Commit Graph

22 Commits (ba4e58f429029d1b8d51967aa71ccf3bf36de278)

Author SHA1 Message Date
Joe Tsai dad78f31f3
syncs: add WaitGroup wrapper (#7481)
The addition of WaitGroup.Go in the standard library has been
repeatedly proposed and rejected.
See golang/go#18022, golang/go#23538, and golang/go#39863

In summary, the argument for WaitGroup.Go is that it avoids bugs like:

	go func() {
		wg.Add(1)
		defer wg.Done()
		...
	}()

where the increment happens after execution (not before)
and also (to a lesser degree) because:

	wg.Go(func() {
		...
	})

is shorter and more readble.

The argument against WaitGroup.Go is that the provided function
takes no arguments and so inputs and outputs must closed over
by the provided function. The most common race bug for goroutines
is that the caller forgot to capture the loop iteration variable,
so this pattern may make it easier to be accidentally racy.
However, that is changing with golang/go#57969.

In my experience the probability of race bugs due to the former
still outwighs the latter, but I have no concrete evidence to prove it.

The existence of errgroup.Group.Go and frequent utility of the method
at least proves that this is a workable pattern and
the possibility of accidental races do not appear to
manifest as frequently as feared.

A reason *not* to use errgroup.Group everywhere is that there are many
situations where it doesn't make sense for the goroutine to return an error
since the error is handled in a different mechanism
(e.g., logged and ignored, formatted and printed to the frontend, etc.).
While you can use errgroup.Group by always returning nil,
the fact that you *can* return nil makes it easy to accidentally return
an error when nothing is checking the return of group.Wait.
This is not a hypothetical problem, but something that has bitten us
in usages that was only using errgroup.Group without intending to use
the error reporting part of it.

Thus, add a (yet another) variant of WaitGroup here that
is identical to sync.WaitGroup, but with an extra method.

Signed-off-by: Joe Tsai <joetsai@digital-static.net>
2 years ago
Denton Gentry 9ab992e7a1 syncs: re-enable TestWatchMultipleValues
We've updated to a different set of CI machines since this test
was disabled.

Fixes https://github.com/tailscale/tailscale/issues/1513

Signed-off-by: Denton Gentry <dgentry@tailscale.com>
2 years ago
Will Norris 71029cea2d all: update copyright and license headers
This updates all source files to use a new standard header for copyright
and license declaration.  Notably, copyright no longer includes a date,
and we now use the standard SPDX-License-Identifier header.

This commit was done almost entirely mechanically with perl, and then
some minimal manual fixes.

Updates #6865

Signed-off-by: Will Norris <will@tailscale.com>
2 years ago
Joe Tsai 9a05cdd2b5
syncs: add Map (#6260)
Map is a concurrent safe map that is a trivial wrapper
over a Go map and a sync.RWMutex.

It is optimized for use-cases where the entries change often,
which is the opposite use-case of what sync.Map is optimized for.

The API is patterned off of sync.Map, but made generic.

Signed-off-by: Joe Tsai <joetsai@digital-static.net>
2 years ago
Brad Fitzpatrick da8def8e13 all: remove old +build tags
The //go:build syntax was introduced in Go 1.17:

https://go.dev/doc/go1.17#build-lines

gofmt has kept the +build and go:build lines in sync since
then, but enough time has passed. Time to remove them.

Done with:

    perl -i -npe 's,^// \+build.*\n,,' $(git grep -l -F '+build')

Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
2 years ago
Maisem Ali b75f81ec00 syncs: add generic AtomicValue
Signed-off-by: Maisem Ali <maisem@tailscale.com>
2 years ago
Brad Fitzpatrick 4950fe60bd syncs, all: move to using Go's new atomic types instead of ours
Fixes #5185

Change-Id: I850dd532559af78c3895e2924f8237ccc328449d
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
2 years ago
Josh Bleecher Snyder 997b19545b syncs: use TryLock and TryRLock instead of unsafe
The docs say:

Note that while correct uses of TryLock do exist, they are rare,
and use of TryLock is often a sign of a deeper problem in a particular use of mutexes.

Rare code! Or bad code! Who can tell!

Signed-off-by: Josh Bleecher Snyder <josh@tailscale.com>
3 years ago
Josh Bleecher Snyder cf8fcc1254 syncs: mark as safe for Go 1.18
Signed-off-by: Josh Bleecher Snyder <josh@tailscale.com>
3 years ago
Josh Bleecher Snyder d2aa144dcc syncs: bump known good version to include Go 1.17
Signed-off-by: Josh Bleecher Snyder <josh@tailscale.com>
3 years ago
Josh Bleecher Snyder a5da4ed981 all: gofmt with Go 1.17
This adds "//go:build" lines and tidies up existing "// +build" lines.

Signed-off-by: Josh Bleecher Snyder <josh@tailscale.com>
3 years ago
Brad Fitzpatrick e4fecfe31d wgengine/{monitor,router}: restore Linux ip rules when systemd deletes them
Thanks.

Fixes #1591

Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
3 years ago
David Crawshaw 676e32ad72 syncs: add AtomicUint32
Signed-off-by: David Crawshaw <crawshaw@tailscale.com>
3 years ago
David Crawshaw 297b3d6fa4 staticcheck.conf: turn off noisy lint errors
Signed-off-by: David Crawshaw <crawshaw@tailscale.com>
3 years ago
Josh Bleecher Snyder d3ba860ffd syncs: stop running TestWatchMultipleValues on CI
It's flaky, and not just on Windows.

Signed-off-by: Josh Bleecher Snyder <josharian@gmail.com>
4 years ago
Josh Bleecher Snyder 0807e3e2f7 syncs: disable TestWatchMultipleValues on Windows CI builds
The Windows CI machine experiences significant random execution delays.
For example, in this code from watchdog.go:

done := make(chan bool)
go func() {
	start := time.Now()
	mu.Lock()

There was a 500ms delay from initializing done to locking mu.

This test checks that we receive a sufficient number of events quickly enough.
In the face of random 500ms delays, unsurprisingly, the test fails.

There's not much principled we can do about it.
We could build a system of retries or attempt to detect these random delays,
but that game isn't worth the candle.

Skip the test.

Signed-off-by: Josh Bleecher Snyder <josh@tailscale.com>
4 years ago
Brad Fitzpatrick 77ec80538a syncs: add Semaphore
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
4 years ago
Dmytro Tananayskiy c431382720 Fix receiver in order to be consistent: syncs.WaitGroupChan
Signed-off-by: Dmytro Tananayskiy <dmitriyminer@gmail.com>
4 years ago
Josh Bleecher Snyder 9ab2b32569 syncs: add Watch, for monitoring mutex contention
Signed-off-by: Josh Bleecher Snyder <josh@tailscale.com>
4 years ago
Josh Bleecher Snyder bf24d54143 syncs: add AssertLocked
This allows us to check lock invariants.

It was proposed upstream and rejected in:
https://github.com/golang/go/issues/1366

Signed-off-by: Josh Bleecher Snyder <josh@tailscale.com>
4 years ago
Brad Fitzpatrick d3134ad0c8 syncs: add AtomicBool 4 years ago
Brad Fitzpatrick b4d02a251a syncs: add new package for extra sync types 5 years ago