Use _Thread_local for thread-local storage

init.c currently does not compile for Windows with newer versions of Clang
because it declares `__dispatch_tsd` with `__thread` but shims/tsd.h declares it
with `__declspec(thread)`. Use the standard `_Thread_local` instead.

Author: adierking

CMakeLists.txt

@@ -102,7 +102,7 @@ option(USE_GOLD_LINKER "use the gold linker" ${USE_GOLD_LINKER_DEFAULT})
 
 option(USE_LLD_LINKER "use the lld linker" OFF)
 
-option(ENABLE_THREAD_LOCAL_STORAGE "enable usage of thread local storage via __thread" ON)
+option(ENABLE_THREAD_LOCAL_STORAGE "enable usage of thread local storage via _Thread_local" ON)
 set(DISPATCH_USE_THREAD_LOCAL_STORAGE ${ENABLE_THREAD_LOCAL_STORAGE})
 
 if(CMAKE_SYSTEM_NAME STREQUAL Linux OR

cmake/config.h.in

@@ -2,7 +2,7 @@
 /* Define if building pthread work queues from source */
 #cmakedefine01 DISPATCH_USE_INTERNAL_WORKQUEUE
 
-/* Enable usage of thread local storage via __thread */
+/* Enable usage of thread local storage via _Thread_local */
 #cmakedefine01 DISPATCH_USE_THREAD_LOCAL_STORAGE
 
 /* Define to 1 if you have the declaration of `CLOCK_MONOTONIC', and to 0 if

src/init.c

@@ -112,7 +112,7 @@ void (*_dispatch_end_NSAutoReleasePool)(void *);
 #endif
 
 #if DISPATCH_USE_THREAD_LOCAL_STORAGE
-__thread struct dispatch_tsd __dispatch_tsd;
+_Thread_local struct dispatch_tsd __dispatch_tsd;
 #if defined(_WIN32)
 DWORD __dispatch_tsd_key;
 #else

src/shims/tsd.h

@@ -115,7 +115,6 @@ _dispatch_thread_key_create(DWORD *k, void (DISPATCH_TSD_DTOR_CC *d)(void *))
 	dispatch_assert_zero((*k = FlsAlloc(d)));
 }
 
-extern __declspec(thread) struct dispatch_tsd __dispatch_tsd;
 extern DWORD __dispatch_tsd_key;
 
 #else
@@ -127,7 +126,6 @@ _dispatch_thread_key_create(pthread_key_t *k, void (DISPATCH_TSD_DTOR_CC *d)(voi
 	dispatch_assert_zero(pthread_key_create(k, d));
 }
 
-extern __thread struct dispatch_tsd __dispatch_tsd;
 extern pthread_key_t __dispatch_tsd_key;
 
 #endif
@@ -156,6 +154,8 @@ struct dispatch_tsd {
 	void *dispatch_deferred_items_key;
 };
 
+extern _Thread_local struct dispatch_tsd __dispatch_tsd;
+
 extern void libdispatch_tsd_init(void);
 extern void _libdispatch_tsd_cleanup(void *ctx);