win32: Rewrite late linking code (again) without using INIT_ONCE as groundwork

to backport r1866562 and 1859477 to APR 1.6.x and APR 1.7.x. It also slightly
improves performance and reduce lock contention.

* include/arch/win32/apr_arch_misc.h
  (apr_winapi_fpt_##fn): Declare as volatile and initialize to (ULONG_PTR) -1.
  (apr_winapi_ctrl_##fn, apr_winapi_init_once_##fn): Remove.
  (apr_winapi_ld_##fn): Concurrently invoke apr_load_dll_func() if
   apr_winapi_fpt_##fn == -1.

* misc/win32/misc.c
  (win32_late_dll_t.control): Remove.
  (win32_late_dll_t.dll_handle): Declare as volatile.
  (late_dll): Initialize dll_handle to INVALID_HANDLE_VALUE (assume that is
   invalid module handle).
  (apr_load_dll_func): Concurrently load library if dll_handle ==
   INVALID_HANDLE_VALUE. Then perform CAS and then free library if other
   thread performed initialization before.


git-svn-id: https://svn.apache.org/repos/asf/apr/apr/trunk@1871447 13f79535-47bb-0310-9956-ffa450edef68

1 files changed, 9 insertions, 14 deletions

diff --git a/include/arch/win32/apr_arch_misc.h b/include/arch/win32/apr_arch_misc.h
index 196914e68..387ea79f5 100644
--- a/include/arch/win32/apr_arch_misc.h
+++ b/include/arch/win32/apr_arch_misc.h
@@ -201,20 +201,15 @@ FARPROC apr_load_dll_func(apr_dlltoken_e fnLib, char *fnName, int ordinal);
  */
 #define APR_DECLARE_LATE_DLL_FUNC(lib, rettype, calltype, fn, ord, args, names) \
     typedef rettype (calltype *apr_winapi_fpt_##fn) args; \
-    static apr_winapi_fpt_##fn apr_winapi_pfn_##fn = NULL; \
-    static INIT_ONCE apr_winapi_ctrl_##fn = {INIT_ONCE_STATIC_INIT}; \
-    static BOOL WINAPI apr_winapi_init_once_##fn(PINIT_ONCE init_once,\
-                                                 PVOID baton, PVOID *context) \
-    { \
-        apr_winapi_pfn_##fn = (apr_winapi_fpt_##fn) \
-            apr_load_dll_func(lib, #fn, ord); \
-        return TRUE; \
-    } \
-static APR_INLINE int apr_winapi_ld_##fn(void) \
-    {   if (apr_winapi_pfn_##fn) return 1; \
-        InitOnceExecuteOnce(&apr_winapi_ctrl_##fn, apr_winapi_init_once_##fn, \
-                            NULL, NULL); \
-        if (apr_winapi_pfn_##fn) return 1; else return 0; }; \
+    static volatile apr_winapi_fpt_##fn apr_winapi_pfn_##fn = (PVOID) (ULONG_PTR) (-1); \
+    static APR_INLINE int apr_winapi_ld_##fn(void) \
+    {   \
+        apr_winapi_fpt_##fn cached_func = apr_winapi_pfn_##fn; \
+        if (cached_func == (PVOID) (ULONG_PTR) (-1)) { \
+            cached_func = (apr_winapi_fpt_##fn) apr_load_dll_func(lib, #fn, ord); \
+            InterlockedExchangePointer(&((PVOID)apr_winapi_pfn_##fn), cached_func); \
+        } \
+        if (cached_func) return 1; else return 0; }; \
     static APR_INLINE rettype apr_winapi_##fn args \
     {   if (apr_winapi_ld_##fn()) \
             return (*(apr_winapi_pfn_##fn)) names; \