Backends: Metal: Add dispatch synchronization. (#5447)

backends/imgui_impl_metal.mm

@@ -12,6 +12,8 @@
 
 // CHANGELOG
 // (minor and older changes stripped away, please see git history for details)
+//  2022-07-05: Metal: Add dispatch synchronization.
+//  2022-06-30: Metal: Use __bridge for ARC based systems.
 //  2022-06-01: Metal: Fixed null dereference on exit inside command buffer completion handler.
 //  2022-04-27: Misc: Store backend data in a per-context struct, allowing to use this backend with multiple contexts.
 //  2022-01-03: Metal: Ignore ImDrawCmd where ElemCount == 0 (very rare but can technically be manufactured by user code).
@@ -295,10 +297,13 @@ void ImGui_ImplMetal_RenderDrawData(ImDrawData* drawData, id<MTLCommandBuffer> c
         dispatch_async(dispatch_get_main_queue(), ^{
             ImGui_ImplMetal_Data* bd = ImGui_ImplMetal_GetBackendData();
             if (bd != NULL)
+            {
+                @synchronized(bd->SharedMetalContext.bufferCache)
                 {
                     [bd->SharedMetalContext.bufferCache addObject:vertexBuffer];
                     [bd->SharedMetalContext.bufferCache addObject:indexBuffer];
                 }
+            }
         });
     }];
 }
@@ -440,6 +445,8 @@ void ImGui_ImplMetal_DestroyDeviceObjects()
 {
     uint64_t now = GetMachAbsoluteTimeInSeconds();
 
+    @synchronized(self.bufferCache)
+    {
         // Purge old buffers that haven't been useful for a while
         if (now - self.lastBufferCachePurge > 1.0)
         {
@@ -463,6 +470,7 @@ void ImGui_ImplMetal_DestroyDeviceObjects()
             bestCandidate.lastReuseTime = now;
             return bestCandidate;
         }
+    }
 
     // No luck; make a new buffer
     id<MTLBuffer> backing = [device newBufferWithLength:length options:MTLResourceStorageModeShared];

docs/CHANGELOG.txt

@@ -43,6 +43,7 @@ Other Changes:
   Enter keep the input active and select all text.
 - Misc: io.Framerate moving average now converge in 60 frames instead of 120. (#5236, #4138)
 - Backends: Metal: Use __bridge for ARC based systems. (#5403) [@stack]
+- Backends: Metal: Add dispatch synchronization. (#5447) [@luigifcruz]
 - Backends: OSX: Fixes to support full app creation in C++. (#5403) [@stack]