Introduce KillPrompt class

This encapsulates running and querying for the killer helper
and allows to more easily re-use it for Wayland windows.

src/CMakeLists.txt

@@ -114,6 +114,7 @@ target_sources(kwin PRIVATE
     keyboard_layout.cpp
     keyboard_layout_switching.cpp
     keyboard_repeat.cpp
+    killprompt.cpp
     killwindow.cpp
     kscreenintegration.cpp
     layers.cpp

src/killprompt.cpp

@@ -0,0 +1,86 @@
+/*
+ * SPDX-FileCopyrightText: 2023 Kai Uwe Broulik <kde@broulik.de>
+ *
+ * SPDX-License-Identifier: GPL-2.0-or-later
+ */
+
+#include "killprompt.h"
+
+#include "client_machine.h"
+#include "x11window.h"
+
+#include <QDir>
+#include <QFileInfo>
+#include <QString>
+
+namespace KWin
+{
+
+KillPrompt::KillPrompt(Window *window)
+    : m_window(window)
+{
+    Q_ASSERT(qobject_cast<X11Window *>(window));
+
+    m_process.setProcessChannelMode(QProcess::ForwardedChannels);
+
+    const QFileInfo binaryInfo(KWIN_KILLER_BIN);
+    const QFileInfo buildDirBinary{QDir{QCoreApplication::applicationDirPath()}, binaryInfo.fileName()};
+
+    if (buildDirBinary.exists()) {
+        m_process.setProgram(buildDirBinary.absoluteFilePath());
+    } else {
+        m_process.setProgram(KWIN_KILLER_BIN);
+    }
+}
+
+bool KillPrompt::isRunning() const
+{
+    return m_process.state() == QProcess::Running;
+}
+
+void KillPrompt::start(quint32 timestamp)
+{
+    if (isRunning()) {
+        return;
+    }
+
+    QProcessEnvironment env = kwinApp()->processStartupEnvironment();
+
+    QString wid;
+    QString timestampString;
+    QString hostname = QStringLiteral("localhost");
+
+    if (auto *x11Window = qobject_cast<X11Window *>(m_window)) {
+        wid = QString::number(x11Window->window());
+        timestampString = QString::number(timestamp);
+        if (!x11Window->clientMachine()->isLocal()) {
+            hostname = x11Window->clientMachine()->hostName();
+        }
+    }
+
+    QStringList args{
+        QStringLiteral("--pid"),
+        QString::number(m_window->pid()),
+        QStringLiteral("--windowname"),
+        m_window->captionNormal(),
+        QStringLiteral("--applicationname"),
+        m_window->resourceClass(),
+        QStringLiteral("--wid"),
+        wid,
+        QStringLiteral("--hostname"),
+        hostname,
+        QStringLiteral("--timestamp"),
+        timestampString,
+    };
+
+    m_process.setArguments(args);
+    m_process.setProcessEnvironment(env);
+    m_process.start();
+}
+
+void KillPrompt::quit()
+{
+    m_process.terminate();
+}
+
+} // namespace KWin

src/killprompt.h

@@ -0,0 +1,45 @@
+/*
+ * SPDX-FileCopyrightText: 2023 Kai Uwe Broulik <kde@broulik.de>
+ *
+ * SPDX-License-Identifier: GPL-2.0-or-later
+ */
+
+#pragma once
+
+#include <QProcess>
+
+namespace KWin
+{
+
+class Window;
+
+class KillPrompt
+{
+public:
+    /**
+     * @brief Creates a kill helper process.
+     * @param window The window to kill, must be an X11Window
+     */
+    explicit KillPrompt(Window *window);
+
+    /**
+     * @brief Whether the kill helper process is currently running.
+     */
+    bool isRunning() const;
+
+    /**
+     * @brief Starts the kill helper process.
+     * @param timestamp The X activation timestamp.
+     */
+    void start(quint32 timestamp = 0);
+    /**
+     * @brief Terminate the kill helper process.
+     */
+    void quit();
+
+private:
+    Window *m_window = nullptr;
+    QProcess m_process;
+};
+
+} // namespace KWin

src/x11window.cpp

@@ -23,6 +23,7 @@
 #include "effect/effecthandler.h"
 #include "focuschain.h"
 #include "group.h"
+#include "killprompt.h"
 #include "netinfo.h"
 #include "placement.h"
 #include "scene/surfaceitem_x11.h"
@@ -290,7 +291,6 @@ X11Window::X11Window()
     , blocks_compositing(false)
     , in_group(nullptr)
     , ping_timer(nullptr)
-    , m_killHelperPID(0)
     , m_pingTimestamp(XCB_TIME_CURRENT_TIME)
     , m_userTime(XCB_TIME_CURRENT_TIME) // Not known yet
     , allowed_actions()
@@ -356,9 +356,8 @@ X11Window::~X11Window()
 {
     delete info;
 
-    if (m_killHelperPID && !::kill(m_killHelperPID, 0)) { // means the process is alive
-        ::kill(m_killHelperPID, SIGTERM);
-        m_killHelperPID = 0;
+    if (m_killPrompt) {
+        m_killPrompt->quit();
     }
 
     Q_ASSERT(!isInteractiveMoveResize());
@@ -2106,15 +2105,14 @@ void X11Window::gotPing(xcb_timestamp_t timestamp)
 
     setUnresponsive(false);
 
-    if (m_killHelperPID && !::kill(m_killHelperPID, 0)) { // means the process is alive
-        ::kill(m_killHelperPID, SIGTERM);
-        m_killHelperPID = 0;
+    if (m_killPrompt) {
+        m_killPrompt->quit();
     }
 }
 
 void X11Window::killProcess(bool ask, xcb_timestamp_t timestamp)
 {
-    if (m_killHelperPID && !::kill(m_killHelperPID, 0)) { // means the process is alive
+    if (m_killPrompt && m_killPrompt->isRunning()) {
         return;
     }
     Q_ASSERT(!ask || timestamp != XCB_TIME_CURRENT_TIME);
@@ -2132,16 +2130,10 @@ void X11Window::killProcess(bool ask, xcb_timestamp_t timestamp)
             ::kill(pid, SIGTERM);
         }
     } else {
-        QString hostname = clientMachine()->isLocal() ? QStringLiteral("localhost") : clientMachine()->hostName();
-        // execute helper from build dir or the system installed one
-        const QFileInfo buildDirBinary{QDir{QCoreApplication::applicationDirPath()}, QStringLiteral("kwin_killer_helper")};
-        QProcess::startDetached(buildDirBinary.exists() ? buildDirBinary.absoluteFilePath() : KWIN_KILLER_BIN,
-                                QStringList() << QStringLiteral("--pid") << QString::number(unsigned(pid)) << QStringLiteral("--hostname") << hostname
-                                              << QStringLiteral("--windowname") << captionNormal()
-                                              << QStringLiteral("--applicationname") << resourceClass()
-                                              << QStringLiteral("--wid") << QString::number(window())
-                                              << QStringLiteral("--timestamp") << QString::number(timestamp),
-                                QString(), &m_killHelperPID);
+        if (!m_killPrompt) {
+            m_killPrompt = std::make_unique<KillPrompt>(this);
+        }
+        m_killPrompt->start(timestamp);
     }
 }
 

src/x11window.h

@@ -32,6 +32,8 @@ class KStartupInfoId;
 namespace KWin
 {
 
+class KillPrompt;
+
 /**
  * @brief Defines Predicates on how to search for a Client.
  *
@@ -479,7 +481,7 @@ private:
     QString cap_normal, cap_iconic, cap_suffix;
     Group *in_group;
     QTimer *ping_timer;
-    qint64 m_killHelperPID;
+    std::unique_ptr<KillPrompt> m_killPrompt;
     xcb_timestamp_t m_pingTimestamp;
     xcb_timestamp_t m_userTime;
     NET::Actions allowed_actions;