Depending on how the preemption will occur, in some scenarios sendc
would have blocked indefinitely even after cancelling the context.
Fixes#10315
Signed-off-by: Uri Gorelik <uri.gore@gmail.com>
The LoadFunc loads a value and calls a user-provided function.
The utility of this method is to ensure that the map lock is held
while executing user-provided logic.
This allows us to solve TOCTOU bugs that would be nearly imposible
to the solve without this API.
Updates tailscale/corp#14772
Signed-off-by: Joe Tsai <joetsai@digital-static.net>
I was reviewing some code that was performing this by hand, and wanted
to suggest using syncs.Map, however as the code in question was
allocating a non-trivial structure this would be necessary to meet the
target.
Updates #cleanup
Signed-off-by: James Tucker <james@tailscale.com>
I need this for a corp change where I have a set as a queue, and make a
different decisison if the set is empty.
Updates tailscale/corp#10344
Signed-off-by: James Tucker <james@tailscale.com>
The test is re-enabled for Windows with a relaxed time assertion.
On Windows the runtime poller currently does not have sufficient
resolution to meet the normal requirements for this test.
See https://github.com/golang/go/issues/44343 for background.
Updates #7876
Signed-off-by: James Tucker <jftucker@gmail.com>
We accidentally switched to ./tool/go in
4022796484 which resulted in no longer
running Windows builds, as this is attempting to run a bash script.
I was unable to quickly fix the various tests that have regressed, so
instead I've added skips referencing #7876, which we need to back and
fix.
Updates #7262
Updates #7876
Signed-off-by: James Tucker <james@tailscale.com>
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>
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>
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>
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>
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>
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>
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>
