renderer: implemented function to wait for workers in the main thread

The workers run in separate threads meaning if any significant change is made
(e.g. parameters changing, or even closing the program), these workers may still
be mid-render. This is particularly problematic when closing since the nodes a
worker is rendering may be deleted mid-render. Render backends now have a
function that pauses the main thread (but starts a second event loop so the UI
isn't frozen) until the worker threads are all finished. This way, massive
changes can be made safely without race conditions.

app/render/backend/renderbackend.cpp

@@ -3,6 +3,9 @@
 #include <QDateTime>
 #include <QThread>
 
+#include "core.h"
+#include "window/mainwindow/mainwindow.h"
+
 RenderBackend::RenderBackend(QObject *parent) :
   QObject(parent),
   compiled_(false),
@@ -12,6 +15,8 @@ RenderBackend::RenderBackend(QObject *parent) :
   recompile_queued_(false),
   input_update_queued_(false)
 {
+  // FIXME: Don't create in CLI mode
+  cancel_dialog_ = new RenderCancelDialog(Core::instance()->main_window());
 }
 
 bool RenderBackend::Init()
@@ -30,6 +35,8 @@ bool RenderBackend::Init()
     thread->start(QThread::LowPriority);
   }
 
+  cancel_dialog_->SetWorkerCount(threads_.size());
+
   started_ = InitInternal();
 
   // Connects workers and moves them to their respective threads
@@ -50,6 +57,8 @@ void RenderBackend::Close()
 
   started_ = false;
 
+  CancelQueue();
+
   Decompile();
 
   CloseInternal();
@@ -81,6 +90,8 @@ const QString &RenderBackend::GetError() const
 void RenderBackend::SetViewerNode(ViewerOutput *viewer_node)
 {
   if (viewer_node_ != nullptr) {
+    CancelQueue();
+
     DisconnectViewer(viewer_node_);
 
     Decompile();
@@ -297,6 +308,7 @@ void RenderBackend::CacheNext()
       render_job_info_.insert(cache_frame, job_time);
 
       SetWorkerBusyState(worker, true);
+      cancel_dialog_->WorkerStarted();
 
       QMetaObject::invokeMethod(worker,
                                 "Render",
@@ -312,6 +324,20 @@ ViewerOutput *RenderBackend::viewer_node() const
   return copied_viewer_node_;
 }
 
+void RenderBackend::CancelQueue()
+{
+  cache_queue_.clear();
+
+  int busy = 0;
+  for (int i=0;i<processor_busy_state_.size();i++) {
+    if (processor_busy_state_.at(i))
+      busy++;
+  }
+  qDebug() << this << "has" << busy << "busy workers";
+
+  cancel_dialog_->RunIfWorkersAreBusy();
+}
+
 bool RenderBackend::ViewerIsConnected() const
 {
   return viewer_node_ != nullptr;
@@ -375,6 +401,9 @@ void RenderBackend::InitWorkers()
     // Connect to it
     ConnectWorkerToThis(processor);
 
+    // Connect cancel dialog to it
+    connect(processor, &RenderWorker::CompletedCache, cancel_dialog_, &RenderCancelDialog::WorkerDone, Qt::QueuedConnection);
+
     // Finally, we can move it to its own thread
     processor->moveToThread(thread);