Re: Design mixed 32 and 64 bit systems.

[Warren Young <warren@etr-usa.com>]

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On 12/2/2013 13:30, 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.

I've modified the test programs a bit.  The parent can launch either a 
32- or 64-bit child, and I've modified the two processes' output so 
they're easier to distinguish.

Run without args, parent64 still runs child32, but you can now pass "64" 
(i.e. "./parent64 64") to make it run the new child64 program.  When you 
do that, the output is completely sensible, unlike with the mixed 
bitness case:

     PARENT64: My PID is 8808; created child PID 3480.
     CHILD64:  My PID is 3480; my parent's PID is 8808.

Also, doesn't the fact that procps only shows processes running under 
the current Cygwin DLL indicate that the process table is DLL-specific?

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#include <iostream>
#include <unistd.h>

int main()
{
	std::cout << "CHILD32:  My PID is " << getpid() <<
			"; my parent's PID is " << getppid() << '.' << std::endl;
}

[-- Attachment #3: child64.cpp --]
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#include <iostream>
#include <unistd.h>

int main()
{
	std::cout << "CHILD64:  My PID is " << getpid() <<
			"; my parent's PID is " << getppid() << '.' << std::endl;
}

[-- Attachment #4: parent64.cpp --]
[-- Type: text/x-c++src, Size: 584 bytes --]

#include <iostream>

#include <unistd.h>

#include <errno.h>
#include <string.h>

int main(int argc, char* argv[])
{
	std::cout << "PARENT64: My PID is " << getpid() << "; " << std::flush;

	switch (int pid = fork()) {
		case -1:			// error
			std::cout << "ERROR: " << strerror(errno) << std::endl;
			break;

		case 0: {			// child
			const char* cmd = 
					(argc > 1 && strcmp(argv[1], "64") == 0) ?
					"./child64" :
					"./child32";
			execl(cmd, cmd, 0);
			break;
		}

		default:			// parent
			std::cout << "created child PID " << pid << '.' << std::endl;
	}

	sleep(1);
}