From 8e7c52b9b997f021566ced5ef4f76e342cb37ff0 Mon Sep 17 00:00:00 2001
From: Bart Louwers <bart@emeel.net>
Date: Mon, 28 Jul 2025 23:24:21 +0200
Subject: [PATCH] Add MLN_CREATE_AUTORELEASEPOOL flag to create autoreleasepool
 in render loop (#3655)

---
 CMakeLists.txt                      | 20 +++++++++++++++++++-
 src/mbgl/renderer/renderer_impl.cpp |  4 ++++
 2 files changed, 23 insertions(+), 1 deletion(-)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 6f24a62dc..5e042ba95 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -17,6 +17,7 @@ option(MLN_USE_UNORDERED_DENSE "Use ankerl dense containers for performance" ON)
 option(MLN_USE_TRACY "Enable Tracy instrumentation" OFF)
 option(MLN_USE_RUST "Use components in Rust" OFF)
 option(MLN_CORE_INCLUDE_DEPS "Include depdendencies in static build of core" OFF)
+option(MLN_CREATE_AUTORELEASEPOOL "Create autoreleasepool in render loop" OFF)
 
 if (MLN_LEGACY_RENDERER)
     message(FATAL "The legacy renderer is no longer supported")
@@ -26,7 +27,6 @@ if (MLN_DRAWABLE_RENDERER)
     message(FATAL "Do not pass MLN_DRAWABLE_RENDERER, the drawable renderer is now the default")
 endif()
 
-
 if (MLN_WITH_CLANG_TIDY)
     find_program(CLANG_TIDY_COMMAND NAMES clang-tidy)
     if(NOT CLANG_TIDY_COMMAND)
@@ -1505,6 +1505,24 @@ set_target_properties(
         INTERFACE_MAPLIBRE_LICENSE ${PROJECT_SOURCE_DIR}/LICENSE.md
 )
 
+if(MLN_WITH_METAL AND MLN_CREATE_AUTORELEASEPOOL)
+    # When using the Metal backend, if there is is no AutoreleasePool, it will result
+    # in memory leaks when autoreleased objects are created.
+
+    # Platforms such as iOS and GLFW use ARC with @autoreleasepool blocks, for these platforms
+    # creating an AutoreleasePool is not neccesary (and in fact will not work).
+    # When using MapLibre Native with Metal on other platforms such as Node.js, you can pass
+    # this variable to ensure an AutoReleasePool is created in the render loop.
+    # See also:
+    # https://developer.apple.com/documentation/foundation/nsautoreleasepool
+    # https://github.com/maplibre/maplibre-native/issues/2928
+    # vendor/metal-cpp/README.md 'AutoreleasePools and Objects'
+    target_compile_definitions(
+        mbgl-core
+            PRIVATE MLN_CREATE_AUTORELEASEPOOL=1
+    )
+endif()
+
 set_property(TARGET mbgl-core PROPERTY FOLDER MapLibre)
 
 add_library(
diff --git a/src/mbgl/renderer/renderer_impl.cpp b/src/mbgl/renderer/renderer_impl.cpp
index 50dc45910..e20789009 100644
--- a/src/mbgl/renderer/renderer_impl.cpp
+++ b/src/mbgl/renderer/renderer_impl.cpp
@@ -93,6 +93,10 @@ void Renderer::Impl::render(const RenderTree& renderTree, const std::shared_ptr<
     assert(updateParameters);
 
 #if MLN_RENDER_BACKEND_METAL
+#if MLN_CREATE_AUTORELEASEPOOL
+    NS::SharedPtr pool = NS::TransferPtr(NS::AutoreleasePool::alloc()->init());
+#endif
+
     if constexpr (EnableMetalCapture) {
         const auto& mtlBackend = static_cast<mtl::RendererBackend&>(backend);