Re: fork() for microsoft windows (native but not Cygwin).

[Tatsuro MATSUOKA]

----- Original Message -----

> From: Tatsuro MATSUOKA 
> To: "octave-maintainers
> Cc: 
> Date: 2016/5/2, Mon 04:26
> Subject: fork() for microsoft windows (native but not Cygwin).
> 
> In the discussion for parallel octave-forge package:
> http://savannah.gnu.org/bugs/?41148
> 
> 
> It should be checked the implementation of fork() on windows.
> The native windows C compiler does not have a fork() function.
> 
> On octave prompt
> 
>>>  help fork
> 
> tells that fork() on octave implemented in libinterp/corefcn/syscalls.cc.
> 
> I looked into the code of syscalls.cc.
> (http://octave.org/doxygen/4.1/d7/dba/syscalls_8cc_source.html)
> 
> Around line 555,
> 
> 555   DEFUNX ("fork", Ffork, args, ,
> 556         "-*- texinfo -*-\n\
> <snip>
> {
> 
>   578   octave_value_list retval;
>   579 
>   580   retval(1) = std::string ();
>   581   retval(0) = -1;
>   582 
>   583   int nargin = args.length ();
>   584 
>   585   if (nargin == 0)
>   586     {
>   587       std::string msg;
>   588 
>   589       pid_t pid = octave_syscalls::fork (msg);
>   590 
>   591       retval(1) = msg;
>   592       retval(0) = pid;
>   593     }
>   594   else
>   595     print_usage ();
>   596 
>   597   return retval;
>   598 }
> 
> In oct-syscalls.cc
> (http://octave.org/doxygen/4.0/d5/d5e/oct-syscalls_8cc_source.html)
>   107 pid_t
>   108 octave_syscalls::fork (std::string& msg)
>   109 {
>   110   pid_t status = -1;
>   111 
>   112 #if defined (HAVE_FORK)
>   113   status = ::fork ();
>   114 
>   115   if (status < 0)
>   116     msg = gnulib::strerror (errno);
>   117 #else
>   118   msg = NOT_SUPPORTED ("fork");
>   119 #endif
>   120 
>   121   return status;
>   122 }
> 
> To my knowledge, fork() is not implemented in native windows.
> Cygwin implements fork() because cygwin offers almost all posix APIs.
> 
> The discussion resemble for pipe() on windows but native windows completely
> lacks the fork.  If we want to use fork on windows we should implement
> it using windows API that perhaps in done on the Cygwin


As reported an another post, I have been succeeded to build octave-4.0.2 
on native windows.

Thus I can check the config.log and config.h. 
(Of course I can see config.h in include/octave-4.0.2/octave from binary 
distribution.)


fork related parts of config.log
******************************************
configure:70184: checking for fork

configure:70184: gcc -o conftest.exe -g -O2 -pthread -fopenmp   conftest.c -lm  
 -lgdi32 -lws2_32 -luser32 -lkernel32 -lgdi32 -lws2_32 -luser32 -lkernel32 >&5
conftest.c:594:6: warning: conflicting types for built-in function 'fork'
 char fork ();
      ^
C:\Users\MATSUO~1\AppData\Local\Temp\ccQjF9mf.o: In function `main':
d:\usr\Tatsu\program\Octave\octaveBuild\4.0.2\build/conftest.c:605: undefined 
reference to `fork'
collect2.exe: error: ld returned 1 exit status
configure:70184: $? = 1
configure: failed program was:
| /* confdefs.h */
| #define PACKAGE_NAME "GNU Octave"
<snip a lot of define_s>
| #define HAVE_EXPM1F 1
| /* end confdefs.h.  */
| /* Define fork to an innocuous variant, in case <limits.h> declares fork.
|    For example, HP-UX 11i <limits.h> declares gettimeofday.  */
| #define fork innocuous_fork
| 
| /* System header to define __stub macros and hopefully few prototypes,
|     which can conflict with char fork (); below.
|     Prefer <limits.h> to <assert.h> if __STDC__ is defined, since
|     <limits.h> exists even on freestanding compilers.  */
| 
| #ifdef __STDC__
| # include <limits.h>
| #else
| # include <assert.h>
| #endif
| 
| #undef fork
| 
| /* Override any GCC internal prototype to avoid an error.
|    Use char because int might match the return type of a GCC
|    builtin and then its argument prototype would still apply.  */
| #ifdef __cplusplus
| extern "C"
| #endif
| char fork ();
| /* The GNU C library defines this for functions which it implements
|     to always fail with ENOSYS.  Some functions are actually named
|     something starting with __ and the normal name is an alias.  */
| #if defined __stub_fork || defined __stub___fork
| choke me
| #endif
| 
| int
| main ()
| {
| return fork ();
|   ;
|   return 0;
| }
configure:70184: result: no
******************************************

fork related part of config.h

*******************************************
/* Define to 1 if you have the `fork' function. */
/* #undef HAVE_FORK */
*******************************************


Apparently the fork is not recognized and HAVE_FORK is undefined.

The expected behavior fork to print fork is not supported in the current 
situation.

In think that this is a bug.

Is it better to register the phenomena to the bug tracker?

(I searched in the bug tracker by the keyword "fork" but cannot find topic that 
related fork() to windows.)


Tatsuro