On Wed, Apr 20, 2016 at 8:01 AM, David Turner <dturner@xxxxxxxxxxxxxxxx> wrote:
> On Wed, 2016-04-20 at 07:15 +0700, Duy Nguyen wrote:
>> Continuing my comment from the --use-watchman patch about watchman
>> not
>> being supported...
>>
>> On Wed, Apr 20, 2016 at 6:28 AM, David Turner <
>> dturner@xxxxxxxxxxxxxxxx> wrote:
>> > +static int poke_and_wait_for_reply(int fd)
>> > +{
>> > + struct strbuf buf = STRBUF_INIT;
>> > + struct strbuf reply = STRBUF_INIT;
>> > + int ret = -1;
>> > + fd_set fds;
>> > + struct timeval timeout;
>> > +
>> > + timeout.tv_usec = 0;
>> > + timeout.tv_sec = 1;
>> > +
>> > + if (fd < 0)
>> > + return -1;
>> > +
>> > + strbuf_addf(&buf, "poke %d", getpid());
>> > + if (write_in_full(fd, buf.buf, buf.len + 1) != buf.len + 1)
>> > + goto done_poke;
>> > +
>> > + /* Now wait for a reply */
>> > + FD_ZERO(&fds);
>> > + FD_SET(fd, &fds);
>> > + if (select(fd + 1, &fds, NULL, NULL, &timeout) == 0)
>> > + /* No reply, giving up */
>> > + goto done_poke;
>> > +
>> > + if (strbuf_getwholeline_fd(&reply, fd, 0))
>> > + goto done_poke;
>> > +
>> > + if (!starts_with(reply.buf, "OK"))
>> > + goto done_poke;
>>
>> ... while we could simply check USE_WATCHMAN macro and reject in
>> update-index, a better solution is sending "poke %d watchman" and
>> returning "OK watchman" (vs "OK") when watchman is supported and
>> active. If the user already requests watchman and index-helper
>> returns
>> just "OK" then we can warn the user the reason of possible
>> performance
>> degradation. It's related to the error reporting, but I don't think
>> you can send straight errors over unix socket. It's possible but it's
>> a bit more complicated.
>
> Do you mean that we should do this here? Or in update-index -
> -watchman? If the former, I agree. If the latter, I'm not sure; maybe
> you'll be setting up your index before you've started the index helper?
Here is better than update-index because we can't know what
index-helper is capable of (the USE_WATCHMAN macro is more like a
suggestion)
>> > +static void refresh_by_watchman(struct index_state *istate)
>> > +{
>> > + void *shm = NULL;
>> > + int length;
>> > + int i;
>> > + struct stat st;
>> > + int fd = -1;
>> > + const char *path = git_path("shm-watchman-%s-%"PRIuMAX,
>> > + sha1_to_hex(istate->sha1),
>> > + (uintmax_t)getpid());
>> > +
>> > + fd = open(path, O_RDONLY);
>> > + if (fd < 0)
>> > + return;
>> > +
>> > + /*
>> > + * This watchman data is just for us -- no need to keep it
>> > + * around once we've got it open.
>> > + */
>> > + unlink(path);
>>
>> This will not play well when multiple processes read and refresh the
>> index at the same time.
>
> Multiple processes will have different pids, right? And the pid is
> included in the filename. Am I missing something?
Ahhh! I thought that pid was index-helper's. Silly me.
>> Now that I think of it, with watchman backing us, we probably should
>> just do nothing in update_index_if_able() (or write_locked_index()
>> when we know only stat info is changed) when watchman is active. The
>> purpose of update_index_if_able() is to avoid costly refresh, but we
>> can already avoid that with watchman. And updating big index files is
>> always costly (even though it should cost less with split-index).
>
> That sounds like a change we could make in a separate series. It's not
> a bad idea, but if our goal is to get the basic version out, we should
> start there.
Agreed. More optimizations can always wait till later. We just need a
good foundation first.
--
Duy
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