These timers behave better with non-monotonic clocks than our old
ones, and also try harder to make once-per-second events get called
one second apart, rather than one-plus-epsilon seconds apart.
This fixes bug 943 for everybody using Libevent 2.0 or later.
We need to ensure that we close timeout measurement circuits. While
we're at it, we should close really old circuits of certain types that
aren't in use, and log really old circuits of other types.
We need to record different statistics at point of timeout, vs the point
of forcible closing.
Also, give some better names to constants and state file variables
to indicate they are not dealing with timeouts, but abandoned circuits.
In rare cases, we could cannibalize a one-hop circuit, ending up
with a two-hop circuit. This circuit would not be actually used,
but we should prevent its creation in the first place.
Thanks to outofwords and swissknife for helping to analyse this.
Most of the changes here are switches to use APIs available on Windows
CE. The most pervasive change is that Windows CE only provides the
wide-character ("FooW") variants of most of the windows function, and
doesn't support the older ASCII verions at all.
This patch will require use of the wcecompat library to get working
versions of the posix-style fd-based file IO functions.
[commit message by nickm]
Back when we changed the idea of a connection being "too old" for new
circuits into the connection being "bad" for new circuits, we didn't
actually change the info messages. This led to telling the user that
we were labelling connections as "too old" for being worse than
connections that were actually older than them.
Found by Scott on or-talk.
There are now four ways that CBT can be disabled:
1. Network-wide, with the cbtdisabled consensus param.
2. Via config, with "LearnCircuitBuildTimeout 0"
3. Via config, with "AuthoritativeDirectory 1"
4. Via a state file write failure.
This should prevent some asserts and storage of incorrect build times
for the cases where Tor is suspended during a circuit construction, or
just after completing a circuit. The idea is that if the circuit
build time is much greater than we would have cut it off at, we probably
had a suspend event along this codepath, and we should discard the
value.
In case we decide that the timeout rate is now too high due to our
change of the max synthetic quantile value, this consensus parameter
will allow us to restore it to the previous value.
This is for the other issue we saw in Bug 1335. A large number of high
timeouts were causing the timeout calculation to slowly drift upwards,
especially in conditions of load. This fix repeatedly regenerates all of
our synthetic timeouts whenever the timeout changes, to try to prevent
drift.
It also lowers the timeout cap to help for some cases of Bug 1245, where
some timeout values were so large that we ended up allocating a ton of
scratch memory to count the histogram bins.
The downside is that lowering this cap is affecting our timeout rate.
Unfortunately, the buildtimeout quantile is now higher than the actual
completion rate by what appears to be about 7-10%, which probably
represents the skew in the distribution due to lowering this synthetic
cap.
In my state files, I was seeing several peaks, probably due to different
guards having different latency. This change is meant to better capture
this behavior and generate more reasonable timeouts when it happens. It
is improving the timeout values for my collection of state files.
