I don't think it's contrived --- writing not a byte, but the pid and
return status of the dead child to a pipe is an old but useful trick.
It gives a natural serialisation of child deaths, and also eliminates
the common race where a child dies before its parent has recorded its
pid in a data structure. See it as a safe way of converting an
asynchronous signal to a queued event.
Using pipes to wake up blocking select()s is a useful thing in general,
and often a lot cleaner than using signals when dealing with threads.
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