disable shared mutex on some platforms

Author: iskakaushik

flutter_vma/BUILD.gn

@@ -2,12 +2,18 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
+import("//flutter/flutter_vma/config.gni")
+
 source_set("flutter_vma") {
   sources = [
     "flutter_vma.cc",
     "flutter_vma.h",
   ]
 
+  if (disable_vma_stl_shared_mutex) {
+    defines = [ "VMA_USE_STL_SHARED_MUTEX=0" ]
+  }
+
   deps = [
     "//third_party/vulkan-deps/vulkan-headers/src:vulkan_headers",
     "//third_party/vulkan_memory_allocator",

flutter_vma/config.gni

@@ -0,0 +1,7 @@
+# Copyright 2013 The Flutter Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+declare_args() {
+  disable_vma_stl_shared_mutex = false
+}

tools/gn

@@ -438,6 +438,10 @@ def to_gn_args(args):
     gn_args['skia_use_vulkan'] = True
     gn_args['skia_use_vma'] = False
     gn_args['shell_enable_vulkan'] = True
+    # Disable VMA's use of std::shared_mutex in environments where the
+    # standard library doesn't support it.
+    if args.target_os == 'ios' or sys.platform.startswith(('cygwin', 'win')):
+      gn_args['disable_vma_stl_shared_mutex'] = True
 
   # We should not need a special case for x86, but this seems to introduce text relocations
   # even with -fPIC everywhere.