This new facility will be used by future CLs in this series.

Change the only blocking call to netpoll to do the right thing when
netpoll returns an empty list.

Updates #6239
Updates #27707

Change-Id: I58b3c2903eda61a3698b1a4729ed0e81382bb1ed
Reviewed-on: https://go-review.googlesource.com/c/go/+/171821
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
Reviewed-by: Emmanuel Odeke <emm.odeke@gmail.com>

Add support to the main scheduler loop for handling timers on P's.
This is not used yet, as timers are not yet put on P's.

Updates #6239
Updates #27707

Change-Id: I6a359df408629f333a9232142ce19e8be8496dae
Reviewed-on: https://go-review.googlesource.com/c/go/+/171826
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Michael Knyszek <mknyszek@google.com>

When we put timers on P's, the wasm code will not be able to rely on
the timer goroutine. Use the beforeIdle hook to schedule a wakeup.

Updates #6239
Updates #27707

Change-Id: Idf6309944778b8c3d7178f5d09431940843ea233
Reviewed-on: https://go-review.googlesource.com/c/go/+/171827
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
Reviewed-by: Emmanuel Odeke <emm.odeke@gmail.com>

Updates #6239
Updates #27707

Change-Id: I52cab8bf3dc8c552463725fc1d9e4e6b12230b03
Reviewed-on: https://go-review.googlesource.com/c/go/+/171828
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Michael Knyszek <mknyszek@google.com>

Add new fields to runtime.timer, and adjust the various timer
functions in preparation for adding timers to P's. This continues to
use the old timer code.

Updates #6239
Updates #27707

Change-Id: I9adb3814f657e083ec5e22736c4b5b52b77b6a3f
Reviewed-on: https://go-review.googlesource.com/c/go/+/171829
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Michael Knyszek <mknyszek@google.com>

This fixes the Plan 9 support for the new timer code.

Updates #6239
Updates #27707

Change-Id: Ia498c399b8924910b97fcde07545fae3588aad47
Reviewed-on: https://go-review.googlesource.com/c/go/+/204045
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Michael Knyszek <mknyszek@google.com>

Updates #6239
Updates #27707

Change-Id: I0a62c1374db485dd830bf02e59625997d9247fc3
Reviewed-on: https://go-review.googlesource.com/c/go/+/203890
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

No big changes in the runtime package benchmarks.

Changes in the time package benchmarks:

name                      old time/op  new time/op  delta
AfterFunc-12              1.57ms ± 1%  0.07ms ± 1%  -95.42%  (p=0.000 n=10+8)
After-12                  1.63ms ± 3%  0.11ms ± 1%  -93.54%  (p=0.000 n=9+10)
Stop-12                   78.3µs ± 3%  73.6µs ± 3%   -6.01%  (p=0.000 n=9+10)
SimultaneousAfterFunc-12   138µs ± 1%   111µs ± 1%  -19.57%  (p=0.000 n=10+9)
StartStop-12              28.7µs ± 1%  31.5µs ± 5%   +9.64%  (p=0.000 n=10+7)
Reset-12                  6.78µs ± 1%  4.24µs ± 7%  -37.45%  (p=0.000 n=9+10)
Sleep-12                   183µs ± 1%   125µs ± 1%  -31.67%  (p=0.000 n=10+9)
Ticker-12                 5.40ms ± 2%  0.03ms ± 1%  -99.43%  (p=0.000 n=10+10)
Sub-12                     114ns ± 1%   113ns ± 3%     ~     (p=0.069 n=9+10)
Now-12                    37.2ns ± 1%  36.8ns ± 3%     ~     (p=0.287 n=8+8)
NowUnixNano-12            38.1ns ± 2%  37.4ns ± 3%   -1.87%  (p=0.020 n=10+9)
Format-12                  252ns ± 2%   195ns ± 3%  -22.61%  (p=0.000 n=9+10)
FormatNow-12               234ns ± 1%   177ns ± 2%  -24.34%  (p=0.000 n=10+10)
MarshalJSON-12             320ns ± 2%   250ns ± 0%  -21.94%  (p=0.000 n=8+8)
MarshalText-12             320ns ± 2%   245ns ± 2%  -23.30%  (p=0.000 n=9+10)
Parse-12                   206ns ± 2%   208ns ± 4%     ~     (p=0.084 n=10+10)
ParseDuration-12          89.1ns ± 1%  86.6ns ± 3%   -2.78%  (p=0.000 n=10+10)
Hour-12                   4.43ns ± 2%  4.46ns ± 1%     ~     (p=0.324 n=10+8)
Second-12                 4.47ns ± 1%  4.40ns ± 3%     ~     (p=0.145 n=9+10)
Year-12                   14.6ns ± 1%  14.7ns ± 2%     ~     (p=0.112 n=9+9)
Day-12                    20.1ns ± 3%  20.2ns ± 1%     ~     (p=0.404 n=10+9)

Updates #6239
Updates #27707

Change-Id: I51e25a90f941574f1a9cf83a22e84ac8c678537d
Reviewed-on: https://go-review.googlesource.com/c/go/+/171883
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
Reviewed-by: Emmanuel Odeke <emm.odeke@gmail.com>

The addAdjustedTimers function was a late addition, and it got some of
the state machine wrong, leading to failures like
https://storage.googleapis.com/go-build-log/930576b6/windows-amd64-2016_53d0319e.log

Updates #6239
Updates #27707

Change-Id: I9e94e563b4698ff3035ce609055ca292b9cab3df
Reviewed-on: https://go-review.googlesource.com/c/go/+/204280
Run-TryBot: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Michael Knyszek <mknyszek@google.com>

If multiple goroutines call time.(*Timer).Reset then the timer will go
from timerWaiting to timerDeleted to timerModifying to timerModifiedLater.
The timer can be on a different P, meaning that simultaneously cleantimers
could change it from timerDeleted to timerRemoving to timerRemoved.
If Reset sees timerRemoved, it was doing an atomic.Store of timerWaiting,
meaning that it did not necessarily see the other values set in the timer,
so the timer could appear to be in an inconsistent state. Use atomic.Cas
to avoid that possibility.

Updates #6239
Updates #27707
Fixes #35272

Change-Id: I1d59a13dc4f2ff4af110fc6e032c8c9d59cfc270
Reviewed-on: https://go-review.googlesource.com/c/go/+/204717
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Michael Knyszek <mknyszek@google.com>

When dropping a P, if it has any timers, and if some thread is
sleeping in the netpoller, wake the netpoller to run the P's timers.
This mitigates races between the netpoller deciding how long to sleep
and a new timer being added.

In sysmon, if all P's are idle, check the timers to decide how long to sleep.
This avoids oversleeping if no thread is using the netpoller.
This can happen in particular if some threads use runtime.LockOSThread,
as those threads do not block in the netpoller.

Also, print the number of timers per P for GODEBUG=scheddetail=1.

Before this CL, TestLockedDeadlock2 would fail about 1% of the time.
With this CL, I ran it 150,000 times with no failures.

Updates #6239
Updates #27707
Fixes #35274
Fixes #35288

Change-Id: I7e5193e6c885e567f0b1ee023664aa3e2902fcd1
Reviewed-on: https://go-review.googlesource.com/c/go/+/204800
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Michael Knyszek <mknyszek@google.com>

In the discussion of CL 171828 we decided that it was not necessary to
acquire timersLock around the call to moveTimers, because the world is
stopped. However, that is not correct, as sysmon runs even when the world
is stopped, and it calls timeSleepUntil which looks through the timers.
timeSleepUntil acquires timersLock, but that doesn't help if moveTimers
is running at the same time.

Updates #6239
Updates #27707
Updates #35462

Change-Id: I346c5bde594c4aff9955ae430b37c2b6fc71567f
Reviewed-on: https://go-review.googlesource.com/c/go/+/206938
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Michael Knyszek <mknyszek@google.com>

Dan Scales pointed out a theoretical deadlock in the runtime.

The timer code runs timer functions while holding the timers lock for a P.
The scavenger queues up a timer function that calls wakeScavenger,
which acquires the scavenger lock.

The scavengeSleep function acquires the scavenger lock,
then calls resetTimer which can call addInitializedTimer
which acquires the timers lock for the current P.

So there is a potential deadlock, in that the scavenger lock and
the timers lock for some P may both be acquired in different order.
It's not clear to me whether this deadlock can ever actually occur.

Issue 35532 describes another possible deadlock.

The pollSetDeadline function acquires pd.lock for some poll descriptor,
and in some cases calls resettimer which can in some cases acquire
the timers lock for the current P.

The timer code runs timer functions while holding the timers lock for a P.
The timer function for poll descriptors winds up in netpolldeadlineimpl
which acquires pd.lock.

So again there is a potential deadlock, in that the pd lock for some
poll descriptor and the timers lock for some P may both be acquired in
different order. I think this can happen if we change the deadline
for a network connection exactly as the former deadline expires.

Looking at the code, I don't see any reason why we have to hold
the timers lock while running a timer function.
This CL implements that change.

Updates #6239
Updates #27707
Fixes #35532

Change-Id: I17792f5a0120e01ea07cf1b2de8434d5c10704dd
Reviewed-on: https://go-review.googlesource.com/c/go/+/207348
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Michael Knyszek <mknyszek@google.com>

Updates #6239
Updates #27707

Change-Id: I65e6471829c9de4677d3ac78ef6cd7aa0a1fc4cb
Reviewed-on: https://go-review.googlesource.com/c/go/+/171884
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
Reviewed-by: Emmanuel Odeke <emm.odeke@gmail.com>

We were using the race context of the P that held the timer,
but since we unlock the P's timers while executing a timer
that could lead to a race on the race context itself.

Updates #6239
Updates #27707
Fixes #35906

Change-Id: I5f9d5f52d8e28dffb88c3327301071b16ed1a913
Reviewed-on: https://go-review.googlesource.com/c/go/+/209580
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>
Reviewed-by: Michael Knyszek <mknyszek@google.com>