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

[Tatsuro MATSUOKA]

> 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
> 
> Am I wrong?
> 
> Tatsuro


In the gnulib manual,"9.287 fork"
https://www.gnu.org/software/gnulib/manual/html_node/fork.html


On Windows platforms (excluding Cygwin), this function is not implemented; use 
spawnvp instead.


Can octave fork() be implemented by spawnvp but not by fork on windows?

Tatsuro