.microsoft.com/oldnewthing/20070502-00/?p=27023/

Task-number: QTBUG-53031
Change-Id: I2962773739e34633b033fffd1493dce695b008c0
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@qt.io>
Reviewed-by: Maurice Kalinowski <maurice.kalinowski@qt.io>
This commit is contained in:
Thiago Macieira 2016-12-26 14:23:39 -02:00
parent e2ab932276
commit 9449325f2b
1 changed files with 35 additions and 0 deletions
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35
src/dbus/qdbusconnection.cpp
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@ -69,6 +69,10 @@
QT_BEGIN_NAMESPACE
#ifdef Q_OS_WIN
static void preventDllUnload();
#endif
Q_GLOBAL_STATIC(QDBusConnectionManager, _q_manager)
struct QDBusConnectionManager::ConnectionRequestData
@ -139,6 +143,10 @@ QDBusConnectionManager::QDBusConnectionManager()
this, &QDBusConnectionManager::createServer, Qt::BlockingQueuedConnection);
moveToThread(this); // ugly, don't do this in other projects
#ifdef Q_OS_WIN
// prevent the library from being unloaded on Windows. See comments in the function.
preventDllUnload();
#endif
defaultBuses[0] = defaultBuses[1] = Q_NULLPTR;
start();
}
@ -1262,4 +1270,31 @@ QByteArray QDBusConnection::localMachineId()
QT_END_NAMESPACE
#ifdef Q_OS_WIN
# include <qt_windows.h>
QT_BEGIN_NAMESPACE
static void preventDllUnload()
{
// Thread termination is really wacky on Windows. For some reason we don't
// understand, exiting from the thread may try to unload the DLL. Since the
// QDBusConnectionManager thread runs until the DLL is unloaded, we've got
// a deadlock: the main thread is waiting for the manager thread to exit,
// but the manager thread is attempting to acquire a lock to unload the DLL.
//
// We work around the issue by preventing the unload from happening in the
// first place.
//
// For this trick, see
// https://blogs.msdn.microsoft.com/oldnewthing/20131105-00/?p=2733
static HMODULE self;
GetModuleHandleEx(GET_MODULE_HANDLE_EX_FLAG_FROM_ADDRESS |
GET_MODULE_HANDLE_EX_FLAG_PIN,
reinterpret_cast<const wchar_t *>(&self), // any address in this DLL
&self);
}
QT_END_NAMESPACE
#endif
#endif // QT_NO_DBUS