[tor-dev] Upcoming Tor change with application impact: "Dormant Mode"

Mark Smith mcs at pearlcrescent.com
Thu Dec 20 14:50:43 UTC 2018

On 12/13/18 3:56 PM, Nick Mathewson wrote:
> ...
> In 0.4.0.x, Tor will begin supporting a new "dormant" mode in which it
> does not initiate network activity, and tries to avoid CPU wakeups.
> ...
> == Compatibility issues
> I see two issues here: one minor, and one major.
> Minor issue: some applications periodically make requests to the tor
> network on their own -- for example, Tor Browser's update requests.
> These requests prevent Tor from becoming dormant.  If this is
> undesired, we can add some way around this.

Tor Browser's update requests happen twice per day (and only for desktop
browsers). I am not 100% sure, but I don't think any other timer-based
requests occur more frequently in Tor Browser, so I don't think this
will cause too much activity.

> Major issue: some applications expect that Tor will always bootstrap
> when it starts, and delay presenting their own UI until Tor is ready.
> But if Tor starts as dormant, then it will not bootstrap until it
> receives a request from the client or a "SIGNAL ACTIVE"  command from
> the controller. This could lead to breakage as the application waits
> for Tor to tell it that it's ready, and Tor waits for somebody to tell
> it that it's needed.

Since most users will use their browser very soon after they start it,
for Tor Browser we will probably need to do "SIGNAL ACTIVE" each time
during startup.  For us it would be convenient if there was a way to do
that on the command line or equivalently via a torrc option.
> Are all application developers okay with the issues above, and okay
> with working around them?  If not, we may need changes in Tor before
> 0.4.0.x is released.  Let's talk!

I am sure I can find out somewhere, but what is the approximate schedule
for 0.4.0.x?


Mark Smith
Pearl Crescent

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