source/blender/gpu/metal/mtl_command_buffer.mm

@@ -20,7 +20,7 @@ using namespace blender::gpu;
 namespace blender::gpu {
 
 /* Counter for active command buffers. */
-int MTLCommandBufferManager::num_active_cmd_bufs = 0;
+volatile std::atomic<int> MTLCommandBufferManager::num_active_cmd_bufs_in_system = 0;
 
 /* -------------------------------------------------------------------- */
 /** \name MTLCommandBuffer initialization and render coordination.
@@ -50,7 +50,7 @@ id<MTLCommandBuffer> MTLCommandBufferManager::ensure_begin()
      *
      * NOTE: We currently stall until completion of GPU work upon ::submit if we have reached the
      * in-flight command buffer limit. */
-    BLI_assert(MTLCommandBufferManager::num_active_cmd_bufs <
+    BLI_assert(MTLCommandBufferManager::num_active_cmd_bufs_in_system <
                GHOST_ContextCGL::max_command_buffer_count);
 
     if (G.debug & G_DEBUG_GPU) {
@@ -68,7 +68,7 @@ id<MTLCommandBuffer> MTLCommandBufferManager::ensure_begin()
     }
 
     [active_command_buffer_ retain];
-    MTLCommandBufferManager::num_active_cmd_bufs++;
+    context_.main_command_buffer.inc_active_command_buffer_count();
 
     /* Ensure we begin new Scratch Buffer if we are on a new frame. */
     MTLScratchBufferManager &mem = context_.memory_manager;
@@ -90,6 +90,12 @@ bool MTLCommandBufferManager::submit(bool wait)
 {
   /* Skip submission if command buffer is empty. */
   if (empty_ || active_command_buffer_ == nil) {
+    if (wait) {
+      /* Wait for any previously submitted work on this context to complete. */
+      while (context_.main_command_buffer.get_active_command_buffer_count()) {
+        std::this_thread::sleep_for(std::chrono::milliseconds(1));
+      }
+    }
     return false;
   }
 
@@ -123,7 +129,7 @@ bool MTLCommandBufferManager::submit(bool wait)
     [cmd_buffer_ref release];
 
     /* Decrement count. */
-    MTLCommandBufferManager::num_active_cmd_bufs--;
+    context_.main_command_buffer.dec_active_command_buffer_count();
   }];
 
   /* Submit command buffer to GPU. */
@@ -131,7 +137,7 @@ bool MTLCommandBufferManager::submit(bool wait)
 
   /* If we have too many active command buffers in flight, wait until completed to avoid running
    * out. We can increase */
-  if (MTLCommandBufferManager::num_active_cmd_bufs >=
+  if (MTLCommandBufferManager::num_active_cmd_bufs_in_system >=
       (GHOST_ContextCGL::max_command_buffer_count - 1))
   {
     wait = true;

source/blender/gpu/metal/mtl_context.hh

@@ -548,8 +548,8 @@ class MTLCommandBufferManager {
   friend class MTLContext;
 
  public:
-  /* Counter for active command buffers. */
-  static int num_active_cmd_bufs;
+  /* Counter for all active command buffers. */
+  static volatile std::atomic<int> num_active_cmd_bufs_in_system;
 
  private:
   /* Associated Context and properties. */
@@ -559,6 +559,7 @@ class MTLCommandBufferManager {
   /* CommandBuffer tracking. */
   id<MTLCommandBuffer> active_command_buffer_ = nil;
   id<MTLCommandBuffer> last_submitted_command_buffer_ = nil;
+  volatile std::atomic<int> num_active_cmd_bufs = 0;
 
   /* Active MTLCommandEncoders. */
   enum {
@@ -653,6 +654,24 @@ class MTLCommandBufferManager {
   void push_debug_group(const char *name, int index);
   void pop_debug_group();
 
+  void inc_active_command_buffer_count()
+  {
+    num_active_cmd_bufs_in_system++;
+    num_active_cmd_bufs++;
+  }
+
+  void dec_active_command_buffer_count()
+  {
+    BLI_assert(num_active_cmd_bufs_in_system > 0 && num_active_cmd_bufs > 0);
+    num_active_cmd_bufs_in_system--;
+    num_active_cmd_bufs--;
+  }
+
+  int get_active_command_buffer_count()
+  {
+    return num_active_cmd_bufs;
+  }
+
  private:
   /* Begin new command buffer. */
   id<MTLCommandBuffer> ensure_begin();

source/blender/gpu/metal/mtl_context.mm

@@ -2706,7 +2706,7 @@ void present(MTLRenderPassDescriptor *blit_descriptor,
    * possible. This command buffer is separate as it does not utilize the global state
    * for rendering as the main context does. */
   id<MTLCommandBuffer> cmdbuf = [ctx->queue commandBuffer];
-  MTLCommandBufferManager::num_active_cmd_bufs++;
+  ctx->main_command_buffer.inc_active_command_buffer_count();
 
   /* Do Present Call and final Blit to MTLDrawable. */
   id<MTLRenderCommandEncoder> enc = [cmdbuf renderCommandEncoderWithDescriptor:blit_descriptor];
@@ -2739,8 +2739,10 @@ void present(MTLRenderPassDescriptor *blit_descriptor,
     [cmd_buffer_ref release];
 
     /* Decrement count */
-    MTLCommandBufferManager::num_active_cmd_bufs--;
-    MTL_LOG_INFO("Active command buffers: %d", MTLCommandBufferManager::num_active_cmd_bufs);
+    ctx->main_command_buffer.dec_active_command_buffer_count();
+
+    MTL_LOG_INFO("Active command buffers: %d",
+                 int(MTLCommandBufferManager::num_active_cmd_bufs_in_system));
 
     /* Drawable count and latency management. */
     MTLContext::max_drawables_in_flight--;