https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86846
--- Comment #5 from Jonathan Wakely <redi at gcc dot gnu.org> ---
This should do it:
--- a/libstdc++-v3/src/c++17/memory_resource.cc
+++ b/libstdc++-v3/src/c++17/memory_resource.cc
@@ -25,6 +25,7 @@
#include <memory_resource>
#include <atomic>
#include <new>
+#include <bits/std_mutex.h>
namespace std _GLIBCXX_VISIBILITY(default)
{
@@ -81,7 +82,31 @@ namespace pmr
constant_init<newdel_res_t> newdel_res{};
constant_init<null_res_t> null_res{};
+#if ATOMIC_POINTER_LOCK_FREE == 2
constant_init<atomic<memory_resource*>> default_res{&newdel_res.obj};
+#else
+ struct locking_atomic
+ {
+ constexpr locking_atomic(memory_resource* r) : val(r) { }
+ mutex mx;
+ memory_resource* val;
+
+ memory_resource* load()
+ {
+ lock_guard<mutex> lock(mx);
+ return val;
+ }
+
+ memory_resource* exchange(memory_resource* r)
+ {
+ lock_guard<mutex> lock(mx);
+ auto prev = val;
+ val = r;
+ return prev;
+ }
+ };
+ constant_init<locking_atomic> default_res{&newdel_res.obj};
+#endif
} // namespace
memory_resource*
