On Mon, Sep 14, 2015 at 09:46:58AM -0700, Stefan Beller wrote:
> I tried implementing a buffering solution for both stdout and stderr,
> but that doesn't really workout well if you consider interleaved output
> on the pipes as we cannot accurately replay that later on. To do that
> we would need to store the timing information of the channels, at least
> the relative order of it like:
>
> (stdout, First comes text to stdout),
> (stderr, interrupted by text in stderr)
> (stdout, but stdout doesn't bother, blasting more text)
> (stderr, continues to interrupt)
>
> obtaining the information is inherently racy, as all we can do is
> polling/reading from both stdout/err as fast as possible but without
> proper synchronization mechanisms we cannot be sure.
I don't think you need exact timing information. This is no different
than running the commands themselves, with stdout and stderr writing to
a pty that your terminal emulator will then read() from. If the program
produces intermingled stdout/stderr that clogs up the terminal, that is
its problem.
The only difference is that we're going to save it and later replay it
all very quickly. So I think it would be sufficient just to retain the
original order.
> I will add documentation explaining why the async output case
> will only deal with one channel. I chose stderr as that's already
> available and needed in this use case.
I suspect you could just set child->stdout_to_stderr in this case, and
then you get your ordering for free. But probably in the general case
people would want to run inspection commands that produce a useful
stdout.
To handle multiple channels, I think you could just do a linked list of
buffers rather than a single strbuf. Like:
struct io_chunk {
int channel;
char *buf;
size_t len;
struct io_chunk *next;
};
and just keep appending chunks to the list (and to dump them, just walk
the list, writing each to the appropriate channel descriptor).
-Peff
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