Fflush(stdout) doesn't work as expected.

[WSaffery]

Fflush(stdout) doesn't work as expected.

[ggouaillardet]

FWIW the issue does not occur with Open MPI v4.1.x
@rhc54 that suggests prrte (unless PMIx does all/most of the work) is involved here.

[rhc54]

Most likely in PMIx (src/common/pmix_iof.c) as it does the actual output. This is one of those "you cannot win" scenarios. Some users complain if the output comes in incomplete lines because of the inevitable interleaving that occurs, while others complain about this scenario. ORTE opted for one side, PMIx/PRRTE for the other. 🤷‍♂️

There is no way for us to know that someone called "fflush", so I'm not sure how one can resolve it. However, I'm happy to consider a PR that attempts to resolve it. I personally won't have time to look into better solutions before late this year (retirement is busy).

[ggouaillardet]

@rhc54 thanks for the quick reply, as far as I am concerned, I am fine with "it's not a bug, it's a feature" since I believe apps should either read from the command line or an input file, and not from stdin

[rhc54]

I suppose you could add a cmd line option to permit interleaving so that someone who needs/wants to output partial lines can do so. I have no issues with it - you'd just need to pass that down to PMIx so it doesn't buffer output.