Go 1.8 Release Party

Go 1.8 Release Party
Golang Brno meetup
28 February 2017
Rodolfo Carvalho
Red Hat

License and Materials
This presentation is licensed under the Creative Commons Attribution-ShareAlike 4.0
International licence.
The materials for this presentation are available on GitHub:
github.com/davecheney/go-1.8-release-party
You are encouraged to remix, transform, or build upon the material, providing you distribute
your contributions under the same license.
If you have suggestions or corrections to this presentation, please raise an issue on the
GitHub project.

Go 1.8
Go 1.8 is released!
Go 1.8 Announcement
Go 1.8 is the 9th release in the Go 1 series. It follows from the previous version, Go 1.7,
released on the 16th of August, 2016
Go 1.8 Release Notes

What's changed?
So, what's happened in the last six months?
Performance
Compiler changes
Tool changes
Runtime changes
Changes to the standard library

Performance
As always, the changes are so general and varied that precise statements about
performance are di cult to make.
Most programs should run a bit faster, due to speedups in the garbage collector and
optimizations in the standard library.
The new back end, based on static single assignment form (SSA), generates more compact,
more e cient code and provides a better platform for optimizations such as bounds check
elimination.
The new back end reduces the CPU time required by our benchmark programs by 20-
30% on 32-bit ARM systems.
For 64-bit x86 systems, which already used the SSA back end in Go 1.7, the gains are a
more modest 0-10%.
Other architectures will likely see improvements closer to the 32-bit ARM numbers.
Go 1.8 Toolchain Improvements

Garbage Collector
Garbage collection pauses should be signi cantly shorter than they were in Go 1.7, usually
under 100 microseconds and often as low as 10 microseconds.
Garbage Collector Improvements Over Time (ht. @francesc)

Defer
The overhead of deferred function calls has been reduced by nearly half.
name old time/op new time/op delta
Defer-4 75.1ns ± 1% 43.3ns ± 1% -42.31% (p=0.000 n=8+10)
In reality, this speeds up defer by about 2.2X. The two benchmarks
below compare a Lock/defer Unlock pair (DeferLock) with a Lock/Unlock
pair (NoDeferLock). NoDeferLock establishes a baseline cost, so these
two benchmarks together show that this change reduces the overhead of
defer from 61.4ns to 27.9ns.
DeferLock-4 77.4ns ± 1% 43.9ns ± 1% -43.31% (p=0.000 n=10+10)
NoDeferLock-4 16.0ns ± 0% 15.9ns ± 0% -0.39% (p=0.000 n=9+8)
Source: CL 29656
Defer and cgo improvements

Cgo
The overhead of cgo calls is reduced by more than half:
CgoNoop-8 146ns ± 1% 56ns ± 6% -61.57% (p=0.000 n=25+30)
This is the result of merging two defers on the standard cgo calling path.
Less cgo overhead in Go 1.8

Miscellaneous performance improvements
Lots of small updates to the standard library.
There have been optimizations to implementations in the bytes, crypto/aes,
crypto/cipher, crypto/elliptic, crypto/sha256, crypto/sha512, encoding/asn1,
encoding/csv, encoding/hex, encoding/json, hash/crc32, image/color, image/draw,
math, math/big, reflect, regexp, runtime, strconv, strings, syscall, text/template,
and unicode/utf8 packages.
Go 1.8 Standard Library Changes

SSA backend
All backends updated to use the new SSA form. Old "plan9" style compiler backend
deleted.
Big performance improvements for 32-bit ARM.
Easy to add new SSA backends (for values of easy compiler engineers work in). eg, adding
MIPS backend was straight forward, SPARC and RISC-V are rumored to be next.

New parser
Robert Griesemer and Matthew Dempsky replaced the parser.
The new parser removes many of the package level variables which came along for the ride
from the previous YACC based parser.
Removing package level globals is a stepping stone to making the compiler more parallel. In
fact this work has started in the development branch.
This new parser is considerably faster, but in 1.8 is hamstrung by having to convert between
the new style AST and the old version the rest of the compiler expects.
Expect this AST conversion to be removed in Go 1.9.

Compiler speed
About a 12-15% improvement compared to Go 1.7

Struct conversion
When explicitly converting a value from one struct type to another, as of Go 1.8 the tags are
ignored.
func example() {
type T1 struct {
X int `json:"foo"`
}
type T2 struct {
X int `json:"bar"`
}
var v1 T1
var v2 T2
v1 = T1(v2) // now legal
_ = v1
} Run

Ports
The number of platforms Go supports, on balance, continues to grow.
Go now supports 32-bit MIPS on Linux for both big-endian (linux/mips) and little-endian
machines (linux/mipsle) that implement the MIPS32r1 instruction set with FPU or kernel
FPU emulation. Note that many common MIPS-based routers lack an FPU and have
rmware that doesn't enable kernel FPU emulation; Go won't run on such machines.
On DragonFly BSD, Go now requires DragonFly 4.4.4 or later.
On OpenBSD, Go now requires OpenBSD 5.9 or later.
The Plan 9 port's networking support is now much more complete and matches the
behavior of Unix and Windows with respect to deadlines and cancelation.
Go 1.8 now only supports OS X 10.8 or later. This is likely the last Go release to support 10.8.
Compiling Go or running binaries on older OS X versions is untested.

Go 1.8 may be the last to support ARMv5
Supporting ARMv5 has been a problem for several releases.
Currently we have no ARMv5 builders so have no idea if Go 1.8 actually works on real ARMv5
hardware (we test on ARMv7).
Several companies have complained about loosing ARMv5 support, and several have
o ered to run a builder -- but there are still no real ARMv5 builders on the dashboard.
If you or your company care about ARMv5, you have to shoulder some of the burden.
Contact @brad tz and set up a builder.
Proposal: runtime: drop support for linux/armv5E and linux/armv6
Dashboard Builders (wiki)
No ARMv5 builders means ARMv5 support will be dropped in Go 1.9.

go tool yacc
The yacc tool (previously available by running “go tool yacc”) has been removed. As of Go 1.7
it was no longer used by the Go compiler.
It has moved to the “tools” repository and is now available at golang.org/x/tools/cmd/goyacc.

go tool asm
go tool asm now supports a otilla of Intel and PPC vector instructions.
For 64-bit x86 systems, the following instructions have been added: VBROADCASTSD,
BROADCASTSS, MOVDDUP, MOVSHDUP, MOVSLDUP, VMOVDDUP, VMOVSHDUP, and VMOVSLDUP.
For 64-bit PPC systems, the common vector scalar instructions have been added: LXS,
LXSDX, LXSI, LXSIWAX, LXSIWZX, LXV, LXVD2X, LXVDSX, LXVW4X, MFVSR, MFVSRD, MFVSRWZ,
MTVSR, MTVSRD, MTVSRWA, MTVSRWZ, STXS, STXSDX, STXSI, STXSIWX, STXV, STXVD2X, STXVW4X,
XSCV, XSCVDPSP, XSCVDPSPN, XSCVDPSXDS, XSCVDPSXWS, XSCVDPUXDS, XSCVDPUXWS,
XSCVSPDP, XSCVSPDPN, XSCVSXDDP, XSCVSXDSP, XSCVUXDDP, XSCVUXDSP, XSCVX, XSCVXP,
XVCV, XVCVDPSP, XVCVDPSXDS, XVCVDPSXWS, XVCVDPUXDS, XVCVDPUXWS, XVCVSPDP,
XVCVSPSXDS, XVCVSPSXWS, XVCVSPUXDS, XVCVSPUXWS, XVCVSXDDP, XVCVSXDSP, XVCVSXWDP,
XVCVSXWSP, XVCVUXDDP, XVCVUXDSP, XVCVUXWDP, XVCVUXWSP, XVCVX, XVCVXP, XXLAND,
XXLANDC, XXLANDQ, XXLEQV, XXLNAND, XXLNOR, XXLOR, XXLORC, XXLORQ, XXLXOR, XXMRG,
XXMRGHW, XXMRGLW, XXPERM, XXPERMDI, XXSEL, XXSI, XXSLDWI, XXSPLT, and XXSPLTW.

go tool trace
The trace tool has a new -pprof ag for producing pprof-compatible blocking and latency
pro les from an execution trace.
Garbage collection events are now shown more clearly in the execution trace viewer.
Garbage collection activity is shown on its own row and GC helper goroutines are annotated
with their roles.
Rhys Hiltner's execution tracer presentation (dotGo 2016)

go tool vet
Vet is stricter in some ways and looser where it previously caused false positives. Vet now
checks for:
copying an array of locks
duplicate JSON and XML struct eld tags
non-space-separated struct tags
deferred calls to HTTP Response.Body.Close before checking errors
indexed arguments in Printf.
package main
type T struct {
A string `json:"A"`
B string `json:"A"`
C string `json:"C"xml:"C"`
}
go tool vet examples/vet_repeated_json_tags.go Run

go x
go fix now rewrites references to golang.org/x/net/context to the standard library
provided context package.

go bug
The new go bug command starts a bug report on GitHub, pre lled with information about
the current system.
Example:
go bug Run

Default $GOPATH
Lastly, it is no longer necessary to set $GOPATH before using the go command.
When GOPATH is not de ned, the tool will use:
$HOME/go on Unix
%USERPROFILE%go on Windows
If you don't like these defaults, just set $GOPATH to your preferred location.

Mutex contention pro le
Peter Wienberger has added a new pprof pro le, mutex contention.
func BenchmarkMutex(b *testing.B) {
const N = 16
for n := 0; n < b.N; n++ {
var done sync.WaitGroup
done.Add(N)
m := Map{m: make(map[string]int)}
for i := 0; i < N; i++ {
go func(i int) {
defer done.Done()
m.Put("foo", i)
}(i)
}
done.Wait()
}
}
note: Due to an oversight this only works with sync.Mutex, not sync.RWMutex, this
oversight will be addressed early in Go 1.9.
runtime: contended mutex pro ling doesn't work for sync.RWMutex

Mutex contention pro le
% go test examples/mutex_test.go -bench=. -mutexprofile=mutex.out
% go tool pprof mutex.test mutex.out
(pprof) list
Total: 290.81ms
ROUTINE ======================== command-line-arguments.(*Map).Put in /Users/dfc/devel/go-1.8-release-party/e
0 290.81ms (flat, cum) 100% of Total
. . 9:}
. . 10:
. . 11:func (m *Map) Put(key string, val int) {
. . 12: m.Lock()
. . 13: m.m[key] = val
. 290.81ms 14: m.Unlock()
. . 15:}
. . 16:
. . 17:func BenchmarkMutex(b *testing.B) {
. . 18: const N = 16
. . 19: for n := 0; n < b.N; n++ {

Plugins
Go now supports a “plugin” build mode for generating plugins written in Go, and a new
plugin package for loading such plugins at run time.
Plugin support is currently only available on Linux.

Plugin Example
package main
// // No C code needed.
import "C"
import "fmt"
var V int
func init() {
fmt.Println("Plugin loading")
}
func F() {
fmt.Printf("Hello, number %dn", V)
}
Then to build plugin.so
$ go build -buildmode=plugin plugin.go

Plugin Example - Using Plugin
fmt.Printf("main started...n")
p, err := plugin.Open("plugin.so")
if err != nil {
panic(err)
}
v, err := p.Lookup("V")
if err != nil {
panic(err)
}
f, err := p.Lookup("F")
if err != nil {
panic(err)
}
*v.(*int) = 7
f.(func())() // prints "Hello, number 7"
$ go run main.go
main started...
Plugin loading
Hello, number 7

Plugins demo
Demo video: twitter.com/francesc
Source code: github.com/campoy/golang-plugins

os.Executable
os.Executable returns an absolute path to the currently running program.
Executable returns the path name for the executable that started the current process.
There is no guarantee that the path is still pointing to the correct executable.
If a symlink was used to start the process, depending on the operating system, the result
might be the symlink or the path it pointed to. If a stable result is needed,
path/ lepath.EvalSymlinks might help.
os.Executable (godoc.org)
fmt.Printf("os.Args[0]: %qn", os.Args[0])
exec, _ := os.Executable()
fmt.Printf("os.Executable(): %qn", exec) Run

Detection of concurrent map accesses
In Go 1.6, the runtime added lightweight, best-e ort detection of concurrent misuse of
maps. Go 1.8 improves that detector with support for detecting programs that concurrently
write to and iterate over a map.
If the runtime detects this condition, it prints a diagnosis and crashes the program.
func main() {
m := map[int]int{4: 4, 8: 8, 15: 15, 16: 16, 23: 23, 42: 42}
go func() {
for {
for _, v := range m {
_ = v
}
}
}()
for {
for k, _ := range m {
m[k]++
}
}
} Run

Changes to the standard library

sort.Slice
The sort package has a new convenice method sort.Slice
switch strings.ToLower(field) {
case "updated":
sort.Slice(subs, func(i, j int) bool { return subs[i].Updated.After(subs[j].Updated) })
case "trust":
sort.Slice(subs, func(i, j int) bool { return subs[i].Trust > subs[j].Trust })
case "stddev":
sort.Slice(subs, func(i, j int) bool {
var s1, s2 stats.Sample
for _, r := range subs[i].Ratings {
s1.Xs = append(s1.Xs, float64(r.Value))
}
for _, r := range subs[j].Ratings {
s2.Xs = append(s2.Xs, float64(r.Value))
}
return s1.StdDev() < s2.StdDev()
})
case "rating":
fallthrough
default:
sort.Slice(subs, func(i, j int) bool { return subs[i].Rating > subs[j].Rating })
}

HTTP shutdown
A long requested feature, graceful shutdown of a http.Server was added in Go 1.8.
Call Shutdown when a signal is received:
func main() {
srv := &http.Server{Addr: ":8080", Handler: http.DefaultServeMux}
go func() {
fmt.Println("Press enter to shutdown server")
fmt.Scanln()
log.Println("Shutting down server...")
if err := srv.Shutdown(context.Background()); err != nil {
log.Fatalf("could not shutdown: %v", err)
}
}()
http.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
fmt.Fprintln(w, "Happy Go 1.8'th")
})
if err := srv.ListenAndServe(); err != http.ErrServerClosed {
log.Fatalf("listen: %sn", err)
}
}

HTTP/2
http.Response now satis es the http.Pusher interface.
type Pusher interface {
Push(target string, opts *PushOptions) error
}

More context support
Continuing Go 1.7's adoption of context.Context into the standard library, Go 1.8 adds
more context support to existing packages:
The new Server.Shutdown takes a context argument.
There have been signi cant additions to the database/sql package with context
support.
All nine of the new Lookup methods on the new net.Resolver now take a context.

Minor changes
Minor library changes

What's coming up in Go 1.9
Before we close, let's quickly touch on some of the things coming up in Go 1.9
note: All of these are speculation, nothing is set in stone until code hits the repo.

Aliases
After being rolled back before the Go 1.8 freeze, aliases are being re-proposed for Go 1.9 in a
more limited fashion.
golang.org/design/18130-type-alias
package main
type A struct { a int }
type B struct { a int }
type C B
type D = B
func main() {
var ( a A; b B; c C; d D )
a = b // nope
b = c // also nope
d = b // new in Go 1.9!
} Run

Faster / cheaper runtime.MemStats
The cost of calling runtime.MemStats is propotional to the size of the heap; Austin recently
timed it at ~1.7ms per Gb.
There is a CL ready to land that reduces it to 20 us per proc (thread servicing a goroutine)
which is a much smaller upper bound.
golang.org/issue/13613

Improvements to the inliner
Inlining has historically been limited to leaf functions because of the concern of agressive
inlining on the call graph.
In support of this Robert Griesemer and Matthew Dempsky have been improving the line
number tracking in Go 1.9 to make it exible enough to lift the restriction on non-leaf
functions.
An unnamed intern has been hired to work on the inliner for 1.9.
Josh Bleecher-Snyder has also suggest that the cost model for inlining should be revised to
make sure inlining is paying for itself.
Issue 17566

A user level poller
Go has used epoll/kqueue/poll/select for network sockets for years.
Reads/Writes to other le descriptors have traditionally consumed an OS thread during
operation
Recently Ian Lance Taylor landed a refactor that broken our the runtime polling subsystem
and extended to work for the rest of the os package.
net: refactor poller into new internal/poll package
os: use poller for le I/O
There is no sign of a programmer accessible poller, yet.

O cial dependency management tool
Finally!
Peter Bourgon, Edward Muller, Sam Boyer, Jess Frazelle, and Steve Francia have been
working on an o cial dependency management tool, dep.
If you're used to Glide or govendor, you won't be too surprised.
Mailing List Announcement
It's described as pre alpha at the moment, but you should check it out, and let them know
what you think.
github.com/golang/dep

Conclusion
Upgrade to Go 1.8, now!
It's literally the best version of Go, ever.

Thank you
Rodolfo Carvalho
Red Hat
rhcarvalho@gmail.com
http://rodolfocarvalho.net
https://dojo-brno.github.io

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