Re: CLONE_DETACHED and exit notification (was user-vm-unlock-2.5.31-A2)

From: Ingo Molnar (
Date: Fri Aug 16 2002 - 12:12:45 EST

On Fri, 16 Aug 2002, Jamie Lokier wrote:

> There's no "lock-counter format", because this isn't a lock -- it's a
> wakeup. There no need for atomicity either, because the listener only
> reads, it doesn't write.

well, technically a 'wait until value is 0' thing is of course a counter
format ...

> Here's a synchronous thread_join-style waiter; it is architecture-neutral:
> while (tid = *tid_address) != 0)
> retval = sys_futex (tid_address, FUTEX_WAIT, tid, 0);

yes, this would work. And the current method of setting the counter to 0
is arbitrary (and has a 'format') already, so there's no reason we couldnt
say that the TID cannot be used as a thread-join futex that is zeroed out
by CLONE_CLEARTID, and any (potential) waiters are woken up.

i'll try this and send a patch, it's a nice optimization.


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