> * Why are we configuring an API behaviour via a global variable in
> 21st century?
I was mimicking how "ungroup" worked, but now that Avar mentions
that pattern was for a quick regression fix, I can fix it to pass it in as a
parameter.
> * The name "task_finished" is mentioned, but it is unclear what it
> is. Is it one of the parameters to run_process_parallel()?
It is one of the callback functions passed in as a parameter to
run_process_paraller(). I'll go ahead and clarify that.
> * Is the effect of the new feature that task_finished callback is
> called with the output, in addition to the normal output? I am
> not sure why it is called "pipe". The task_finished callback may
> be free to fork a child and send the received output from the
> task to that child over the pipe, but that is what a client code
> could do and is inappropriate to base the name of the mechanism,
> isn't it?
The output in task_finished callback, before pipe_output, either
contains part of the output or the entire output of the child process,
since the output is periodically collected into stderr and then reset.
The intention of output I believe is for the caller to be able to add
anything they would like to the end (this can be seen with functions
like fetch_finished() in builtin/fetch.c). My intention with pipe_output
is to guarantee that output contains the entire output of the child
process so task_finished can utilize it.
>
> > @@ -1770,10 +1771,12 @@ int run_processes_parallel(int n,
> > int output_timeout = 100;
> > int spawn_cap = 4;
> > int ungroup = run_processes_parallel_ungroup;
> > + int pipe_output = run_processes_parallel_pipe_output;
> > struct parallel_processes pp;
> >
> > /* unset for the next API user */
> > run_processes_parallel_ungroup = 0;
> > + run_processes_parallel_pipe_output = 0;
> >
> > pp_init(&pp, n, get_next_task, start_failure, task_finished, pp_cb,
> > ungroup);
> > @@ -1800,7 +1803,8 @@ int run_processes_parallel(int n,
> > pp.children[i].state = GIT_CP_WAIT_CLEANUP;
> > } else {
> > pp_buffer_stderr(&pp, output_timeout);
> > - pp_output(&pp);
> > + if (!pipe_output)
> > + pp_output(&pp);
>
> So, we do not send the output from the child to the regular output
> channel when pipe_output is in effect. OK.
>
> > }
> > code = pp_collect_finished(&pp);
> > if (code) {
>
> And no other code changes? This is quite different from what I
> expected from reading the proposed log message.
>
> Am I correct to say that under this new mode, we no longer flush any
> output while the child task is running (due to the change in the
> above hunk to omit calls to pp_output() during the run) and instead
> keep accumulating in the strbuf, until the child task finishes, at
> which time pp_collect_finished() will call task_finished callback.
>
> Even though the callback usually consumes the last piece of the
> output since the last pp_output() call made during the normal
> execution of the run_processes_parallel() loop, because we omitted
> these calls, we have full output from the child task accumulated in
> the children[].err strbuf. We may still not output .err for real,
> as we may not be the output_owner, in which case we may only append
> to .buffered_output member.
>
> I am puzzled simply because, if the above summary is correct, I do
> not see how a word "pipe" have a chance to come into the picture.
Ah I see what you mean here -- your summary is correct. Something
like "buffer_output" would make much more sense.
> I can sort of see that in this mode, we would end up buffering the
> entire output from each child task into one strbuf each, and can
> avoid stalling the child tasks waiting for their turn to see their
> output pipes drained. But is this a reasonable thing to do? How do
> we control the memory consumption to avoid having to spool unbounded
> amount of output from child tasks in core, or do we have a good
> reason to believe that we do not have to bother?
You are correct that storing unbounded output doesn't seem like a good
idea. One idea I have is to parse output during the periodic collection rather
than waiting till the end. The other idea I had was to add another
"git status --porcelain" option that would only output the necessary
pieces of information so we wouldn't have to bother with worrying about
unbounded output.
Any other thoughts as to how I can workaround this?
Thanks!
