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

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
(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) { .... }


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?


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