Abandon C++ std::atomic

It doesn't work in an extern "C" section.

Author: morrisonlevi

Zend/zend_globals.h

@@ -37,18 +37,19 @@
 #include "zend_arena.h"
 
 /* Unlike stdbool.h, not all supported compilers support stdatomic.h in C++
- * mode. So, conditionally include <atomic> or <stdatomic.h> depending on
- * whether the compiler is in C++ mode or not. This restricts us to functions,
- * types, and macros which are present in both, which is a drag.
+ * mode. There have beeen discussions to fix this for C++23/C23, but for
+ * existing compilers there isn't much to do. Using C++'s std::atomic_bool
+ * doesn't work because templates aren't available in extern C code. In this
+ * case, fall back to no atomics.
+ * TODO: move this stuff to a configure script because for this to be ABI safe,
+ *       a check that sizeof(atomic_bool) == sizeof(bool) needs to done.
  */
-#ifdef __cplusplus
-#include <atomic>
-using std::atomic_bool;
-#elif !defined(__STDC_NO_ATOMICS__)
-#include <stdatomic.h>
-#else
+#if defined(__cplusplus) || __STDC_VERSION__ < 201112L || defined(__STDC_NO_ATOMICS__)
 // fall back to non-atomics
-typedef bool atomic_bool
+typedef bool maybe_atomic_bool;
+#else
+#include <stdatomic.h>
+typedef atomic_bool maybe_atomic_bool;
 #endif
 
 /* Define ZTS if you want a thread-safe Zend */
@@ -199,12 +200,8 @@ struct _zend_executor_globals {
 
 	HashTable *in_autoload;
 
-	/* sizeof atomic_bool is not guaranteed to be the same as sizeof bool,
-	 * but it's somewhat common. The atomic_bools are left by the other
-	 * bools so that the struct packs nicely for such platforms.
-	 */
-	atomic_bool vm_interrupt;
-	atomic_bool timed_out;
+	maybe_atomic_bool vm_interrupt;
+	maybe_atomic_bool timed_out;
 	bool full_tables_cleanup;
 
 	/* for extended information support */