win: lazy-load [GS]etThreadDescription symbols (#4679)

Said symbols are not by default available on Windows Server 2016 but
libuv can still use them when
api-ms-win-core-processthreads-l1-1-3.dll is present.

Fixes: https://github.com/libuv/libuv/issues/4677

docs/src/threading.rst

@@ -146,6 +146,8 @@ Threads
     a thread name can be: Linux, IBM i (16), macOS (64), Windows (32767), and NetBSD (32), etc. `uv_thread_setname()`
     will truncate it in case `name` is larger than the limit of the platform.
 
+    Not supported on Windows Server 2016, returns `UV_ENOSYS`.
+
     .. versionadded:: 1.50.0
 
 .. c:function:: int uv_thread_getname(uv_thread_t* tid, char* name, size_t* size)
@@ -155,6 +157,8 @@ Threads
     The buffer should be large enough to hold the name of the thread plus the trailing NUL, or it will be truncated to fit
     with the trailing NUL.
 
+    Not supported on Windows Server 2016, returns `UV_ENOSYS`.
+
     .. versionadded:: 1.50.0
 
 .. c:function:: int uv_thread_setpriority(uv_thread_t tid, int priority)

src/win/thread.c

@@ -57,6 +57,9 @@ STATIC_ASSERT(sizeof(uv_thread_t) <= sizeof(void*));
 
 static uv_key_t uv__current_thread_key;
 static uv_once_t uv__current_thread_init_guard = UV_ONCE_INIT;
+static uv_once_t uv__thread_name_once = UV_ONCE_INIT;
+HRESULT (WINAPI *pGetThreadDescription)(HANDLE, PWSTR*);
+HRESULT (WINAPI *pSetThreadDescription)(HANDLE, PCWSTR);
 
 
 static void uv__init_current_thread_key(void) {
@@ -278,12 +281,28 @@ int uv_thread_equal(const uv_thread_t* t1, const uv_thread_t* t2) {
 }
 
 
+static void uv__thread_name_init_once(void) {
+  HMODULE m;
+
+  m = GetModuleHandleA("api-ms-win-core-processthreads-l1-1-3.dll");
+  if (m != NULL) {
+    pGetThreadDescription = (void*) GetProcAddress(m, "GetThreadDescription");
+    pSetThreadDescription = (void*) GetProcAddress(m, "SetThreadDescription");
+  }
+}
+
+
 int uv_thread_setname(const char* name) {
   HRESULT hr;
   WCHAR* namew;
   int err;
   char namebuf[UV_PTHREAD_MAX_NAMELEN_NP];
 
+  uv_once(&uv__thread_name_once, uv__thread_name_init_once);
+
+  if (pSetThreadDescription == NULL)
+    return UV_ENOSYS;
+
   if (name == NULL)
     return UV_EINVAL;
 
@@ -295,7 +314,7 @@ int uv_thread_setname(const char* name) {
   if (err)
     return err;
 
-  hr = SetThreadDescription(GetCurrentThread(), namew);
+  hr = pSetThreadDescription(GetCurrentThread(), namew);
   uv__free(namew);
   if (FAILED(hr))
     return uv_translate_sys_error(HRESULT_CODE(hr));
@@ -312,6 +331,11 @@ int uv_thread_getname(uv_thread_t* tid, char* name, size_t size) {
   int r;
   DWORD exit_code;
 
+  uv_once(&uv__thread_name_once, uv__thread_name_init_once);
+
+  if (pGetThreadDescription == NULL)
+    return UV_ENOSYS;
+
   if (name == NULL || size == 0)
     return UV_EINVAL;
 
@@ -324,7 +348,7 @@ int uv_thread_getname(uv_thread_t* tid, char* name, size_t size) {
 
   namew = NULL;
   thread_name = NULL;
-  hr = GetThreadDescription(*tid, &namew);
+  hr = pGetThreadDescription(*tid, &namew);
   if (FAILED(hr))
     return uv_translate_sys_error(HRESULT_CODE(hr));
 

src/win/winapi.h

@@ -4828,13 +4828,4 @@ typedef int (WINAPI *uv_sGetHostNameW)
              int);
 extern uv_sGetHostNameW pGetHostNameW;
 
-/* processthreadsapi.h */
-#if defined(__MINGW32__)
-WINBASEAPI
-HRESULT WINAPI GetThreadDescription(HANDLE hThread,
-                                    PWSTR *ppszThreadDescription);
-WINBASEAPI
-HRESULT WINAPI SetThreadDescription(HANDLE hThread, PCWSTR lpThreadDescription);
-#endif
-
 #endif /* UV_WIN_WINAPI_H_ */