[PATCH] Allow usage of union wait for wait() functions and macros

[Christian Franke]

Christopher Faylor wrote:
> On Wed, Oct 05, 2011 at 11:17:58PM +0200, Christian Franke wrote:
>> Christopher Faylor wrote:
>>> On Wed, Oct 05, 2011 at 12:57:44PM +0200, Christian Franke wrote:
>>>> ...
>>>> diff --git a/winsup/cygwin/include/cygwin/wait.h b/winsup/cygwin/include/cygwin/wait.h
>>>> index bed81b7..e4edba2 100644
>>>> --- a/winsup/cygwin/include/cygwin/wait.h
>>>> +++ b/winsup/cygwin/include/cygwin/wait.h
>>>> @@ -1,6 +1,6 @@
>>>> /* cygwin/wait.h
>>>>
>>>> -   Copyright 2006, 2009 Red Hat, Inc.
>>>> +   Copyright 2006, 2009, 2011 Red Hat, Inc.
>>>>
>>>> This file is part of Cygwin.
>>>>
>>>> @@ -16,6 +16,9 @@ details. */
>>>> #define WCONTINUED 8
>>>> #define __W_CONTINUED	0xffff
>>>>
>>>> +/* Will be redefined in sys/wait.h.  */
>>>> +#define __wait_status_to_int(w)  (w)
>>>> +
>>> Why is this necessary?  It doesn't look like it is ever expanded in cygwin/wait.h.
>> This would be needed if cygwin/wait.h is included separately without
>> sys/wait.h
>> (e.g. stdlib.h ->  cygwin/stdlib.h ->  cygwin/wait.h)
>> and some W*() macro is actually used.
>>
>>
>>> If a redefinition is necessary why not put it all in one place?
>> The W*() macros and union wait are closely related. So a probably better
>> approach would be to move union wait to cygwin/wait.h and define
>> __wait_status_to_int() only there.
>>
>> But then C++ compile may fail because cygwin/wait.h is sometimes
>> included indirectly inside an extern "C" block:
>> w32api/shlobj.h ->  extern "C" { w32api/ole2.h ...->  stdlib.h ...->
>> cygwin/wait.h }
> Ok.  I see that Linux's use of similar macros is convoluted too.
> I really would rather keep this all together but I guess it isn't
> possible without redesigning stdlib.h and */wait.h.

Linux uses the following approach for the C++ case:

typedef void *__wait_status_ptr_t;
#define __wait_status_to_int(w)  (*(int*)&(w))

This prevents the C++ inline function problem but is not typesafe at all.

Meantime I found out that the inline functions can be used even if a 
file is included in an extern "C" block. It is possible to nest another 
extern "C++" block:

// w32api/shlobj.h:
extern "C" {
#include ...
   ...
   // cygwin/wait.h:
   ...
   #ifdef __cplusplus
   extern "C++" {
   inline int __wait_status_to_int(int __status) { .... }
   inline int __wait_status_to_int(const union wait &__status) { .... }
   }
   #endif

}

So it would be possible to move union wait and related functions to 
cygwin/wait.h. Possible new problem: This pollutes the stdlib.h 
namespace with 'union wait' and '#define w_termsig' etc..


>>> Also since Cygwin is C++ why do you need the __INSIDE_CYGWIN__ here?
>> There are still ten *.c files in winsup/cygwin :-)
> % cd winsup/cygwin
> % grep wait.h **/*.c
> %

OK, __INSIDE_CYGWIN__ is not needed here in practice (but possibly in 
theory :-)

Would the patch with __INSIDE_CYGWIN__ removed be GTG?

Christian