wait* status definition

[Ulrich Drepper <drepper@xxxxxxxxxx>]

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I got asked a question to which I cannot give a definitive answer.


Assume process A waits for process B (waitpid, waitid, ...)

Process B is stopped (by itself or a third process)

Process A wakes up and is signalled WIFSTOPPED

Now process A calls wait* again.


What is this call supposed to do?  There are two possible
interpretations of the standard:

- - status information is the change from running to stopped.  This
  information has been communicated in the first wait* call and
  therefore the second call will block

- - the status of the child is still stopped and therefore the call
  will immediately return and signal WIFSTOPPED again


I think the former is right and the next status to return is
WIFCONTINUED.  Why else should there by WIFCONTINUED.

But:

- - WIFCONTINUED is an XSI option

- - the exact description for WIFSTOPPED is

           True if child is currently stopped

  This seems to imply that the state information is sticky and should
  be re-reported.


I guess the final answer depends on historic practice.  Linux does the
latter, it returns immediately.


- --
➧ Ulrich Drepper ➧ Red Hat, Inc. ➧ 444 Castro St ➧ Mountain View, CA ❖
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