Re: [PATCH] tests: allow non-inotify tailf to keep up

["Pádraig Brady" <P@draigBrady.com>]

On 07/26/2014 09:44 PM, Andreas Henriksson wrote:
> When tailf is not using inotify, it seems to sleep for 0.25s between
> checks. Just giving a 0.1s time window between update and removal of the
> input file thus gives little chance for tailf to succeed.
> Similar between startup and append to file, make sure initial
> content is read before appending additional data by bumping the time.
> 
> This should possibly be bumped much larger to make sure that
> the tailf process actually gets a chance to run at all in the
> given time window. Otherwise it might fail on really slow/overloaded
> machines.
> The drawback would then ofcourse be to increase the time it takes
> to run the testsuite.
> 
> Signed-off-by: Andreas Henriksson <andreas@fatal.se>
> ---
>  tests/ts/tailf/simple | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/tests/ts/tailf/simple b/tests/ts/tailf/simple
> index 955844d..d0a1c5c 100755
> --- a/tests/ts/tailf/simple
> +++ b/tests/ts/tailf/simple
> @@ -27,9 +27,9 @@ echo {a..z} > $INPUT
>  
>  $TS_CMD_TAILF $INPUT > $TS_OUTPUT 2>&1 &
>  
> -sleep 0.1
> +sleep 0.5
>  echo {0..9} >> $INPUT
> -sleep 0.1
> +sleep 0.5
>  
>  rm -f $INPUT

For such tests coreutils uses a helper function
to apply a truncated exponential backoff,
to run quickly in the common case, but also
delay longer if necessary. See retry_delay_() at:

http://git.sv.gnu.org/gitweb/?p=coreutils.git;a=blob;f=init.cfg;h=725ee121;hb=HEAD#l608

cheers,
Pádraig.