A proposal discussion in mid-2020 on #37196 decided to change
time.Timer and time.Ticker so that their Stop and Reset methods
guarantee that no old value (corresponding to the previous configuration
of the Timer or Ticker) will be received after the method returns.
The trivial way to do this is to make the Timer/Ticker channels
unbuffered, create a goroutine per Timer/Ticker feeding the channel,
and then coordinate with that goroutine during Stop/Reset.
Since Stop/Reset coordinate with the goroutine and the channel
is unbuffered, there is no possibility of a stale value being sent
after Stop/Reset returns.
Of course, we do not want an extra goroutine per Timer/Ticker,
but that's still a good semantic model: behave like the channels
are unbuffered and fed by a coordinating goroutine.
The actual implementation is more effort but behaves like the model.
Specifically, the timer channel has a 1-element buffer like it always has,
but len(t.C) and cap(t.C) are special-cased to return 0 anyway, so user
code cannot see what's in the buffer except with a receive.
Stop/Reset lock out any stale sends and then clear any pending send
from the buffer.
Some programs will change behavior. For example:
package main
import "time"
func main() {
t := time.NewTimer(2 * time.Second)
time.Sleep(3 * time.Second)
if t.Reset(2*time.Second) != false {
panic("expected timer to have fired")
}
<-t.C
<-t.C
}
This program (from #11513) sleeps 3s after setting a 2s timer,
resets the timer, and expects Reset to return false: the Reset is too
late and the send has already occurred. It then expects to receive
two values: the one from before the Reset, and the one from after
the Reset.
With an unbuffered timer channel, it should be clear that no value
can be sent during the time.Sleep, so the time.Reset returns true,
indicating that the Reset stopped the timer from going off.
Then there is only one value to receive from t.C: the one from after the Reset.
In 2015, I used the above example as an argument against this change.
Note that a correct version of the program would be:
func main() {
t := time.NewTimer(2 * time.Second)
time.Sleep(3 * time.Second)
if !t.Reset(2*time.Second) {
<-t.C
}
<-t.C
}
This works with either semantics, by heeding t.Reset's result.
The change should not affect correct programs.
However, one way that the change would be visible is when programs
use len(t.C) (instead of a non-blocking receive) to poll whether the timer
has triggered already. We might legitimately worry about breaking such
programs.
In 2020, discussing #37196, Bryan Mills and I surveyed programs using
len on timer channels. These are exceedingly rare to start with; nearly all
the uses are buggy; and all the buggy programs would be fixed by the new
semantics. The details are at [1].
To further reduce the impact of this change, this CL adds a temporary
GODEBUG setting, which we didn't know about yet in 2015 and 2020.
Specifically, asynctimerchan=1 disables the change and is the default
for main programs in modules that use a Go version before 1.23.
We hope to be able to retire this setting after the minimum 2-year window.
Setting asynctimerchan=1 also disables the garbage collection change
from CL 568341, although users shouldn't need to know that since
it is not a semantically visible change (unless we have bugs!).
As an undocumented bonus that we do not officially support,
asynctimerchan=2 disables the channel buffer change but keeps
the garbage collection change. This may help while we are
shaking out bugs in either of them.
Fixes#37196.
[1] https://github.com/golang/go/issues/37196#issuecomment-641698749
Change-Id: I8925d3fb2b86b2ae87fd2acd055011cbf7bd5916
Reviewed-on: https://go-review.googlesource.com/c/go/+/568341
Reviewed-by: Austin Clements <austin@google.com>
Auto-Submit: Russ Cox <rsc@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
From the beginning of Go, the time package has had a gotcha:
if you use a select on <-time.After(1*time.Minute), even if the select
finishes immediately because some other case is ready, the underlying
timer from time.After keeps running until the minute is over. This
pins the timer in the timer heap, which keeps it from being garbage
collected and in extreme cases also slows down timer operations.
The lack of garbage collection is the more important problem.
The docs for After warn against this scenario and suggest using
NewTimer with a call to Stop after the select instead, purely to work
around this garbage collection problem.
Oddly, the docs for NewTimer and NewTicker do not mention this
problem, but they have the same issue: they cannot be collected until
either they are Stopped or, in the case of Timer, the timer expires.
(Tickers repeat, so they never expire.) People have built up a shared
knowledge that timers and tickers need to defer t.Stop even though the
docs do not mention this (it is somewhat implied by the After docs).
This CL fixes the garbage collection problem, so that a timer that is
unreferenced can be GC'ed immediately, even if it is still running.
The approach is to only insert the timer into the heap when some
channel operation is blocked on it; the last channel operation to stop
using the timer takes it back out of the heap. When a timer's channel
is no longer referenced, there are no channel operations blocked on
it, so it's not in the heap, so it can be GC'ed immediately.
This CL adds an undocumented GODEBUG asynctimerchan=1
that will disable the change. The documentation happens in
the CL 568341.
Fixes#8898.
Fixes#61542.
Change-Id: Ieb303b6de1fb3527d3256135151a9e983f3c27e6
Reviewed-on: https://go-review.googlesource.com/c/go/+/512355
Reviewed-by: Austin Clements <austin@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Russ Cox <rsc@golang.org>
This CL updates os.Readlink so it no longer tries to normalize volumes
to drive letters, which was not always even possible.
This behavior is controlled by the `winreadlinkvolume` setting.
For Go 1.23, it defaults to `winreadlinkvolume=1`.
Previous versions default to `winreadlinkvolume=0`.
Fixes#63703.
Cq-Include-Trybots: luci.golang.try:gotip-windows-amd64-longtest,gotip-windows-arm64
Change-Id: Icd6fabbc8f0b78e23a82eef8db89940e89e9222d
Reviewed-on: https://go-review.googlesource.com/c/go/+/567735
Reviewed-by: Michael Knyszek <mknyszek@google.com>
Reviewed-by: Bryan Mills <bcmills@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
This CL changes the behavior of os.Lstat to stop setting the
os.ModeSymlink type mode bit for mount points on Windows. As a result,
filepath.EvalSymlinks no longer evaluates mount points, which was the
cause of many inconsistencies and bugs.
Additionally, os.Lstat starts setting the os.ModeIrregular type mode bit
for all reparse tags on Windows, except for those that are explicitly
supported by the os package, which, since this CL, doesn't include mount
points. This helps to identify files that need special handling outside
of the os package.
This behavior is controlled by the `winsymlink` GODEBUG setting.
For Go 1.23, it defaults to `winsymlink=1`.
Previous versions default to `winsymlink=0`.
Fixes#39786Fixes#40176Fixes#61893
Updates #63703
Updates #40180
Updates #63429
Cq-Include-Trybots: luci.golang.try:gotip-windows-amd64-longtest,gotip-windows-arm64
Change-Id: I2e7372ab8862f5062667d30db6958d972bce5407
Reviewed-on: https://go-review.googlesource.com/c/go/+/565136
Reviewed-by: Bryan Mills <bcmills@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
Change-Id: I943a7794dab919b7377661a4b9e2e1d9865f2922
GitHub-Last-Rev: 2a66fce273
GitHub-Pull-Request: golang/go#66063
Reviewed-on: https://go-review.googlesource.com/c/go/+/568495
Auto-Submit: Ian Lance Taylor <iant@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
This reverts CL 542699.
Reason for revert: Some applications assume FindProcess does not return
errors.
For #62654.
Fixes#65866.
Change-Id: Ic185a6253c8e508b08150b618c39a9905f6cdd60
Reviewed-on: https://go-review.googlesource.com/c/go/+/566476
Reviewed-by: Bryan Mills <bcmills@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Michael Pratt <mpratt@google.com>
Amend FindProcess to use pidfdFind, and make it return ErrProcessDone
if pidfdFind is used and the process is not found.
Since this is a change in API, introduce GODEBUG osfinderr=0 setting
to disable the feature.
Change-Id: I724c6f622f0c99f21a70b864cf7cf2b8836869ee
Reviewed-on: https://go-review.googlesource.com/c/go/+/542699
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Reviewed-by: Than McIntosh <thanm@google.com>
Use a GODEBUG to choose which certificate policy field to use. If
x509usepolicies=1 is set, use the Policies field, otherwise use the
PolicyIdentifiers field.
Fixes#64248
Change-Id: I3f0b56102e0bac4ebe800497717c61c58ef3f092
Reviewed-on: https://go-review.googlesource.com/c/go/+/546916
Reviewed-by: Damien Neil <dneil@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
For #57071.
Change-Id: Ic1645af57aa589917c67154a5e4ad0b4edd7ba90
Reviewed-on: https://go-review.googlesource.com/c/go/+/547058
Reviewed-by: Michael Knyszek <mknyszek@google.com>
Reviewed-by: Rhys Hiltner <rhys@justin.tv>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Michael Pratt <mpratt@google.com>
Go 1.21.1 and Go 1.22 have ceased working around an issue with Linux
kernel defaults for transparent huge pages that can result in excessive
memory overheads. (https://bugzilla.kernel.org/show_bug.cgi?id=93111)
Many Linux distributions disable huge pages altogether these days, so
this problem isn't quite as far-reaching as it used to be. Also, the
problem only affects Go programs with very particular memory usage
patterns.
That being said, because the runtime used to actively deal with this
problem (but with some unpredictable behavior), it's preventing users
that don't have a lot of control over their execution environment from
upgrading to Go beyond Go 1.20.
This change adds a GODEBUG to smooth over the transition. The GODEBUG
setting disables transparent huge pages for all heap memory on Linux,
which is much more predictable than restoring the old behavior.
Fixes#64332.
Change-Id: I73b1894337f0f0b1a5a17b90da1221e118e0b145
Reviewed-on: https://go-review.googlesource.com/c/go/+/547475
Reviewed-by: Michael Pratt <mpratt@google.com>
Auto-Submit: Michael Knyszek <mknyszek@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Removes the RSA KEX based ciphers from the default list. This can be
reverted using the tlsrsakex GODEBUG.
Fixes#63413
Change-Id: Id221be3eb2f6c24b91039d380313f0c87d339f98
Reviewed-on: https://go-review.googlesource.com/c/go/+/541517
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Damien Neil <dneil@google.com>
Updates the default from 1.0 -> 1.2 for servers, bringing it in line
with clients. Add a GODEBUG setting, tls10server, which lets users
revert this change.
Fixes#62459
Change-Id: I2b82f85b1c2d527df1f9afefae4ab30a8f0ceb41
Reviewed-on: https://go-review.googlesource.com/c/go/+/541516
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Damien Neil <dneil@google.com>
This CL exports the previously unexported Alias type and
corresponding functions and methods per issue #63223.
Whether Alias types are used or not is controlled by
the gotypesalias setting with the GODEBUG environment
variable. Setting gotypesalias to "1" enables the Alias
types:
GODEBUG=gotypesalias=1
By default, gotypesalias is not set.
Adjust test cases that enable/disable the use of Alias
types to use -gotypesalias=1 or -gotypesalias=0 rather
than -alias and -alias=false for consistency and to
avoid confusion.
For #63223.
Change-Id: I51308cad3320981afac97dd8c6f6a416fdb0be55
Reviewed-on: https://go-review.googlesource.com/c/go/+/541737
Run-TryBot: Robert Griesemer <gri@google.com>
Reviewed-by: Robert Findley <rfindley@google.com>
Auto-Submit: Robert Griesemer <gri@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Robert Griesemer <gri@google.com>
Change-Id: I941b6397e2f09a4abb30c0caf91cc2ff2212a445
Reviewed-on: https://go-review.googlesource.com/c/go/+/536675
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Auto-Submit: Roland Shoemaker <roland@golang.org>
Add the GODEBUG setting httpmuxgo121.
When set to "1", ServeMux behaves exactly like it did in Go 1.21.
Implemented by defining a new, unexported type, serveMux121, that
uses the original code.
Updates #61410.
Change-Id: I0a9d0fe2a2286e442d680393e62895ab50683cea
Reviewed-on: https://go-review.googlesource.com/c/go/+/530461
Run-TryBot: Jonathan Amsterdam <jba@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Damien Neil <dneil@google.com>
The link was missing the /pkg/ prefix.
Fixes#62034.
Change-Id: I96c43f06621e30241e140948129e90f0bd5f8d13
GitHub-Last-Rev: c1e7413f76
GitHub-Pull-Request: golang/go#62040
Reviewed-on: https://go-review.googlesource.com/c/go/+/519575
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>
Auto-Submit: Dmitri Shuralyov <dmitshur@golang.org>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Run-TryBot: Dmitri Shuralyov <dmitshur@golang.org>
Reviewed-by: Bryan Mills <bcmills@google.com>
The Content-Length must be a valid numeric value, empty values should not be accepted.
See: https://www.rfc-editor.org/rfc/rfc9110.html#name-content-lengthFixes#61679
Change-Id: Icbcd933087fe5e50199b62ff34c58bf92a09d3d4
GitHub-Last-Rev: 932e46b55b
GitHub-Pull-Request: golang/go#61865
Reviewed-on: https://go-review.googlesource.com/c/go/+/517336
Reviewed-by: Damien Neil <dneil@google.com>
Auto-Submit: Bryan Mills <bcmills@google.com>
Reviewed-by: Bryan Mills <bcmills@google.com>
Run-TryBot: Damien Neil <dneil@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Add a new GODEBUG setting, tlsmaxrsasize, which allows controlling the
maximum RSA key size we will accept during TLS handshakes.
Change-Id: I52f060be132014d219f4cd438f59990011a35c96
Reviewed-on: https://go-review.googlesource.com/c/go/+/517495
Auto-Submit: Roland Shoemaker <roland@golang.org>
Reviewed-by: Russ Cox <rsc@golang.org>
Run-TryBot: Roland Shoemaker <roland@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
When adding MPTCP support to address the proposal #56539, I missed the
GODEBUG setting from Russ Cox's plan:
I am inclined to say that we add MPTCP as an opt-in for a release or
two, and then make it opt-out. There should be a GODEBUG setting (...)
See: https://github.com/golang/go/issues/56539#issuecomment-1309294637
Thanks to andrius4669 for having reported this issue to me.
It makes sense to have this GODEBUG setting not to have to modify
applications to use MPTCP (if available). It can then be useful to
estimate the impact in case we want to switch from opt-in to opt-out
later.
The MPTCP E2E test has been modified to make sure we can enable MPTCP
either via the source code like it was already the case before or with
this environment variable:
GODEBUG=multipathtcp=1
The documentation has been adapted accordingly.
I don't know if it is too late for Go 1.21 but I had to put a version in
the documentation. The modification is small, the risk seems low and
this was supposed to be there from the beginning according to Russ Cox's
specifications. It can also be backported or only be present in the
future v1.22 if it is easier.
Note: I didn't re-open #56539 or open a new one. It is not clear to me
what I should do in this case.
Fixes#56539
Change-Id: I9201f4dc0b99e3643075a34c7032a95528c48fa0
Reviewed-on: https://go-review.googlesource.com/c/go/+/507375
Reviewed-by: Cherry Mui <cherryyz@google.com>
Auto-Submit: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Damien Neil <dneil@google.com>
This change documents the new GODEBUG settings introduced for
html/template and mime/multipart, released with Go 1.19.8 and Go 1.20.3
as part of a security fix.
Updates #59153.
Updates #59234.
Change-Id: I25f4d8245da3301dccccfb44da8ff1a5985392a4
Reviewed-on: https://go-review.googlesource.com/c/go/+/482238
Auto-Submit: Michael Knyszek <mknyszek@google.com>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Michael Knyszek <mknyszek@google.com>
Reviewed-by: Damien Neil <dneil@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
This file is itself template input, so have to hide the template
in the go command example.
Change-Id: Ifc4eaff35ca8dc2fb479f8e28d64c06b2a9c9d3b
Reviewed-on: https://go-review.googlesource.com/c/go/+/480995
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Bryan Mills <bcmills@google.com>
Document the changes to GODEBUG implemented as
part of proposal #56986.
Fixes#56986.
Change-Id: I23153a123e23820c5b22db4767620e037bbdd083
Reviewed-on: https://go-review.googlesource.com/c/go/+/462202
Reviewed-by: Damien Neil <dneil@google.com>
Run-TryBot: Russ Cox <rsc@golang.org>
Reviewed-by: Ian Lance Taylor <iant@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Auto-Submit: Russ Cox <rsc@golang.org>
