Re: Design mixed 32 and 64 bit systems.

[Christopher Faylor <cgf-use-the-mailinglist-please at cygwin dot com>]

On Mon, Dec 02, 2013 at 01:30:29PM -0700, Warren Young wrote:
>On 12/2/2013 12:56, Christopher Faylor wrote:
>> On Mon, Dec 02, 2013 at 12:35:00PM -0700, Warren Young wrote:
>>> This happens because POSIX PIDs are in a table that lives in
>>> cygwin1.dll's memory space, and because there are two DLLs, there are
>>> two different PID tables.
>>
>> Actually POSIX pids are Windows PIDs.  The distinction becomes fuzzy
>> after an exec, though, where the Cygwin PID continues to be the PID
>> of the process which previously exec'ed it.
>
>Of the four PID values this pair of programs prints, shouldn't at least 
>two should be the same, then?  I get four different values here:
>
>PARENT: My PID is 5048; created child PID 5684
>CHILD:  My PID is 3108; my parent's PID is 1.

The parent pid *is* a cygwin invention (although technically it doesn't
have to be).  When executed between different architectures you lose the
parent/child linkage, since as you say, the DLL in the execed process
thinks it's being started from a non-cygwin windows program.

It's a subtle distinction but there is no real table of Cygwin pids
maintained by the DLL.  Each process has a shared memory region
associated with it that holds information like the parent pid.  This
shared memory region is not recognized between x86/x86_64.

cgf