Fix thread-safety when calling request_resize()

src/detail/vst3/plugview.cpp

@@ -1,6 +1,7 @@
 #include "plugview.h"
 #include <clap/clap.h>
 #include <cassert>
+#include <thread>
 #include <iostream>
 
 WrappedView::WrappedView(const clap_plugin_t* plugin, const clap_plugin_gui_t* gui,
@@ -103,6 +104,8 @@ tresult PLUGIN_API WrappedView::isPlatformTypeSupported(FIDString type)
 
 tresult PLUGIN_API WrappedView::attached(void* parent, FIDString /*type*/)
 {
+  _main_thread_id = std::this_thread::get_id();
+
 #if WIN
   _window = {CLAP_WINDOW_API_WIN32, {parent}};
 #endif
@@ -259,6 +262,12 @@ tresult PLUGIN_API WrappedView::checkSizeConstraint(ViewRect* rect)
 
 bool WrappedView::request_resize(uint32_t width, uint32_t height)
 {
+  if (_main_thread_id != std::this_thread::get_id())
+  {
+    resize_request = {width, height};
+    return true;
+  }
+
   auto oldrect = _rect;
   _rect.right = _rect.left + (int32)width;
   _rect.bottom = _rect.top + (int32)height;
@@ -268,6 +277,7 @@ bool WrappedView::request_resize(uint32_t width, uint32_t height)
     _rect = oldrect;
     return false;
   }
+
   return true;
 }
 tresult WrappedView::setContentScaleFactor(IPlugViewContentScaleSupport::ScaleFactor factor)

src/detail/vst3/plugview.h

@@ -13,6 +13,8 @@
 #include <pluginterfaces/gui/iplugviewcontentscalesupport.h>
 #include <clap/clap.h>
 #include <functional>
+#include <thread>
+#include <atomic>
 
 using namespace Steinberg;
 
@@ -94,6 +96,22 @@ class WrappedView : public Steinberg::IPlugView,
   // wrapper needed interfaces
   bool request_resize(uint32_t width, uint32_t height);
 
+  // processed in ClapAsVst3::onIdle()
+  struct GuiResizeRequest
+  {
+    bool operator==(GuiResizeRequest const& other) const
+    {
+      return w == other.w && h == other.h;
+    }
+    bool operator!=(GuiResizeRequest const& other) const
+    {
+      return w != other.w || h != other.h;
+    }
+    uint32_t w, h;
+  };
+  constexpr static GuiResizeRequest invalid_size = {(uint32_t)-1, (uint32_t)-1};
+  std::atomic<GuiResizeRequest> resize_request{invalid_size};
+
  private:
   void ensure_ui();
   void drop_ui();
@@ -107,6 +125,7 @@ class WrappedView : public Steinberg::IPlugView,
   ViewRect _rect = {0, 0, 0, 0};
   bool _created = false;
   bool _attached = false;
+  std::thread::id _main_thread_id{};
 
 #if LIN
  public:

src/wrapasvst3.cpp

@@ -9,6 +9,7 @@
 #include "detail/vst3/process.h"
 #include "detail/vst3/parameter.h"
 #include "detail/clap/fsutil.h"
+#include <atomic>
 #include <locale>
 #include <sstream>
 
@@ -1292,6 +1293,15 @@ void ClapAsVst3::onIdle()
     _plugin->_plugin->on_main_thread(_plugin->_plugin);
   }
 
+  if (_wrappedview)
+  {
+    if (auto const size = _wrappedview->resize_request.exchange(WrappedView::invalid_size);
+        size != WrappedView::invalid_size)
+    {
+      _wrappedview->request_resize(size.w, size.h);
+    }
+  }
+
 #if LIN
   if (!_iRunLoop)  // don't process timers if we have a runloop.
                    // (but if we don't have a runloop on linux onIdle isn't called