[Libguestfs] [PATCH 2/4] common/mltools: make sure machine readable output is flushed

[Pino Toscano]

On Monday, 25 March 2019 14:31:18 CET Richard W.M. Jones wrote:
> On Fri, Mar 22, 2019 at 04:33:41PM +0100, Pino Toscano wrote:
> > Enhance the helper printf function for machine readable output to always
> > flush after each string: this way, readers of the machine readable
> > stream can get the output as soon as it is outputted.
> > ---
> >  common/mltools/tools_utils.ml | 6 +++++-
> >  1 file changed, 5 insertions(+), 1 deletion(-)
> > 
> > diff --git a/common/mltools/tools_utils.ml b/common/mltools/tools_utils.ml
> > index 5a35708cd..ade4cb37f 100644
> > --- a/common/mltools/tools_utils.ml
> > +++ b/common/mltools/tools_utils.ml
> > @@ -59,7 +59,11 @@ let machine_readable () =
> >    | None -> None
> >    | Some chan ->
> >      let pr fs =
> > -      ksprintf (output_string chan) fs
> > +      let out s =
> > +        output_string chan s;
> > +        flush chan
> > +      in
> > +      ksprintf out fs
> >      in
> >      Some { pr }
> 
> I was looking to see if any of the existing calls to machine_readable
> are using %! (a format directive which causes the channel to be
> flushed).  I had expected there would be some, but my simple "git
> grep"s aren't turning up anything right now.

Yes, I know about %!, and that was my first attempt in patch 4, which
had:

    pr "%s\n%!" (JSON.string_of_doc ~fmt:JSON.Compact json)

However, it did not seem to work: the output seemed batched every 1/2
minutes or so, and even extra `pr "%!"` did not change anything.
Even when using Obj.magic, the fd still is not flushed immediately with
%!...

-- 
Pino Toscano
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