However, the "it works like Unix" way is what the OP wants.

Actually, I disagree with your reading of the OP's question there. S/he asked for a cross platform solution to starting an asynchronous process.

Using fork and exec is one way of acheiving this, at least under unix, but it isn't the only way.

I realise that portability isn't an issue for you, but as it seems to be for the OP, then he might be better off using

system('command &'); on unix and

system('start command'); on Win32

And whatever the equivalent one-liner would be on his VMS systems, as the near-symmetry of the solutions on the different platforms would be much easier to manage than using the fork and exec model on unix and something different on the others.

The problem arises because of the need to try and emulate a perl behaviour that derives directly from a unix system behaviour that simply doesn't exist in the other platforms. AS have done a pretty good job of the emulation under Win32, and it works well enough for many purposes, but not all.

However, the lack of this unix feature in Win32 does not mean that Win32 is lacking the required facility--in this case the ability to start one asynchronous process from another--it just acheives it in a different, and one could say, more direct way.

Ie.

    CreateProcess(command, ASYNCH); # done
[download]

as opposed to

    newProc = CreateProcess();
    CopyDataSegs(thisProc, newProc);
    newProc(command);
    BlowAwayCode&Data();
    OverlayCodeFrom(command);
[download]

That doesn't mean its better or worse, just different. Hence the question about VMS and s390. Which of the two models do they more closely resemble? Or do they have a third model? How good is the fork and exec model supported on those platforms.

Using the system( 'start command' ); to start an asynchronous process actually comes down to remarkably similar set of steps as is used in the fork and exec model, and is neither hugely more or less efficient.

The problem arises because perl mirrors the underlying unix system calls so closely, which makes porting it to any non-unix system difficult.That's not a critisism of either unix nor perl. Just a statement of fact. Had unix had a createProcessAsynch() system call rather than relying on the fork and exec model, the porting problems to other systems would have been simpler.