Notify systemd of ShutdownWaitLength

[Hello71]

No description provided.

[teor2345]

This code will be easier to read if it uses TOR_USEC_PER_SEC.
It might also be worth adding a comment to explain the extra time.

[coveralls]

Pull Request Test Coverage Report for Build 2792

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 2664 unchanged lines in 13 files lost coverage.
• Overall coverage increased (+0.02%) to 62.053%

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Files with Coverage Reduction	New Missed Lines	%
src/lib/thread/compat_pthreads.c	4	91.78%
src/feature/dirparse/authcert_parse.c	18	68.93%
src/feature/dircache/consdiffmgr.c	63	90.09%
src/feature/dircache/dirserv.c	67	63.96%
src/feature/nodelist/authcert.c	122	28.07%
src/feature/nodelist/nodelist.c	127	61.42%
src/feature/dircache/dircache.c	132	69.83%
src/feature/relay/dns.c	155	17.89%
src/feature/dirparse/ns_parse.c	197	67.97%
src/feature/dirclient/dirclient.c	222	18.44%

Totals
Change from base Build 2687:	0.02%
Covered Lines:	44125
Relevant Lines:	71109

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💛 - Coveralls

[teor2345]

Looks good, needs a few tweaks.

I'm also not sure why tor needs an extra 30 seconds to shut down.

[teor2345]

ShutdownWaitLength is an int. To avoid (a very unlikely) overflow on addition, use:

Suggested change

	(uint64_t)(options->ShutdownWaitLength + 30) * TOR_USEC_PER_SEC);
	((uint64_t)(options->ShutdownWaitLength) + 30) * TOR_USEC_PER_SEC);

[teor2345]

I am not sure why you are giving tor an extra 30 seconds beyond the shutdown wait length to shut down:
https://www.freedesktop.org/software/systemd/man/systemd.service.html#TimeoutStopSec=

1s or 2s seems like a reasonable time for tor to run its event loop and exit, but 30s might make relay operators think that their device has hung.

[Hello71]

I made it a very conservative number because I don't know how long tor might actually take, and because the default is 90 seconds. In fact, it might make more sense to use 90, because that's the default, and ShutdownWaitLength is a sort of "added time". Also note that systemd won't wait around forever like an idiot; as long as tor actually exits before this time the shutdown process will continue immediately. The only difference is that if tor actually fails to exit for some reason then systemd will wait for 30 seconds longer. Also, this won't do anything with the default configurations for ShutdownWaitLength and DefaultTimeoutStopSec, because tor will tell systemd to wait for 30+30=60 seconds, but systemd will wait min(60, DefaultTimeoutStopSec=90)=90 seconds.

[Hello71]

For future reference, I think you should've opened two separate comments here (I think that's possible...).

[Hello71]

Oh, I remember why I increased this from my first revision: I wanted to consider the case where tor may in fact take an extra few tens of seconds to clean up, which is not entirely absurd, like if we try to free memory that was actually swapped out because it was used at startup and then never again.

[teor2345]

I made it a very conservative number because I don't know how long tor might actually take, and because the default is 90 seconds. In fact, it might make more sense to use 90, because that's the default, and ShutdownWaitLength is a sort of "added time". Also note that systemd won't wait around forever like an idiot; as long as tor actually exits before this time the shutdown process will continue immediately. The only difference is that if tor actually fails to exit for some reason then systemd will wait for 30 seconds longer. Also, this won't do anything with the default configurations for ShutdownWaitLength and DefaultTimeoutStopSec, because tor will tell systemd to wait for 30+30=60 seconds, but systemd will wait min(60, DefaultTimeoutStopSec=90)=90 seconds.

I understand now. Please add a comment that explains the systemd default of 90 seconds.

[teor2345]

The Tor default is actually 30s:
https://github.com/torproject/tor/blob/master/contrib/dist/tor.service.in

Suggested change

	- Notify systemd of ShutdownWaitLength so it can be set to more than 90
	- Notify systemd of ShutdownWaitLength so it can be set to more than 30

[Hello71]

Yes, but the systemd default is 90.

[teor2345]

The default in the tor systemd config is 30 seconds. This overrides the systemd default. So on distributions that use the tor systemd config, this patch is required to extend ShutdownWaitLength beyond 30 seconds.

To avoid relay operator confusion, let's use the lower figure.

[Hello71]

Hm... to be honest I'm not sure how the default TimeoutSec works. It seems to me like if tor waits 30 seconds, and then does some non-zero work, then it should always be killed by systemd, assuming that systemd is not overly busy.