From b09e06a92041b1031eff69e6807507261244e568 Mon Sep 17 00:00:00 2001
From: NRK <nrk@disroot.org>
Date: Sat, 5 Apr 2025 16:33:47 +0000
Subject: [PATCH] osdep/threads: prefer using thread_local

C11 uses _Thread_local as the keyword, which thread_local macro
is defined to (inside of <threads.h>, which mpv doesn't use):
https://port70.net/~nsz/c/c11/n1570.html#7.26.1p3

C23 promotes thread_local to a keyword and marks _Thread_local
as obsolete and to be avoided in new code:
https://www.iso-9899.info/n3220.html#6.4.1p3

so just use thread_local directly, which is future-proof while
having a fallback define in osdep/threads.h for pre-C23 cases.
---
 osdep/compiler.h | 4 ++++
 osdep/io.c       | 2 +-
 osdep/threads.h  | 2 ++
 3 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/osdep/compiler.h b/osdep/compiler.h
index cb04fed81f..48693154ce 100644
--- a/osdep/compiler.h
+++ b/osdep/compiler.h
@@ -22,6 +22,10 @@
 #define MP_UNUSED
 #endif
 
+#if defined(__STDC_VERSION__) && (__STDC_VERSION__ < 202311L) && !defined(thread_local)
+#define thread_local _Thread_local
+#endif
+
 #if defined(__GNUC__) || defined(__clang__)
 #define PRINTF_ATTRIBUTE(a1, a2) __attribute__((format(printf, a1, a2)))
 #define SCANF_ATTRIBUTE(a1, a2) __attribute__((format(scanf, a1, a2)))
diff --git a/osdep/io.c b/osdep/io.c
index f7e24ba29a..5167b104a9 100644
--- a/osdep/io.c
+++ b/osdep/io.c
@@ -721,7 +721,7 @@ int mp_ftruncate64(int fd, off_t length)
     return -1;
 }
 
-_Thread_local
+thread_local
 static struct {
     DWORD errcode;
     char *errstring;
diff --git a/osdep/threads.h b/osdep/threads.h
index 4e9cf97baf..0e607598ff 100644
--- a/osdep/threads.h
+++ b/osdep/threads.h
@@ -9,4 +9,6 @@
 #include "threads-posix.h"
 #endif
 
+#include "osdep/compiler.h"  // for thread_local
+
 #endif