This file was never truly necessary and has never actually been used in
the history of Tailscale's open source releases.
A Brief History of AUTHORS files
---
The AUTHORS file was a pattern developed at Google, originally for
Chromium, then adopted by Go and a bunch of other projects. The problem
was that Chromium originally had a copyright line only recognizing
Google as the copyright holder. Because Google (and most open source
projects) do not require copyright assignemnt for contributions, each
contributor maintains their copyright. Some large corporate contributors
then tried to add their own name to the copyright line in the LICENSE
file or in file headers. This quickly becomes unwieldy, and puts a
tremendous burden on anyone building on top of Chromium, since the
license requires that they keep all copyright lines intact.
The compromise was to create an AUTHORS file that would list all of the
copyright holders. The LICENSE file and source file headers would then
include that list by reference, listing the copyright holder as "The
Chromium Authors".
This also become cumbersome to simply keep the file up to date with a
high rate of new contributors. Plus it's not always obvious who the
copyright holder is. Sometimes it is the individual making the
contribution, but many times it may be their employer. There is no way
for the proejct maintainer to know.
Eventually, Google changed their policy to no longer recommend trying to
keep the AUTHORS file up to date proactively, and instead to only add to
it when requested: https://opensource.google/docs/releasing/authors.
They are also clear that:
> Adding contributors to the AUTHORS file is entirely within the
> project's discretion and has no implications for copyright ownership.
It was primarily added to appease a small number of large contributors
that insisted that they be recognized as copyright holders (which was
entirely their right to do). But it's not truly necessary, and not even
the most accurate way of identifying contributors and/or copyright
holders.
In practice, we've never added anyone to our AUTHORS file. It only lists
Tailscale, so it's not really serving any purpose. It also causes
confusion because Tailscalars put the "Tailscale Inc & AUTHORS" header
in other open source repos which don't actually have an AUTHORS file, so
it's ambiguous what that means.
Instead, we just acknowledge that the contributors to Tailscale (whoever
they are) are copyright holders for their individual contributions. We
also have the benefit of using the DCO (developercertificate.org) which
provides some additional certification of their right to make the
contribution.
The source file changes were purely mechanical with:
git ls-files | xargs sed -i -e 's/\(Tailscale Inc &\) AUTHORS/\1 contributors/g'
Updates #cleanup
Change-Id: Ia101a4a3005adb9118051b3416f5a64a4a45987d
Signed-off-by: Will Norris <will@tailscale.com>
Bounded DeliveredEvent queues reduce memory usage, but they can deadlock under load.
Two common scenarios trigger deadlocks when the number of events published in a short
period exceeds twice the queue capacity (there's a PublishedEvent queue of the same size):
- a subscriber tries to acquire the same mutex as held by a publisher, or
- a subscriber for A events publishes B events
Avoiding these scenarios is not practical and would limit eventbus usefulness and reduce its adoption,
pushing us back to callbacks and other legacy mechanisms. These deadlocks already occurred in customer
devices, dev machines, and tests. They also make it harder to identify and fix slow subscribers and similar
issues we have been seeing recently.
Choosing an arbitrary large fixed queue capacity would only mask the problem. A client running
on a sufficiently large and complex customer environment can exceed any meaningful constant limit,
since event volume depends on the number of peers and other factors. Behavior also changes
based on scheduling of publishers and subscribers by the Go runtime, OS, and hardware, as the issue
is essentially a race between publishers and subscribers. Additionally, on lower-end devices,
an unreasonably high constant capacity is practically the same as using unbounded queues.
Therefore, this PR changes the event queue implementation to be unbounded by default.
The PublishedEvent queue keeps its existing capacity of 16 items, while subscribers'
DeliveredEvent queues become unbounded.
This change fixes known deadlocks and makes the system stable under load,
at the cost of higher potential memory usage, including cases where a queue grows
during an event burst and does not shrink when load decreases.
Further improvements can be implemented in the future as needed.
Fixes#17973Fixes#18012
Signed-off-by: Nick Khyl <nickk@tailscale.com>
Will Norris
Nick Khyl
David Anderson