Re: Revised futex(2) man page for review

[Davidlohr Bueso <dave-h16yJtLeMjHk1uMJSBkQmQ@public.gmane.org>]

On Mon, 2015-07-27 at 13:10 +0200, Michael Kerrisk (man-pages) wrote:
> Hi David,
> 
> On 03/31/2015 04:45 PM, Davidlohr Bueso wrote:
> > On Sat, 2015-03-28 at 12:47 +0100, Peter Zijlstra wrote:
> > 
> >>        The condition is represented by the futex word, which is an address  in
> >>        memory  supplied to the futex() system call, and the value at this mem‐
> >>        ory location.  (While the virtual addresses for the same memory in sep‐
> >>        arate  processes  may  not be equal, the kernel maps them internally so
> >>        that the same memory mapped in different locations will correspond  for
> >>        futex() calls.)
> >>
> >>        When  executing  a futex operation that requests to block a thread, the
> >>        kernel will only block if the futex word has the value that the calling
> > 
> > Given the use of "word", you should probably state right away that
> > futexes are only 32bit.
> 
> So, I made the opening sentence here:
> 
>        The  condition  is  represented  by  the  futex word, which is an
>        address in memory supplied to the futex() system  call,  and  the
>        32-bit  value  at  this  memory  location. 
> 
> Okay?

I think we can still improve :)

I've re-read the whole first paragraphs, and have a few comments that
touch upon this specific wording. Lets see. You have:

>        The  futex()  system call provides a method for waiting until a certain
>        condition becomes true.  It is typically used as a  blocking  construct
>        in the context of shared-memory synchronization: The program implements
>        the majority of the synchronization in user  space,  and  uses  one  of
>        operations  of  the  system call when it is likely that it has to block
>        for a longer time until the condition becomes true.  The  program  uses
>        another  operation of the system call to wake anyone waiting for a par‐
>        ticular condition.

I've rephrased the next paragraph. How about adding this to follow?

       A futex is in essence a 32-bit user-space address. All futex operations and
       conditions are governed by this variable, from now on referred to as 'futex
       word'. As such, a futex is identified by the address in shared memory, which
       may or may not be shared between different processes. For virtual memory, the
       kernel will internally handle and resolve the later. This futex word, along
       with the value at its the memory location, are supplied to the futex() system
       call.

Feel free to reword however you think is better.

Thanks,
Davidlohr

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