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Date: Sun, 3 Mar 2024 22:45:14 -0800
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Subject: Re: Native posix_spawn() in Cygwin?
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From: Mark Geisert via Cygwin <cygwin@cygwin.com>
Reply-To: Mark Geisert <mark@maxrnd.com>
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On 3/3/2024 7:27 PM, Dan Shelton via Cygwin wrote:
> On Tue, 27 Feb 2024 at 07:34, <gs-cygwin.com@gluelogic.com> wrote:
>>
>> On Tue, Feb 27, 2024 at 06:54:42AM +0100, Dan Shelton via Cygwin wrote:
>>> On Tue, 27 Feb 2024 at 06:47, Brian Inglis via Cygwin <cygwin@cygwin.com> wrote:
>>>>
>>>> On 2024-02-26 20:23, Dan Shelton via Cygwin wrote:
>>>>> Does Cygwin implement a native, i.e. without form(),exec(), implementation of posix_spawn()?
>>>>
>>>> Check the API compatibility docs online:
>>>>
>>>>          https://cygwin.com/cygwin-api/compatibility.html#std-susv4
>>>>
>>>> or optional locally installed package cygwin-doc:
>>>>
>>>>          /usr/share/doc/cygwin-doc/html/cygwin-api/compatibility.html#std-susv4
>>>
>>> That document does not answer my question.
>>>
>>> I know posix_spawn() is there. But the question is: Does it use just
>>> Cygwin fork(),exec(), or the native Win32 spawn() api?
>>>
>>> Dan
>>> --
>>> Dan Shelton - Cluster Specialist Win/Lin/Bsd
>>
>> If you were going to make a small effort to answer the question
>> yourself, you could use strace, you could step through a debugger, or
>> you could check the source code.  Have you tried any of these?  What did
>> you find?  If you are unable to take any of those steps, why does
>> posix_spawn() matter to you?
> 
> strace does not help, as I need the Win32 calls BELOW posix_spawn(),
> to see the implementation details.

Check the source code, then. It's at:
     https://cygwin.com/cgit/newlib-cygwin/tree/winsup/cygwin/fork.cc

Look at line 587; there's the static function dofork(). Look at the
thirty or so lines above that; there's both fork() and 
__posix_spawn_fork() calling dofork(). So both those user-level
functions call into the exact same internals. (BTW __posix_spawn_fork() 
is called from posix_spawn(); the latter is in newlib and not Cygwin.)

You can even see the reason it's done this way by reading the comment.

..mark

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