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go/doc/go1.9.html
Kashav Madan d293c85e39 doc: fix typo in Go 1.9 release notes 
Change-Id: Ia5c8fcff000bf3d369d42407342c470ea92e18da
Reviewed-on: https://go-review.googlesource.com/46006
Reviewed-by: Alberto Donizetti <alb.donizetti@gmail.com>
2017-06-17 08:17:14 +00:00

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<!--{
"Title": "Go 1.9 Release Notes",
"Path": "/doc/go1.9",
"Template": true
}-->
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set fixed-width phrases with non-fixed-width spaces, as in
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<style>
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<h2 id="introduction">DRAFT RELEASE NOTES - Introduction to Go 1.9</h2>
<p><strong>
Go 1.9 is not yet released. These are work-in-progress
release notes. Go 1.9 is expected to be released in August 2017.
</strong></p>
<p>
The latest Go release, version 1.9, arrives six months
after <a href="go1.8">Go 1.8</a> and is the tenth release in
the <a href="https://golang.org/doc/devel/release.html">Go 1.x
series</a>.
There is one <a href="#language">change to the language</a>, adding
support for type aliases.
Most of the changes are in the implementation of the toolchain,
runtime, and libraries.
As always, the release maintains the Go 1
<a href="/doc/go1compat.html">promise of compatibility</a>.
We expect almost all Go programs to continue to compile and run as
before.
</p>
<p>
The release
adds <a href="#monotonic-time">transparent monotonic time support</a>,
<a href="#parallel-compile">parallelizes compilation of functions</a> within a package,
better supports <a href="#test-helper">test helper functions</a>,
includes a new <a href="#math-bits">bit manipulation package</a>,
and has a new <a href="#sync-map">concurrent map type</a>.
</p>
<h2 id="language">Changes to the language</h2>
<p>
There is one change to the language.
Go now supports type aliases to support gradual code repair while
moving a type between packages.
The <a href="https://golang.org/design/18130-type-alias">type alias
design document</a>
and <a href="https://talks.golang.org/2016/refactor.article">an
article on refactoring</a> cover the problem in detail.
In short, a type alias declaration has the form:
</p>
<pre>
type T1 = T2
</pre>
<p>
This declaration introduces an alias name <code>T1</code>—an
alternate spelling—for the type denoted by <code>T2</code>; that is,
both <code>T1</code> and <code>T2</code> denote the same type.
</p>
<h2 id="ports">Ports</h2>
<p>
There are no new supported operating systems or processor
architectures in this release.
</p>
<h3 id="power8">ppc64x requires Power8</h3>
<p> <!-- CL 36725, CL 36832 -->
Both <code>GOARCH=ppc64</code> and <code>GOARCH=ppc64le</code> now
require at least Power8 support. In previous releases,
only <code>GOARCH=ppc64le</code> required Power8 and the big
endian <code>ppc64</code> architecture supported older
hardware.
<p>
<h3 id="known_issues">Known Issues</h3>
<p>
There are some instabilities on FreeBSD that are known but not understood.
These can lead to program crashes in rare cases.
See <a href="https://golang.org/issue/15658">issue 15658</a>.
Any help in solving this FreeBSD-specific issue would be appreciated.
</p>
<h2 id="tools">Tools</h2>
<h3 id="parallel-compile">Parallel Compilation</h3>
<p>
The Go compiler now supports compiling a package's functions in parallel, taking
advantage of multiple cores. This is in addition to the <code>go</code> command's
existing support for parallel compilation of separate packages.
Parallel compilation is on by default, but can be disabled by setting the
environment variable <code>GO19CONCURRENTCOMPILATION</code> to <code>0</code>.
</p>
<h3 id="vendor-dotdotdot">Vendor matching with ./...</h3>
<p><!-- CL 38745 -->
By popular request, <code>./...</code> no longer matches packages
in <code>vendor</code> directories in tools accepting package names,
such as <code>go</code> <code>test</code>. To match vendor
directories, write <code>./vendor/...</code>.
</p>
<h3 id="compiler">Compiler Toolchain</h3>
<p><!-- CL 37441 -->
Complex division is now C99-compatible. This has always been the
case in gccgo and is now fixed in the gc toolchain.
</p>
<p> <!-- CL 36983 -->
The linker will now generate DWARF information for cgo executables on Windows.
</p>
<p> <!-- CL 44210, CL 40095 -->
The compiler now includes lexical scopes in the generated DWARF, allowing
debuggers to hide variables that are not in scope. The <code>.debug_info</code>
section is now DWARF version 4.
</p>
<p> <!-- CL 43855 -->
The values of <code>GOARM</code> and <code>GO386</code> now affect a
compiled package's build ID, as used by the <code>go</code> tool's
dependency caching.
</p>
<h3 id="go-doc">Doc</h3>
<p><!-- CL 36031 -->
Long lists of arguments are now truncated. This improves the readability
of <code>go doc</code> on some generated code.
</p>
<p><!-- CL 38438 -->
Viewing documentation on struct fields is now supported with
<code>go doc struct.field</code>.
</p>
<h3 id="go-env-json">Env</h3>
<p> <!-- CL 38757 -->
The new <code>go</code> <code>env</code> <code>-json</code> flag
enables JSON output, instead of the default OS-specific output
format.
</p>
<h3 id="go-test-list">Test</h3>
<p> <!-- CL 41195 -->
The <a href="/cmd/go/#hdr-Description_of_testing_flags"><code>go</code> <code>test</code></a>
command accepts a new <code>-list</code> flag, which takes a regular
expression as an argument and prints to stdout the name of any
tests, benchmarks, or examples that match it, without running them.
</p>
<h3 id="go-tool-pprof-proxy">Pprof</h3>
<p> <!-- CL 38343 -->
The <code>go</code> <code>tool</code> <code>pprof</code> command now
uses the HTTP proxy information defined in the environment, using
<a href="/pkg/net/http/#ProxyFromEnvironment"><code>http.ProxyFromEnvironment</code></a>.
</p>
<h3 id="tools-TODO">TODO</h3>
<p>TODO: finish documenting misc tool changes</p>
<pre>
CL 42028: https://golang.org/cl/42028: cmd/asm: fix operand order of ARM's MULA instruction
CL 40112: https://golang.org/cl/40112: cmd/go: allow full flag processing in go vet
CL 42990: https://golang.org/cl/42990: cmd/internal/obj/x86: add ADDSUBPS/PD
CL 40331: https://golang.org/cl/40331: cmd/link,runtime/cgo: enable PT_TLS generation on OpenBSD
</pre>
<h2 id="performance">Performance</h2>
<p>
As always, the changes are so general and varied that precise
statements about performance are difficult to make. Most programs
should run a bit faster, due to speedups in the garbage collector,
better generated code, and optimizations in the core library.
</p>
<h3 id="gc">Garbage Collector</h3>
<p> <!-- CL 37520 -->
Library functions that used to trigger stop-the-world garbage
collection now trigger concurrent garbage collection.
Specifically, <a href="/pkg/runtime/#GC"><code>runtime.GC</code></a>,
<a href="/pkg/runtime/debug/#SetGCPercent"><code>debug.SetGCPercent</code></a>,
and
<a href="/pkg/runtime/debug/#FreeOSMemory"><code>debug.FreeOSMemory</code></a>,
now trigger concurrent garbage collection, blocking only the calling
goroutine until the garbage collection is done.
</p>
<p> <!-- CL 34103, CL 39835 -->
The
<a href="/pkg/runtime/debug/#SetGCPercent"><code>debug.SetGCPercent</code></a>
function only triggers a garbage collection if one is immediately
necessary because of the new GOGC value.
This makes it possible to adjust GOGC on-the-fly.
</p>
<p> <!-- CL 38732 -->
Large object allocation performance is significantly improved in
applications using large (&gt;50GB) heaps containing many large
objects.
</p>
<p> <!-- CL 34937 -->
The <a href="/pkg/runtime/#ReadMemStats"><code>runtime.ReadMemStats</code></a>
function now takes less than 100µs even for very large heaps.
</p>
<h2 id="library">Core library</h2>
<h3 id="monotonic-time">Transparent Monotonic Time support</h3>
<p> <!-- CL 36255 -->
The <a href="/pkg/time/"><code>time</code></a> package now transparently
tracks monotonic time in each <a href="/pkg/time/#Time"><code>Time</code></a>
value, making computing durations between two <code>Time</code> values
a safe operation in the presence of wall clock adjustments.
See the <a href="/pkg/time/#hdr-Monotonic_Clocks">package docs</a> and
<a href="https://golang.org/design/12914-monotonic">design document</a>
for details.
</p>
<h3 id="math-bits">New bit manipulation package</h3>
<p> <!-- CL 36315 -->
Go 1.9 includes a new package,
<a href="/pkg/math/bits/"><code>math/bits</code></a>, with optimized
implementations for manipulating bits. On most architectures
functions in this package are additionally recognized by the
compiler and treated as intrinsics for additional performance.
</p>
<h3 id="test-helper">Test Helper Functions</h3>
<p> <!-- CL 38796 -->
The
new <a href="/pkg/testing/#T.Helper"><code>(*T).Helper</code></a>
and <a href="/pkg/testing/#B.Helper"><code>(*B).Helper</code></a>
methods mark the calling function as a test helper function. When
printing file and line information, that function will be skipped.
This permits writing test helper functions while still having useful
line numbers for users.
</p>
<h3 id="sync-map">Concurrent Map</h3>
<p> <!-- CL 36617 -->
The new <a href="/pkg/sync/#Map"><code>Map</code></a> type
in the <a href="/pkg/sync/"><code>sync</code></a> package
is a concurrent map with amortized-constant-time loads, stores, and
deletes. It is safe for multiple goroutines to call a Map's methods
concurrently.
</p>
<h3 id="minor_library_changes">Minor changes to the library</h3>
<p>
As always, there are various minor changes and updates to the library,
made with the Go 1 <a href="/doc/go1compat">promise of compatibility</a>
in mind.
</p>
<dl id="archive/zip"><dt><a href="/pkg/archive/zip/">archive/zip</a></dt>
<dd>
<p><!-- CL 39570 -->
The
ZIP <a href="/pkg/archive/zip/#Writer"><code>Writer</code></a>
now sets the UTF-8 bit in
the <a href="/pkg/archive/zip/#FileHeader.Flags"><code>FileHeader.Flags</code></a>
when appropriate.
</p>
</dl><!-- archive/zip -->
<dl id="crypto/rand"><dt><a href="/pkg/crypto/rand/">crypto/rand</a></dt>
<dd>
<p><!-- CL 43852 -->
On Linux, Go now calls the <code>getrandom</code> system call
without the <code>GRND_NONBLOCK</code> flag; it will now block
until the kernel has sufficient randomness. On kernels predating
the <code>getrandom</code> system call, Go continues to read
from <code>/dev/urandom</code>.
</p>
</dl><!-- crypto/rand -->
<dl id="crypto/x509"><dt><a href="/pkg/crypto/x509/">crypto/x509</a></dt>
<dd>
<p><!-- CL 36093 -->
On Unix systems the environment
variables <code>SSL_CERT_FILE</code>
and <code>SSL_CERT_DIR</code> can now be used to override the
system default locations for the SSL certificate file and SSL
certificate files directory, respectively.
</p>
<p>The FreeBSD path <code>/usr/local/etc/ssl/cert.pem</code> is
now included in the certificate search path.
</p>
<p><!-- CL 36900 -->
The package now supports excluded domains in name constraints.
In addition to enforcing such constraints,
<a href="/pkg/crypto/x509/#CreateCertificate"><code>CreateCertificate</code></a>
will create certificates with excluded name constraints
if the provided template certificate has the new
field
<a href="/pkg/crypto/x509/#Certificate.ExcludedDNSDomains"><code>ExcludedDNSDomains</code></a>
populated.
</p>
</dl><!-- crypto/x509 -->
<dl id="database/sql"><dt><a href="/pkg/database/sql/">database/sql</a></dt>
<dd>
<p><!-- CL 35476 -->
The package will now use a cached <a href="/pkg/database/sql/#Stmt"><code>Stmt</code></a> if
available in <a href="/pkg/database/sql/#Tx.Stmt"><code>Tx.Stmt</code></a>.
This prevents statements from being re-prepared each time
<a href="/pkg/database/sql/#Tx.Stmt"><code>Tx.Stmt</code></a> is called.
</p>
<p><!-- CL 38533 -->
The package now allows drivers to implement their own argument checkers by implementing
<a href="/pkg/database/sql/driver/#NamedValueChecker"><code>driver.NamedValueChecker</code></a>.
This also allows drivers to support <code>OUTPUT</code> and <code>INOUT</code> parameter types.
<a href="/pkg/database/sql/#Out"><code>Out</code></a> should be used to return output parameters
when supported by the driver.
</p>
<p><!-- CL 39031 -->
<a href="/pkg/database/sql/#Rows.Scan"><code>Rows.Scan</code></a> can now scan user-defined string types.
Previously the package supported scanning into numeric types like <code>type Int int64</code>. It now also supports
scanning into string types like <code>type String string</code>.
</p>
<p><!-- CL 40694 -->
The new <a href="/pkg/database/sql/#DB.Conn"><code>DB.Conn</code></a> method returns the new
<a href="/pkg/database/sql/#Conn"><code>Conn</code></a> type representing an
exclusive connection to the database from the connection pool. All queries run on
a <a href="/pkg/database/sql/#Conn"><code>Conn</code></a> will use the same underlying
connection until <a href="/pkg/database/sql/#Conn.Close"><code>Conn.Close</code></a> is called
to return the connection to the connection pool.
</p>
</dl><!-- database/sql -->
<dl id="encoding/asn1"><dt><a href="/pkg/encoding/asn1/">encoding/asn1</a></dt>
<dd>
<p><!-- CL 38660 -->
The new
<a href="/pkg/encoding/asn1/#NullBytes"><code>NullBytes</code></a>
and
<a href="/pkg/encoding/asn1/#NullRawValue"><code>NullRawValue</code></a>
represent the <code>ASN.1 NULL</code> type.
</p>
</dl><!-- encoding/asn1 -->
<dl id="encoding/base32"><dt><a href="/pkg/encoding/base32/">encoding/base32</a></dt>
<dd>
<p><!-- CL 38634 -->
The new <a href="/pkg/encoding/base32/#Encoding.WithPadding">Encoding.WithPadding</a>
method adds support for custom padding characters and disabling padding.
</p>
</dl><!-- encoding/base32 -->
<dl id="encoding/csv"><dt><a href="/pkg/encoding/csv/">encoding/csv</a></dt>
<dd>
<p><!-- CL 41730 -->
The new field
<a href="/pkg/encoding/csv/#Reader.ReuseRecord"><code>Reader.ReuseRecord</code></a>
controls whether calls to
<a href="/pkg/encoding/csv/#Reader.Read"><code>Read</code></a>
may return a slice sharing the backing array of the previous
call's returned slice for improved performance.
</p>
</dl><!-- encoding/csv -->
<dl id="fmt"><dt><a href="/pkg/fmt/">fmt</a></dt>
<dd>
<p><!-- CL 37051 -->
The sharp flag ('<code>#</code>') is now supported when printing
floating point and complex numbers. It will always print a
decimal point
for <code>%e</code>, <code>%E</code>, <code>%f</code>, <code>%F</code>, <code>%g</code>
and <code>%G</code>; it will not remove trailing zeros
for <code>%g</code> and <code>%G</code>.
</p>
</dl><!-- fmt -->
<dl id="hash/fnv"><dt><a href="/pkg/hash/fnv/">hash/fnv</a></dt>
<dd>
<p><!-- CL 38356 -->
The package now includes 128-bit FNV-1 and FNV-1a hash support with
<a href="/pkg/hash/fnv/#New128"><code>New128</code></a> and
<a href="/pkg/hash/fnv/#New128a"><code>New128a</code></a>, respectively.
</p>
</dl><!-- hash/fnv -->
<dl id="html/template"><dt><a href="/pkg/html/template/">html/template</a></dt>
<dd>
<p><!-- CL 37880, CL 40936 -->
The package now reports an error if a predefined escaper (one of
"html", "urlquery" and "js") is found in a pipeline and its
rewriting by the contextual auto-escaper could potentially lead
to security or correctness issues.
</p>
</dl><!-- html/template -->
<dl id="image"><dt><a href="/pkg/image/">image</a></dt>
<dd>
<p><!-- CL 36734 -->
The <a href="/pkg/image/#Rectangle.Intersect"><code>Rectangle.Intersect</code></a>
method now returns a zero <code>Rectangle</code> when called on
adjacent but non-overlapping rectangles, as documented. In
earlier releases it would incorrectly return an empty but
non-zero <code>Rectangle</code>.
</p>
</dl><!-- image -->
<dl id="image/color"><dt><a href="/pkg/image/color/">image/color</a></dt>
<dd>
<p><!-- CL 36732 -->
The YCbCr to RGBA conversion formula has been tweaked to ensure
that rounding adjustments span the complete [0, 0xffff] RGBA
range.
</p>
</dl><!-- image/color -->
<dl id="image/png"><dt><a href="/pkg/image/png/">image/png</a></dt>
<dd>
<p><!-- CL 34150 -->
The new <a href="/pkg/image/png/#Encoder.BufferPool"><code>Encoder.BufferPool</code></a>
field allows specifying an <a href="/pkg/image/png/#EncoderBufferPool"><code>EncoderBufferPool</code></a>,
that will be used by the encoder to get temporary <code>EncoderBuffer</code>
buffers when encoding a PNG image.
The use of a <code>BufferPool</code> reduces the number of
memory allocations performed while encoding multiple images.
</p>
<p><!-- CL 38271 -->
The package now supports the decoding of transparent 8-bit
grayscale ("Gray8") images.
</p>
</dl><!-- image/png -->
<dl id="math/big"><dt><a href="/pkg/math/big/">math/big</a></dt>
<dd>
<p><!-- CL 36487 -->
The new
<a href="/pkg/math/big/#Int.IsInt64"><code>IsInt64</code></a>
and
<a href="/pkg/math/big/#Int.IsUint64"><code>IsUint64</code></a>
methods report whether an <code>Int</code>
may be represented as an <code>int64</code> or <code>uint64</code>
value.
</p>
</dl><!-- math/big -->
<dl id="mime/multipart"><dt><a href="/pkg/mime/multipart/">mime/multipart</a></dt>
<dd>
<p><!-- CL 39223 -->
The new
<a href="/pkg/mime/multipart/#FileHeader.Size"><code>FileHeader.Size</code></a>
field describes the size of a file in a multipart message.
</p>
</dl><!-- mime/multipart -->
<dl id="net"><dt><a href="/pkg/net/">net</a></dt>
<dd>
<p><!-- CL 32572 -->
The new
<a href="/pkg/net/#Resolver.StrictErrors"><code>Resolver.StrictErrors</code></a>
provides control over how Go's built-in DNS resolver handles
temporary errors during queries composed of multiple sub-queries,
such as an A+AAAA address lookup.
</p>
<p><!-- CL 37260 -->
The new
<a href="/pkg/net/#Resolver.Dial"><code>Resolver.Dial</code></a>
allows a <code>Resolver</code> to use a custom dial function.
</p>
<p><!-- CL 40510 -->
<a href="/pkg/net/#JoinHostPort"><code>JoinHostPort</code></a> now only places an address in square brackets if the host contains a colon.
In previous releases it would also wrap addresses in square brackets if they contained a percent ('<code>%</code>') sign.
</p>
<p><!-- CL 37913 -->
The new methods
<a href="/pkg/net/#TCPConn.SyscallConn"><code>TCPConn.SyscallConn</code></a>,
<a href="/pkg/net/#IPConn.SyscallConn"><code>IPConn.SyscallConn</code></a>,
<a href="/pkg/net/#UDPConn.SyscallConn"><code>UDPConn.SyscallConn</code></a>,
and
<a href="/pkg/net/#UnixConn.SyscallConn"><code>UnixConn.SyscallConn</code></a>
provide access to the connections' underlying file descriptors.
</p>
<p><!-- 45088 -->
It is now safe to call <a href="/pkg/net/#Dial"><code>Dial</code></a> with the address obtained from
<code>(*TCPListener).String()</code> after creating the listener with
<code><a href="/pkg/net/#Listen">Listen</a>("tcp", ":0")</code>.
Previously it failed on some machines with half-configured IPv6 stacks.
</p>
</dl><!-- net -->
<dl id="net/http"><dt><a href="/pkg/net/http/">net/http</a></dt>
<dd>
<p>Server changes:</p>
<ul>
<li><!-- CL 38194 -->
<a href="/pkg/net/http/#ServeMux"><code>ServeMux</code></a> now ignores ports in the host
header when matching handlers. The host is matched unmodified for <code>CONNECT</code> requests.
</li>
<li><!-- CL 34727 -->
<a href="/pkg/net/http/#Server.WriteTimeout"><code>Server.WriteTimeout</code></a>
now applies to HTTP/2 connections and is enforced per-stream.
</li>
<li><!-- CL 43231 -->
HTTP/2 now uses the priority write scheduler by default.
Frames are scheduled by following HTTP/2 priorities as described in
<a href="https://tools.ietf.org/html/rfc7540#section-5.3">RFC 7540 Section 5.3</a>.
</li>
</ul>
<p>Client &amp; Transport changes:</p>
<ul>
<li><!-- CL 35488 -->
The <a href="/pkg/net/http/#Transport"><code>Transport</code></a>
now supports making requests via SOCKS5 proxy when the URL returned by
<a href="/net/http/#Transport.Proxy"><code>Transport.Proxy</code></a>
has the scheme <code>socks5</code>.
</li>
</ul>
</dl><!-- net/http -->
<dl id="net/http/fcgi"><dt><a href="/pkg/net/http/fcgi/">net/http/fcgi</a></dt>
<dd>
<p><!-- CL 40012 -->
The new
<a href="/pkg/net/http/fcgi/#ProcessEnv"><code>ProcessEnv</code></a>
function returns FastCGI environment variables associated with an HTTP request
for which there are no appropriate
<a href="/pkg/net/http/#Request"><code>http.Request</code></a>
fields, such as <code>REMOTE_USER</code>.
</p>
</dl><!-- net/http/fcgi -->
<dl id="net/http/httptest"><dt><a href="/pkg/net/http/httptest/">net/http/httptest</a></dt>
<dd>
<p><!-- CL 34639 -->
The new
<a href="/pkg/net/http/httptest/#Server.Client"><code>Server.Client</code></a>
method returns an HTTP client configured for making requests to the test server.
</p>
<p>
The new
<a href="/pkg/net/http/httptest/#Server.Certificate"><code>Server.Certificate</code></a>
method returns the test server's TLS certificate, if any.
</p>
</dl><!-- net/http/httptest -->
<dl id="os"><dt><a href="/pkg/os/">os</a></dt>
<dd>
<p><!-- CL 36800 -->
The <code>os</code> package now uses the internal runtime poller
for file I/O.
This reduces the number of threads required for read/write
operations on pipes, and eliminates races when one goroutine
closes a file while another using it for I/O.
</p>
<dd>
<p><!-- CL 37915 -->
On Windows,
<a href="/pkg/os/#Args"><code>Args</code></a>
is now populated without <code>shell32.dll</code>, improving process start-up time by 1-7 ms.
</p>
</dl><!-- os -->
<dl id="os/exec"><dt><a href="/pkg/os/exec/">os/exec</a></dt>
<dd>
<p><!-- CL 37586 -->
The <code>os/exec</code> package now prevents child processes from being created with
any duplicate environment variables.
If <a href="/pkg/os/exec/#Cmd.Env"><code>Cmd.Env</code></a>
contains duplicate environment keys, only the last
value in the slice for each duplicate key is used.
</p>
</dl><!-- os/exec -->
<dl id="os/user"><dt><a href="/pkg/os/user/">os/user</a></dt>
<dd>
<p><!-- CL 37664 -->
<a href="/pkg/os/user/#Lookup"><code>Lookup</code></a> and
<a href="/pkg/os/user/#LookupId"><code>LookupId</code></a> now
work on Unix systems when <code>CGO_ENABLED=0</code> by reading
the <code>/etc/passwd</code> file.
</p>
<p><!-- CL 33713 -->
<a href="/pkg/os/user/#LookupGroup"><code>LookupGroup</code></a> and
<a href="/pkg/os/user/#LookupGroupId"><code>LookupGroupId</code></a> now
work on Unix systems when <code>CGO_ENABLED=0</code> by reading
the <code>/etc/group</code> file.
</p>
</dl><!-- os/user -->
<dl id="reflect"><dt><a href="/pkg/reflect/">reflect</a></dt>
<dd>
<p><!-- CL 38335 -->
The new
<a href="/pkg/reflect/#MakeMapWithSize"><code>MakeMapWithSize</code></a>
function creates a map with a capacity hint.
</p>
</dl><!-- reflect -->
<dl id="runtime"><dt><a href="/pkg/runtime/">runtime</a></dt>
<dd>
<p><!-- CL 37233, CL 37726 -->
Tracebacks generated by the runtime and recorded in profiles are
now accurate in the presence of inlining.
To retrieve tracebacks programmatically, applications should use
<a href="/pkg/runtime/#CallersFrames"><code>runtime.CallersFrames</code></a>
rather than directly iterating over the results of
<a href="/pkg/runtime/#Callers"><code>runtime.Callers</code></a>.
</p>
<p><!-- CL 38403 -->
On Windows, Go no longer forces the system timer to run at high
resolution when the program is idle.
This should reduce the impact of Go programs on battery life.
</p>
<p><!-- CL 29341 -->
On FreeBSD, <code>GOMAXPROCS</code> and
<a href="/pkg/runtime/#NumCPU"><code>runtime.NumCPU</code></a>
are now based on the process' CPU mask, rather than the total
number of CPUs.
</p>
<p><!-- CL 43641 -->
The runtime has preliminary support for Android O.
</p>
</dl><!-- runtime -->
<dl id="runtime/pprof"><dt><a href="/pkg/runtime/pprof/">runtime/pprof</a></dt>
<dd>
<p><!-- CL 34198 -->
TODO: <a href="https://golang.org/cl/34198">https://golang.org/cl/34198</a>: add definitions of profile label types
</p>
</dl><!-- runtime/pprof -->
<dl id="runtime/debug"><dt><a href="/pkg/runtime/debug/">runtime/debug</a></dt>
<dd>
<p><!-- CL 34013 -->
Calling
<a href="/pkg/runtime/debug/#SetGCPercent"><code>SetGCPercent</code></a>
with a negative value no longer runs an immediate garbage collection.
</p>
</dl><!-- runtime/debug -->
<dl id="runtime/trace"><dt><a href="/pkg/runtime/trace/">runtime/trace</a></dt>
<dd>
<p><!-- CL 36015 -->
The execution trace now displays mark assist events, which
indicate when an application goroutine is forced to assist
garbage collection because it is allocating too quickly.
</p>
<p><!-- CL 40810 -->
"Sweep" events now encompass the entire process of finding free
space for an allocation, rather than recording each individual
span that is swept.
This reduces allocation latency when tracing allocation-heavy
programs.
The sweep event shows how many bytes were swept and how many
were reclaimed.
</p>
</dl><!-- runtime/trace -->
<dl id="sync"><dt><a href="/pkg/sync/">sync</a></dt>
<dd>
<p><!-- CL 34310 -->
<a href="/pkg/sync/#Mutex"><code>Mutex</code></a> is now more fair.
</p>
</dl><!-- sync -->
<dl id="syscall"><dt><a href="/pkg/syscall/">syscall</a></dt>
<dd>
<p><!-- CL 36697 -->
The new field
<a href="/pkg/syscall/#Credential.NoSetGroups"><code>Credential.NoSetGroups</code></a>
controls whether Unix systems make a <code>setgroups</code> system call
to set supplementary groups when starting a new process.
</p>
<p><!-- CL 37439 -->
On 64-bit x86 Linux, process creation latency has been optimized with
use of <code>CLONE_VFORK</code> and <code>CLONE_VM</code>.
</p>
<p><!-- CL 37913 -->
The new
<a href="/pkg/syscall/#Conn"><code>Conn</code></a>
interface describes some types in the
<a href="/pkg/net/"><code>net</code></a>
package that can provide access to their underlying file descriptor
using the new
<a href="/pkg/syscall/#RawConn"><code>RawConn</code></a>
interface.
</p>
</dl><!-- syscall -->
<dl id="testing/quick"><dt><a href="/pkg/testing/quick/">testing/quick</a></dt>
<dd>
<p><!-- CL 39152 -->
The package now chooses values in the full range when
generating <code>int64</code> and <code>uint64</code> random
numbers; in earlier releases generated values were always
limited to the [-2<sup>62</sup>, 2<sup>62</sup>) range.
</p>
</dl><!-- testing/quick -->
<dl id="text/template"><dt><a href="/pkg/text/template/">text/template</a></dt>
<dd>
<p><!-- CL 38420 -->
The handling of empty blocks, which was broken by a Go 1.8
change that made the result dependent on the order of templates,
has been fixed, restoring the old Go 1.7 behavior.
</p>
</dl><!-- text/template -->
<dl id="time"><dt><a href="/pkg/time/">time</a></dt>
<dd>
<p><!-- CL 36615 -->
The new methods
<a href="/pkg/time/#Duration.Round"><code>Duration.Round</code></a>
and
<a href="/pkg/time/#Duration.Truncate"><code>Duration.Truncate</code></a>
handle rounding and truncating durations to multiples of a given duration.
</p>
<p><!-- CL 35710 -->
Retrieving the time and sleeping now work correctly under Wine.
</p>
<p>
If a <code>Time</code> value has a monotonic clock reading, its
string representation (as returned by <code>String</code>) now includes a
final field <code>"m=±value"</code>, where <code>value</code> is the
monotonic clock reading formatted as a decimal number of seconds.
</p>
<p><!-- CL 44832 -->
The included <code>tzdata</code> timezone database has been
updated to version 2017b. As always, it is only used if the
system does not already have the database available.
</p>
</dl><!-- time -->
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