Author: Danny Milosavljevic <dannym@friendly-machines.com>
Date: 2025-10-19
Subject: Work around silly (unused) atomic problem

Exclude static inline functions with atomics from C++ compilation.

block.cpp is the only C++ file in libdispatch and doesn't call the static
inline functions from lock.h.  These functions fail to compile in C++ mode
because stdatomic.h was only standardized for C++ in C++23.  Before C++23,
stdatomic.h doesn't provide memory_order_* constants.  We use GCC's libstdc++
which only provides C11 atomics in C++23 mode, not in C++11 mode.

Wrap all static inline functions in #ifndef __cplusplus so they are not
compiled when lock.h is included from C++ files, while keeping the type
definitions available.

--- a/src/shims/lock.h
+++ b/src/shims/lock.h
@@ -296,6 +296,7 @@
 #endif
 }
 
+#ifndef __cplusplus
 DISPATCH_ALWAYS_INLINE
 static inline void
 _dispatch_thread_event_signal(dispatch_thread_event_t dte)
@@ -341,6 +342,7 @@
 	_dispatch_sema4_dispose(&dte->dte_sema, _DSEMA4_POLICY_FIFO);
 #endif
 }
+#endif // __cplusplus
 
 #pragma mark - unfair lock
 
@@ -348,6 +350,7 @@
 	dispatch_lock dul_lock;
 } dispatch_unfair_lock_s, *dispatch_unfair_lock_t;
 
+#ifndef __cplusplus
 DISPATCH_NOT_TAIL_CALLED
 void _dispatch_unfair_lock_lock_slow(dispatch_unfair_lock_t l,
 		dispatch_lock_options_t options);
@@ -701,5 +704,6 @@
 		uint32_t flags);
 
 #endif // TARGET_OS_MAC
+#endif // __cplusplus
 
 #endif // __DISPATCH_SHIMS_LOCK__