> Just came across a really thorny problem with our implementation of
> qmail-queue.
Is this a new bug?
> Basic summary is that we have a potential race condition between calls
> to waitpid() in the parent process and in qmail-queue. If the parent
> process' waitpid(-1) call enters before the child processes
> waitpid($child) does then the parent ends up collecting the zombie,
> and the child never sees the qmail-queue exiting, and thus hangs
> indefinitely.
>
> Anyone have any thoughts on how to solve this? Can you tell waitpid()
> to only operate on child processes and not grandchild processes?
No, but you can tell it to only wait for a specific pid. But that
won't help in this case.
I don't remember waitpid ever detecting grandchild processes. It
shouldn't be.
The value of pid can be one of:
< -1 which means to wait for any child process whose process group
ID is equal to the absolute value of pid.
-1 which means to wait for any child process; this is the same
behaviour which wait exhibits.
0 which means to wait for any child process whose process group
ID is equal to that of the calling process.
> 0 which means to wait for the child whose process ID is equal to
the value of pid.
