Discussion turned out a warning is not enough, but we need to die in case
of blocking output as we can lockup the child processes.
Junio wrote:
> Imagine that we are running two things A and B at the same time. We
> ask poll(2) and it says both A and B have some data ready to be
> read, and we try to read from A. strbuf_read_once() would try to
> read up to 8K, relying on the fact that you earlier set the IO to be
> nonblock. It will get stuck reading from A without allowing output
> from B to drain. B's write may get stuck because we are not reading
> from it, and would cause B to stop making progress.
> What if the other sides of the connection from A and B are talking
> with each other, and B's non-progress caused the processing for A on
> the other side of the connection to block, causing it not to produce
> more output to allow us to make progress reading from A (so that
> eventually we can give B a chance to drain its output)? Imagine A
> and B are pushes to the same remote, B may be pushing a change to a
> submodule while A may be pushing a matching change to its
> superproject, and the server may be trying to make sure that the
> submodule update completes and updates the ref before making the
> superproject's tree that binds that updated submodule's commit
> availble, for example? Can we make any progress from that point?
Signed-off-by: Stefan Beller <sbel...@google.com>
---
run-command.c | 10 ++++------
1 file changed, 4 insertions(+), 6 deletions(-)
diff --git a/run-command.c b/run-command.c
index 0a3c24e..86fbe50 100644
--- a/run-command.c
+++ b/run-command.c
@@ -1006,15 +1006,13 @@ static void pp_cleanup(struct parallel_processes *pp)
sigchain_pop_common();
}
-static void set_nonblocking(int fd)
+static void set_nonblocking_or_die(int fd)
{
int flags = fcntl(fd, F_GETFL);
if (flags < 0)
- warning("Could not get file status flags, "
- "output will be degraded");
+ die("Could not get file status flags");
else if (fcntl(fd, F_SETFL, flags | O_NONBLOCK))
- warning("Could not set file status flags, "
- "output will be degraded");
+ die("Could not set file status flags");
}
/* returns
@@ -1052,7 +1050,7 @@ static int pp_start_one(struct parallel_processes *pp)
return code ? -1 : 1;
}
- set_nonblocking(pp->children[i].process.err);
+ set_nonblocking_or_die(pp->children[i].process.err);
pp->nr_processes++;
pp->children[i].in_use = 1;
--
2.6.1.247.ge8f2a41.dirty
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