[libcalamares] Reimplement JobQueue::queueChanged

- switch to QStringList as parameter, since consumers (that is,
  the debug dialog, which is what this is for) are interested
  just in the **names** of the jobs.
- to allow mutex locking in const methods, mark them mutable.

src/calamares/DebugWindow.cpp

@@ -102,14 +102,8 @@ DebugWindow::DebugWindow()
 
     // JobQueue page
     m_ui->jobQueueText->setReadOnly( true );
-    connect( JobQueue::instance(), &JobQueue::queueChanged, this, [this]( const JobList& jobs ) {
-        QStringList text;
-        for ( const auto& job : jobs )
-        {
-            text.append( job->prettyName() );
-        }
-
-        m_ui->jobQueueText->setText( text.join( '\n' ) );
+    connect( JobQueue::instance(), &JobQueue::queueChanged, this, [this]( const QStringList& jobs ) {
+        m_ui->jobQueueText->setText( jobs.join( '\n' ) );
     } );
 
     // Modules page
@@ -193,7 +187,8 @@ DebugWindow::DebugWindow()
 #endif
     ] {
                  QString moduleName = m_ui->modulesListView->currentIndex().data().toString();
-                 Module* module = ModuleManager::instance()->moduleInstance( ModuleSystem::InstanceKey::fromString( moduleName ) );
+                 Module* module
+                     = ModuleManager::instance()->moduleInstance( ModuleSystem::InstanceKey::fromString( moduleName ) );
                  if ( module )
                  {
                      m_module = module->configurationMap();

src/libcalamares/JobQueue.cpp

@@ -151,6 +151,24 @@ public:
         QMetaObject::invokeMethod( m_queue, "finish", Qt::QueuedConnection );
     }
 
+    /** @brief The names of the queued (not running!) jobs.
+     */
+    QStringList queuedJobs() const
+    {
+        QMutexLocker qlock( &m_enqueMutex );
+        QStringList l;
+        l.reserve( m_queuedJobs->count() );
+        for ( const auto& j : *m_queuedJobs )
+        {
+            l << j.job->prettyName();
+        }
+        return l;
+    }
+
+private:
+    /* This is called **only** from run(), while m_runMutex is
+     * already locked, so we can use the m_runningJobs member safely.
+     */
     void emitProgress( qreal percentage ) const
     {
         percentage = qBound( 0.0, percentage, 1.0 );
@@ -172,10 +190,8 @@ public:
             m_queue, "progress", Qt::QueuedConnection, Q_ARG( qreal, progress ), Q_ARG( QString, message ) );
     }
 
-
-private:
-    QMutex m_runMutex;
-    QMutex m_enqueMutex;
+    mutable QMutex m_runMutex;
+    mutable QMutex m_enqueMutex;
 
     std::unique_ptr< WeightedJobList > m_runningJobs = std::make_unique< WeightedJobList >();
     std::unique_ptr< WeightedJobList > m_queuedJobs = std::make_unique< WeightedJobList >();
@@ -242,6 +258,7 @@ JobQueue::enqueue( int moduleWeight, const JobList& jobs )
 {
     Q_ASSERT( !m_thread->isRunning() );
     m_thread->enqueue( moduleWeight, jobs );
+    emit queueChanged( m_thread->queuedJobs() );
 }
 
 void
@@ -249,6 +266,7 @@ JobQueue::finish()
 {
     m_finished = true;
     emit finished();
+    emit queueChanged( m_thread->queuedJobs() );
 }
 
 GlobalStorage*

src/libcalamares/JobQueue.h

@@ -82,6 +82,14 @@ signals:
      */
     void failed( const QString& message, const QString& details );
 
+    /** @brief Reports the names of jobs in the queue.
+     *
+     * When jobs are added via enqueue(), or when the queue otherwise
+     * changes, the **names** of the jobs are reported. This is
+     * primarily for debugging purposes.
+     */
+    void queueChanged( const QStringList& jobNames );
+
 private:
     void finish();