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

[Tatsuro MATSUOKA]

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

> From:  
> To: "octave-maintainers" <octave-maintainers>
> Cc: 
> Date: 2016/5/2, Mon 07:09
> Subject: Re: fork() for microsoft windows (native but not Cygwin).
> 
> --- tmacchant wrote:
>>  > 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?
>> 
> I don't see the octave manual and explanation of spawnvp.  The spawnvp is 
> not able to use for the octave fork().
> 
> We have to write it using windows api like popen2 on octave for windows.
> 
> Tatsuro



Perhaps this is the start to implement fork() on windows.
https://www.cygwin.com/faq.html#faq.api.fork


One need to look the code how the Cygwin actually implement the fork().

Tatsuro