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hack around Xlib deadlock #1923

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merged 6 commits into from
Dec 5, 2018
Merged

hack around Xlib deadlock #1923

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8c7b955
hack around Xlib deadlock
Be-ing Nov 28, 2018
c82b315
only hack around Xlib bug when running as an X client
Be-ing Nov 28, 2018
8fa52d4
use #if defined rather than #ifdef
Be-ing Nov 29, 2018
d60b287
fix #include
Be-ing Dec 3, 2018
bec5203
remove call to qt_x11_wait_for_window_manager
Be-ing Dec 3, 2018
7e5557a
add libqt5x11extras5-dev to Travis dependencies
Be-ing Dec 3, 2018
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3 changes: 3 additions & 0 deletions build/depends.py
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Original file line number Diff line number Diff line change
Expand Up @@ -245,7 +245,10 @@ def enabled_modules(build):
'QtTest',
'QtXml',
]

if qt5:
if build.platform_is_linux:
build.env.Append(LIBS = 'Qt5X11Extras')
qt_modules.extend([
# Keep alphabetized.
'QtConcurrent',
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42 changes: 41 additions & 1 deletion src/mixxx.cpp
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Expand Up @@ -81,10 +81,41 @@
#include "preferences/dialog/dlgprefmodplug.h"
#endif

#if defined(Q_OS_LINUX)
#include <QtGui/QX11Info>
#include <X11/Xlib.h>
#include <X11/Xlibint.h>
// Xlibint.h predates C++ and defines macros which conflict
// with references to std::max and std::min
#undef max
#undef min
#endif

namespace {

const mixxx::Logger kLogger("MixxxMainWindow");

// hack around https://gitlab.freedesktop.org/xorg/lib/libx11/issues/25
// https://bugs.launchpad.net/mixxx/+bug/1805559
#if defined(Q_OS_LINUX)
typedef Bool (*WireToErrorType)(Display*, XErrorEvent*, xError*);

const int NUM_HANDLERS = 256;
WireToErrorType __oldHandlers[NUM_HANDLERS] = {0};
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I still don't get the magic behind this array. Which unknown side effect sets the elements to a value other than 0? Currently the error interceptor does nothing except ignoring and dropping all incoming extension errors. This can be implemented in a much simpler way.

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Honestly, neither do I, nor do I understand the magic number 256. I've never worked with X11 code before, much less understand X's internals. I just copied and pasted from https://bugs.freedesktop.org/show_bug.cgi?id=59361#c4 and got it to build.

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256 because the error code is an unsigned char with values ranging from 0 to 255. But all slots are initialized with 0 (= nullptr) and are never updated.


Bool __xErrorHandler(Display* display, XErrorEvent* event, xError* error) {
// Call any previous handler first in case it needs to do real work.
auto code = static_cast<int>(event->error_code);
if (__oldHandlers[code] != NULL) {
__oldHandlers[code](display, event, error);
}

// Always return false so the error does not get passed to the normal
// application defined handler.
return False;
}
#endif

} // anonymous namespace

// static
Expand Down Expand Up @@ -150,7 +181,7 @@ MixxxMainWindow::MixxxMainWindow(QApplication* pApp, const CmdlineArgs& args)
setCentralWidget(m_pWidgetParent);

show();
#if defined(Q_WS_X11)
#if defined(Q_OS_LINUX)
// In asynchronous X11, the window will be mapped to screen
// some time after being asked to show itself on the screen.
extern void qt_x11_wait_for_window_manager(QWidget *mainWin);
Expand All @@ -169,6 +200,15 @@ MixxxMainWindow::~MixxxMainWindow() {
void MixxxMainWindow::initialize(QApplication* pApp, const CmdlineArgs& args) {
ScopedTimer t("MixxxMainWindow::initialize");

#if defined(Q_OS_LINUX)
// XESetWireToError will segfault if running as a Wayland client
if (pApp->platformName() == QStringLiteral("xcb")) {
for (auto i = 0; i < NUM_HANDLERS; ++i) {
XESetWireToError(QX11Info::display(), i, &__xErrorHandler);
}
}
#endif

UserSettingsPointer pConfig = m_pSettingsManager->settings();

Sandbox::initialize(QDir(pConfig->getSettingsPath()).filePath("sandbox.cfg"));
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