From 044323e73a62d3b10188e0a591651cf6470b7721 Mon Sep 17 00:00:00 2001
From: Zach Lewis <zachcanbereached@gmail.com>
Date: Mon, 28 Sep 2026 16:41:10 -0400
Subject: [PATCH] Fix MSVC mutex initialization with older host runtimes

Disable constexpr mutex construction for MSVC builds, following OIIO's workaround for crashes with older runtimes bundled by host applications.

Signed-off-by: Zach Lewis <zachcanbereached@gmail.com>
---
 share/cmake/utils/CompilerFlags.cmake | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/share/cmake/utils/CompilerFlags.cmake b/share/cmake/utils/CompilerFlags.cmake
index 92f64fc0d1..167679d912 100644
--- a/share/cmake/utils/CompilerFlags.cmake
+++ b/share/cmake/utils/CompilerFlags.cmake
@@ -55,6 +55,10 @@ endif()
 
 if(USE_MSVC)
 
+    # Keep mutex initialization compatible with older MSVC runtimes in host applications.
+    # See https://github.com/AcademySoftwareFoundation/OpenImageIO/issues/4641
+    add_compile_definitions(_DISABLE_CONSTEXPR_MUTEX_CONSTRUCTOR)
+
     set(PLATFORM_COMPILE_OPTIONS "${PLATFORM_COMPILE_OPTIONS};/DUSE_MSVC")
 
     # /we4062 Enables warning in switch when an enumeration value is not explicitly handled.