On 1/8/14, 10:20 AM, Paul Gilmartin wrote:
On Wed, 8 Jan 2014 11:47:58 -0500, Farley, Peter x23353 wrote:
I have always felt that the parent-goes-away-leaving-the-child-running scenario
was the *ix substitution for what we can do with XCTL in z/OS systems.
Ummm... Not quite. *IX supports the scenario:
a) Parent runs for a while, then fork()s child.
b) Parent and child run concurrently and cooperatively for a while.
c) Parent-goes-away-leaving-the-child-running.
XCTL fails to support (b) because the parent goes away instantly.
ATTACH fails to support (c) because the child can't outlive the
parent. (But why not? Silly design. Perhaps none of the OS/360
designers were orphans, so the concept never occurred to them.)
In *IX, if the parent goes away, the grandparent adopts the child.
I believe init (pid 1) becomes the parent. It is not uncommon for a
process to fork a child process and then the child to fork a grandchild
after which the middle process exits leaving the grandchild under the
care of init. This relieves the original process from dealing with wait
or SIGCHLD at some later time. This was especially common when BSD and
SYSVR4 Unix behaved differently in this area.
Regards,
Henry
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