Re: [PATCH 2/4] transport-helper: check if remote helper is alive

> On Mon, Apr 01, 2013 at 03:46:42PM -0600, Felipe Contreras wrote:
>
>> Otherwise transport-helper will continue checking for refs and other
>> things what will confuse the user more.
>> [...]
>> diff --git a/transport-helper.c b/transport-helper.c
>> index cb3ef7d..dfdfa7a 100644
>> --- a/transport-helper.c
>> +++ b/transport-helper.c
>> @@ -460,6 +460,10 @@ static int fetch_with_import(struct transport *transport,
>>
>>       if (finish_command(&fastimport))
>>               die("Error while running fast-import");
>> +
>> +     if (!check_command(data->helper))
>> +             die("Error while running helper");
>> +
>>       argv_array_free_detached(fastimport.argv);
>
> Can you be more specific about what happens when we miss the death here,
> what happens next, etc?

> Checking asynchronously for death like this is subject to a rac
> condition; the helper may be about to die but not have died yet. In
> practice we may catch some cases, but this seems like an indication that
> the protocol is not well thought-out. Usually we would wait for a
> confirmation over the read pipe from a child, and know that the child
> failed when either:
>
>   1. It tells us so on the pipe.
>
>   2. The pipe closes (at which point we know it is time to reap the
>      child).
>
> Why doesn't that scheme work here? I am not doubting you that it does
> not; the import helper protocol is a bit of a mess, and I can easily
> believe it has such a problem. But I'm wondering if it's possible to
> improve it in a more robust way.