[PATCH 1 of 4 V2] util: add a simple poll utility

[Adrian Buehlmann]

On 2015-06-04 03:57, Pierre-Yves David wrote:
> # HG changeset patch
> # User Pierre-Yves David <pierre-yves.david at fb.com>
> # Date 1432162805 18000
> #      Wed May 20 18:00:05 2015 -0500
> # Node ID 9d7dc60dc701d327ddda449e7455e85513d5df5b
> # Parent  443d4635e630cf5603afb6ba4bfcf6a0d68cd7a6
> util: add a simple poll utility
> 
> We'll use it to detect when a sshpeer have server output to be displayed.
> 
> The implementation is super basic because all case support is not the focus of
> this series.
> 
> diff --git a/mercurial/posix.py b/mercurial/posix.py
> --- a/mercurial/posix.py
> +++ b/mercurial/posix.py
..
> diff --git a/mercurial/windows.py b/mercurial/windows.py
> --- a/mercurial/windows.py
> +++ b/mercurial/windows.py
> @@ -369,10 +369,20 @@ def statislink(st):
>  
>  def statisexec(st):
>      '''check whether a stat result is an executable file'''
>      return False
>  
> +def poll(fds):
> +    """block until something happened on any filedescriptors

I think you can drop the rest of the doc string. Or perhaps instead
refer to posix module (in order to avoid comment duplication).

> +
> +    This is a generic helper that will check for any activity
> +    (read, write.  exception). return the list of touched file.
> +
> +    In unsupported case raise a NotImplementedError"""

..

> +    if os.name == 'nt': # we do not support windows yet.
> +        raise NotImplementedError()
> +

os.name is always 'nt' inside this module, so this can be simplified to:

       raise NotImplementedError()

(Nitpick: I think the comment ("we do not support windows yet.") is
unneeded. If you want to keep it: The correct name of that OS is 'Windows')

>  def readpipe(pipe):
>      """Read all available data from a pipe."""
>      chunks = []
>      while True:
>          size = win32.peekpipe(pipe)