Move the wayland socket polling to a separate event thread

New event threads is introduced which calls poll() on the wayland fd,
instead of relying on the event dispatcher by using the QSocketNotifier.
This allows to call in the proper order the wl_display_prepare_read(),
poll() and wl_display_read_events() functions.

One thread is responsible for the default queue; when needed, it emit
a signal so that the main thread can dispatch the queue. Another thread
is responsible for the dedicated queue for frame callbacks; this thread
will dispatch events on the thread itself.

QWaylandWindow is updated to, instead of each window's dedicated event
queue, use this queue for frame callbacks.

Co-authored-by: Ratchanan Srirattanamet <ratchanan@ubports.com>
Task-number: QTBUG-66075
Change-Id: Ibb33ad7f4193b866d1b8d7a0405a94d59dcad5eb
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Eskil Abrahamsen Blomfeldt <eskil.abrahamsen-blomfeldt@qt.io>

3 files changed, 178 insertions, 0 deletions

diff --git a/tests/auto/client/CMakeLists.txt b/tests/auto/client/CMakeLists.txt
index ea6c4c1b..167cc607 100644
--- a/tests/auto/client/CMakeLists.txt
+++ b/tests/auto/client/CMakeLists.txt
@@ -6,6 +6,7 @@ add_subdirectory(client)
 add_subdirectory(datadevicev1)
 add_subdirectory(fullscreenshellv1)
 add_subdirectory(iviapplication)
+add_subdirectory(multithreaded)
 add_subdirectory(nooutput)
 add_subdirectory(output)
 add_subdirectory(primaryselectionv1)
diff --git a/tests/auto/client/multithreaded/CMakeLists.txt b/tests/auto/client/multithreaded/CMakeLists.txt
new file mode 100644
index 00000000..49d93297
--- /dev/null
+++ b/tests/auto/client/multithreaded/CMakeLists.txt
@@ -0,0 +1,12 @@
+# Generated from multithreaded.pro.
+
+#####################################################################
+## tst_multithreaded Test:
+#####################################################################
+
+qt_internal_add_test(tst_multithreaded
+    SOURCES
+        tst_multithreaded.cpp
+    PUBLIC_LIBRARIES
+        SharedClientTest
+)
diff --git a/tests/auto/client/multithreaded/tst_multithreaded.cpp b/tests/auto/client/multithreaded/tst_multithreaded.cpp
new file mode 100644
index 00000000..ce88a72f
--- /dev/null
+++ b/tests/auto/client/multithreaded/tst_multithreaded.cpp
@@ -0,0 +1,165 @@
+/****************************************************************************
+**
+** Copyright (C) 2018 The Qt Company Ltd.
+** Copyright (C) 2020 UBports Foundataion.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of the test suite of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:GPL-EXCEPT$
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and The Qt Company. For licensing terms
+** and conditions see https://www.qt.io/terms-conditions. For further
+** information use the contact form at https://www.qt.io/contact-us.
+**
+** GNU General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU
+** General Public License version 3 as published by the Free Software
+** Foundation with exceptions as appearing in the file LICENSE.GPL3-EXCEPT
+** included in the packaging of this file. Please review the following
+** information to ensure the GNU General Public License requirements will
+** be met: https://www.gnu.org/licenses/gpl-3.0.html.
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#include <unistd.h>
+#include <poll.h>
+
+#include <wayland-client-core.h>
+
+#include <QtGui/QScreen>
+#include <QAbstractEventDispatcher>
+#include <qpa/qplatformnativeinterface.h>
+
+#include "mockcompositor.h"
+
+using namespace MockCompositor;
+
+/*
+ * This class simulate a thread from another library which use poll() to wait
+ * for data from Wayland compositor.
+ */
+
+class ExternalWaylandReaderThread : public QThread
+{
+public:
+    ExternalWaylandReaderThread(struct wl_display *disp)
+        : QThread()
+        , m_disp(disp)
+    {
+        setObjectName(QStringLiteral("ExternalWaylandReader"));
+    }
+
+    ~ExternalWaylandReaderThread()
+    {
+        if (m_pipefd[1] != -1 && write(m_pipefd[1], "q", 1) == -1)
+            qWarning("Failed to write to the pipe: %s.", strerror(errno));
+
+        wait();
+    }
+
+protected:
+    void run() override
+    {
+        // we use this pipe to make the loop exit otherwise if we simply used a flag on the loop condition, if stop() gets
+        // called while poll() is blocking the thread will never quit since there are no wayland messages coming anymore.
+        struct Pipe
+        {
+            Pipe(int *fds)
+                : fds(fds)
+            {
+                if (::pipe(fds) != 0)
+                    qWarning("Pipe creation failed. Quitting may hang.");
+            }
+            ~Pipe()
+            {
+                if (fds[0] != -1) {
+                    close(fds[0]);
+                    close(fds[1]);
+                }
+            }
+
+            int *fds;
+        } pipe(m_pipefd);
+
+        struct wl_event_queue *a_queue = wl_display_create_queue(m_disp);
+        struct pollfd fds[2] = { { wl_display_get_fd(m_disp), POLLIN, 0 },
+                                 { m_pipefd[0], POLLIN, 0 } };
+
+        while (true) {
+            // No wl_proxy is assigned to this queue, thus guaranteed to be always empty.
+            Q_ASSERT(wl_display_prepare_read_queue(m_disp, a_queue) == 0);
+            wl_display_flush(m_disp);
+
+            // Wakeup every 10 seconds so that if Qt blocks in _read_events(),
+            // it won't last forever.
+            poll(fds, /* nfds */ 2, 10000);
+
+            if (fds[0].revents & POLLIN) {
+                wl_display_read_events(m_disp);
+            } else {
+                wl_display_cancel_read(m_disp);
+            }
+
+            if (fds[1].revents & POLLIN) {
+                char pipeIn;
+                read(m_pipefd[0], &pipeIn, 1);
+                if (pipeIn == 'q')
+                    break;
+            }
+        }
+
+        wl_event_queue_destroy(a_queue);
+    }
+
+private:
+    struct wl_display *m_disp;
+    int m_pipefd[2] = { -1, -1 };
+};
+
+class tst_multithreaded : public QObject, private DefaultCompositor
+{
+    Q_OBJECT
+private slots:
+    void initTestCase()
+    {
+        m_config.autoConfigure = true;
+        m_config.autoEnter = false;
+    }
+    void init()
+    {
+        // a test case is given new simulated thread.
+        QPlatformNativeInterface *native = QGuiApplication::platformNativeInterface();
+        struct wl_display *wl_dpy =
+                (struct wl_display *)native->nativeResourceForWindow("display", NULL);
+
+        m_extThread.reset(new ExternalWaylandReaderThread(wl_dpy));
+        m_extThread->start();
+    }
+    void cleanup()
+    {
+        QTRY_VERIFY2(isClean(), qPrintable(dirtyMessage()));
+    }
+
+    void mainThreadIsNotBlocked();
+
+public:
+    QScopedPointer<ExternalWaylandReaderThread> m_extThread;
+};
+
+void tst_multithreaded::mainThreadIsNotBlocked()
+{
+    QElapsedTimer timer;
+    timer.start();
+
+    QTest::qWait(100);
+    QVERIFY(timer.elapsed() < 200);
+}
+
+QCOMPOSITOR_TEST_MAIN(tst_multithreaded)
+#include "tst_multithreaded.moc"