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SubjectRe: [patch 14/22] pollfs: pollable futex
On 5/2/07, Davi Arnaut <> wrote:
> It's quite easy to implement this scheme by write()ing the futexes all
> at once but that would break the one futex per fd association. For
> atomicity: if one of the futexes can't be queued, we would rollback
> (unqueue) the others.
> Sounds sane?

I don't know how you use "unqueue" in this context. If a queued futex
is one which is /locked/ by te call, then yes, this is the semantics
needed. Atomically locking a number of futexes means that if one of
the set cannot be locked all operations done to lock the others have
to be undone. It's an all-or-nothing situation.

Locking is not as easy as you might think, though. For non-PI futexes
there is deliberately no protocol in place describing what "locked"
means. The locking operation has to be customizable. This is what
the FUTEX_OP_* stuff is about.

And you wrote that currently each futex needs its own file descriptor.
So this would have to be changed, too.
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  Last update: 2007-05-02 18:49    [from the cache]
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