07 Go 1.7 Release Notes
Go 1.7 Release Notes
Introduction to Go 1.7
The latest Go release, version 1.7, arrives six months after 1.6. Most of its changes are in the implementation of the toolchain, runtime, and libraries. There is one minor change to the language specification. As always, the release maintains the Go 1 promise of compatibility. We expect almost all Go programs to continue to compile and run as before.
The release adds a port to IBM LinuxOne; updates the x86-64 compiler back end to generate more efficient code; includes the context package, promoted from the x/net subrepository and now used in the standard library; and adds support in the testing package for creating hierarchies of tests and benchmarks. The release also finalizes the vendoring support started in Go 1.5, making it a standard feature.
Changes to the language
There is one tiny language change in this release. The section on terminating statements clarifies that to determine whether a statement list ends in a terminating statement, the “final non-empty statement” is considered the end, matching the existing behavior of the gc and gccgo compiler toolchains. In earlier releases the definition referred only to the “final statement,” leaving the effect of trailing empty statements at the least unclear. The go/types
package has been updated to match the gc and gccgo compiler toolchains in this respect. This change has no effect on the correctness of existing programs.
Ports
Go 1.7 adds support for macOS 10.12 Sierra. Binaries built with versions of Go before 1.7 will not work correctly on Sierra.
Go 1.7 adds an experimental port to Linux on z Systems (linux/s390x
) and the beginning of a port to Plan 9 on ARM (plan9/arm
).
The experimental ports to Linux on 64-bit MIPS (linux/mips64
and linux/mips64le
) added in Go 1.6 now have full support for cgo and external linking.
The experimental port to Linux on little-endian 64-bit PowerPC (linux/ppc64le
) now requires the POWER8 architecture or later. Big-endian 64-bit PowerPC (linux/ppc64
) only requires the POWER5 architecture.
The OpenBSD port now requires OpenBSD 5.6 or later, for access to the getentropy(2) system call.
Known Issues
There are some instabilities on FreeBSD that are known but not understood. These can lead to program crashes in rare cases. See issue 16136, issue 15658, and issue 16396. Any help in solving these FreeBSD-specific issues would be appreciated.
Tools
Assembler
For 64-bit ARM systems, the vector register names have been corrected to V0
through V31
; previous releases incorrectly referred to them as V32
through V63
.
For 64-bit x86 systems, the following instructions have been added: PCMPESTRI
, RORXL
, RORXQ
, VINSERTI128
,VPADDD
, VPADDQ
, VPALIGNR
, VPBLENDD
, VPERM2F128
, VPERM2I128
, VPOR
, VPSHUFB
, VPSHUFD
, VPSLLD
, VPSLLDQ
,VPSLLQ
, VPSRLD
, VPSRLDQ
, and VPSRLQ
.
Compiler Toolchain
This release includes a new code generation back end for 64-bit x86 systems, following a proposal from 2015that has been under development since then. The new back end, based on SSA, generates more compact, more efficient 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 5-35%.
For this release, the new back end can be disabled by passing -ssa=0
to the compiler. If you find that your program compiles or runs successfully only with the new back end disabled, please file a bug report.
The format of exported metadata written by the compiler in package archives has changed: the old textual format has been replaced by a more compact binary format. This results in somewhat smaller package archives and fixes a few long-standing corner case bugs.
For this release, the new export format can be disabled by passing -newexport=0
to the compiler. If you find that your program compiles or runs successfully only with the new export format disabled, please file a bug report.
The linker's -X
option no longer supports the unusual two-argument form -X
name
value
, as announced in the Go 1.6 release and in warnings printed by the linker. Use -X
name=value
instead.
The compiler and linker have been optimized and run significantly faster in this release than in Go 1.6, although they are still slower than we would like and will continue to be optimized in future releases.
Due to changes across the compiler toolchain and standard library, binaries built with this release should typically be smaller than binaries built with Go 1.6, sometimes by as much as 20-30%.
On x86-64 systems, Go programs now maintain stack frame pointers as expected by profiling tools like Linux's perf and Intel's VTune, making it easier to analyze and optimize Go programs using these tools. The frame pointer maintenance has a small run-time overhead that varies but averages around 2%. We hope to reduce this cost in future releases. To build a toolchain that does not use frame pointers, set GOEXPERIMENT=noframepointer
when running make.bash
, make.bat
, or make.rc
.
Cgo
Packages using cgo may now include Fortran source files (in addition to C, C++, Objective C, and SWIG), although the Go bindings must still use C language APIs.
Go bindings may now use a new helper function C.CBytes
. In contrast to C.CString
, which takes a Go string
and returns a *C.byte
(a C char*
), C.CBytes
takes a Go []byte
and returns an unsafe.Pointer
(a C void*
).
Packages and binaries built using cgo
have in past releases produced different output on each build, due to the embedding of temporary directory names. When using this release with new enough versions of GCC or Clang (those that support the -fdebug-prefix-map
option), those builds should finally be deterministic.
Gccgo
Due to the alignment of Go's semiannual release schedule with GCC's annual release schedule, GCC release 6 contains the Go 1.6.1 version of gccgo. The next release, GCC 7, will likely have the Go 1.8 version of gccgo.
Go command
The go
command's basic operation is unchanged, but there are a number of changes worth noting.
This release removes support for the GO15VENDOREXPERIMENT
environment variable, as announced in the Go 1.6 release. Vendoring support is now a standard feature of the go
command and toolchain.
The Package
data structure made available to “go
list
” now includes a StaleReason
field explaining why a particular package is or is not considered stale (in need of rebuilding). This field is available to the -f
or -json
options and is useful for understanding why a target is being rebuilt.
The “go
get
” command now supports import paths referring to git.openstack.org
.
This release adds experimental, minimal support for building programs using binary-only packages, packages distributed in binary form without the corresponding source code. This feature is needed in some commercial settings but is not intended to be fully integrated into the rest of the toolchain. For example, tools that assume access to complete source code will not work with such packages, and there are no plans to support such packages in the “go
get
” command.
Go doc
The “go
doc
” command now groups constructors with the type they construct, following godoc
.
Go vet
The “go
vet
” command has more accurate analysis in its -copylock
and -printf
checks, and a new -tests
check that checks the name and signature of likely test functions. To avoid confusion with the new -tests
check, the old, unadvertised -test
option has been removed; it was equivalent to -all
-shadow
.
The vet
command also has a new check, -lostcancel
, which detects failure to call the cancelation function returned by the WithCancel
, WithTimeout
, and WithDeadline
functions in Go 1.7's new context
package (see below). Failure to call the function prevents the new Context
from being reclaimed until its parent is cancelled. (The background context is never cancelled.)
Go tool dist
The new subcommand “go
tool
dist
list
” prints all supported operating system/architecture pairs.
Go tool trace
The “go
tool
trace
” command, introduced in Go 1.5, has been refined in various ways.
First, collecting traces is significantly more efficient than in past releases. In this release, the typical execution-time overhead of collecting a trace is about 25%; in past releases it was at least 400%. Second, trace files now include file and line number information, making them more self-contained and making the original executable optional when running the trace tool. Third, the trace tool now breaks up large traces to avoid limits in the browser-based viewer.
Although the trace file format has changed in this release, the Go 1.7 tools can still read traces from earlier releases.
Performance
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 and optimizations in the core library. On x86-64 systems, many programs will run significantly faster, due to improvements in generated code brought by the new compiler back end. As noted above, in our own benchmarks, the code generation changes alone typically reduce program CPU time by 5-35%.
There have been significant optimizations bringing more than 10% improvements to implementations in thecrypto/sha1
, crypto/sha256
, encoding/binary
, fmt
, hash/adler32
, hash/crc32
, hash/crc64
, image/color
,math/big
, strconv
, strings
, unicode
, and unicode/utf16
packages.
Garbage collection pauses should be significantly shorter than they were in Go 1.6 for programs with large numbers of idle goroutines, substantial stack size fluctuation, or large package-level variables.
Core library
Context
Go 1.7 moves the golang.org/x/net/context
package into the standard library as context
. This allows the use of contexts for cancelation, timeouts, and passing request-scoped data in other standard library packages, including net, net/http, and os/exec, as noted below.
For more information about contexts, see the package documentation and the Go blog post “Go Concurrent Patterns: Context.”
HTTP Tracing
Go 1.7 introduces net/http/httptrace
, a package that provides mechanisms for tracing events within HTTP requests.
Testing
The testing
package now supports the definition of tests with subtests and benchmarks with sub-benchmarks. This support makes it easy to write table-driven benchmarks and to create hierarchical tests. It also provides a way to share common setup and tear-down code. See the package documentation for details.
Runtime
All panics started by the runtime now use panic values that implement both the builtin error
, andruntime.Error
, as required by the language specification.
During panics, if a signal's name is known, it will be printed in the stack trace. Otherwise, the signal's number will be used, as it was before Go1.7.
The new function KeepAlive
provides an explicit mechanism for declaring that an allocated object must be considered reachable at a particular point in a program, typically to delay the execution of an associated finalizer.
The new function CallersFrames
translates a PC slice obtained from Callers
into a sequence of frames corresponding to the call stack. This new API should be preferred instead of direct use of FuncForPC
, because the frame sequence can more accurately describe call stacks with inlined function calls.
The new function SetCgoTraceback
facilitates tighter integration between Go and C code executing in the same process called using cgo.
On 32-bit systems, the runtime can now use memory allocated by the operating system anywhere in the address space, eliminating the “memory allocated by OS not in usable range” failure common in some environments.
The runtime can now return unused memory to the operating system on all architectures. In Go 1.6 and earlier, the runtime could not release memory on ARM64, 64-bit PowerPC, or MIPS.
On Windows, Go programs in Go 1.5 and earlier forced the global Windows timer resolution to 1ms at startup by calling timeBeginPeriod(1)
. Changing the global timer resolution caused problems on some systems, and testing suggested that the call was not needed for good scheduler performance, so Go 1.6 removed the call. Go 1.7 brings the call back: under some workloads the call is still needed for good scheduler performance.
Minor changes to the library
As always, there are various minor changes and updates to the library, made with the Go 1 promise of compatibility in mind.
- bufio
-
In previous releases of Go, if
Reader
'sPeek
method were asked for more bytes than fit in the underlying buffer, it would return an empty slice and the errorErrBufferFull
. Now it returns the entire underlying buffer, still accompanied by the errorErrBufferFull
.
- bytes
-
The new functions
ContainsAny
andContainsRune
have been added for symmetry with thestrings
package.In previous releases of Go, if
Reader
'sRead
method were asked for zero bytes with no data remaining, it would return a count of 0 and no error. Now it returns a count of 0 and the errorio.EOF
.The
Reader
type has a new methodReset
to allow reuse of aReader
.
- compress/flate
-
There are many performance optimizations throughout the package. Decompression speed is improved by about 10%, while compression for
DefaultCompression
is twice as fast.In addition to those general improvements, the
BestSpeed
compressor has been replaced entirely and uses an algorithm similar to Snappy, resulting in about a 2.5X speed increase, although the output can be 5-10% larger than with the previous algorithm.There is also a new compression level
HuffmanOnly
that applies Huffman but not Lempel-Ziv encoding. Forgoing Lempel-Ziv encoding means thatHuffmanOnly
runs about 3X faster than the newBestSpeed
but at the cost of producing compressed outputs that are 20-40% larger than those generated by the newBestSpeed
.It is important to note that both
BestSpeed
andHuffmanOnly
produce a compressed output that is RFC 1951 compliant. In other words, any valid DEFLATE decompressor will continue to be able to decompress these outputs.Lastly, there is a minor change to the decompressor's implementation of
io.Reader
. In previous versions, the decompressor deferred reportingio.EOF
until exactly no more bytes could be read. Now, it reportsio.EOF
more eagerly when reading the last set of bytes.
- crypto/tls
-
The TLS implementation sends the first few data packets on each connection using small record sizes, gradually increasing to the TLS maximum record size. This heuristic reduces the amount of data that must be received before the first packet can be decrypted, improving communication latency over low-bandwidth networks. Setting
Config
'sDynamicRecordSizingDisabled
field to true forces the behavior of Go 1.6 and earlier, where packets are as large as possible from the start of the connection.The TLS client now has optional, limited support for server-initiated renegotiation, enabled by setting the
Config
'sRenegotiation
field. This is needed for connecting to many Microsoft Azure servers.The errors returned by the package now consistently begin with a
tls:
prefix. In past releases, some errors used acrypto/tls:
prefix, some used atls:
prefix, and some had no prefix at all.When generating self-signed certificates, the package no longer sets the “Authority Key Identifier” field by default.
- crypto/x509
-
The new function
SystemCertPool
provides access to the entire system certificate pool if available. There is also a new associated error typeSystemRootsError
.
- debug/dwarf
-
The
Reader
type's newSeekPC
method and theData
type's newRanges
method help to find the compilation unit to pass to aLineReader
and to identify the specific function for a given program counter.
- encoding/asn1
-
The ASN.1 decoder now rejects non-minimal integer encodings. This may cause the package to reject some invalid but formerly accepted ASN.1 data.
- encoding/json
-
The
Encoder
's newSetIndent
method sets the indentation parameters for JSON encoding, like in the top-levelIndent
function.The
Encoder
's newSetEscapeHTML
method controls whether the&
,<
, and>
characters in quoted strings should be escaped as\u0026
,\u003c
, and\u003e
, respectively. As in previous releases, the encoder defaults to applying this escaping, to avoid certain problems that can arise when embedding JSON in HTML.In earlier versions of Go, this package only supported encoding and decoding maps using keys with string types. Go 1.7 adds support for maps using keys with integer types: the encoding uses a quoted decimal representation as the JSON key. Go 1.7 also adds support for encoding maps using non-string keys that implement the
MarshalText
(seeencoding.TextMarshaler
) method, as well as support for decoding maps using non-string keys that implement theUnmarshalText
(seeencoding.TextUnmarshaler
) method. These methods are ignored for keys with string types in order to preserve the encoding and decoding used in earlier versions of Go.When encoding a slice of typed bytes,
Marshal
now generates an array of elements encoded using that byte type'sMarshalJSON
orMarshalText
method if present, only falling back to the default base64-encoded string data if neither method is available. Earlier versions of Go accept both the original base64-encoded string encoding and the array encoding (assuming the byte type also implementsUnmarshalJSON
orUnmarshalText
as appropriate), so this change should be semantically backwards compatible with earlier versions of Go, even though it does change the chosen encoding.
- go/build
-
To implement the go command's new support for binary-only packages and for Fortran code in cgo-based packages, the
Package
type adds new fieldsBinaryOnly
,CgoFFLAGS
, andFFiles
.
- go/doc
-
To support the corresponding change in
go
test
described above,Example
struct adds a Unordered field indicating whether the example may generate its output lines in any order.
- io
-
The package adds new constants
SeekStart
,SeekCurrent
, andSeekEnd
, for use withSeeker
implementations. These constants are preferred overos.SEEK_SET
,os.SEEK_CUR
, andos.SEEK_END
, but the latter will be preserved for compatibility.
- math/big
-
The
Float
type addsGobEncode
andGobDecode
methods, so that values of typeFloat
can now be encoded and decoded using theencoding/gob
package.
- math/rand
-
The
Read
function andRand
'sRead
method now produce a pseudo-random stream of bytes that is consistent and not dependent on the size of the input buffer.The documentation clarifies that Rand's
Seed
andRead
methods are not safe to call concurrently, though the global functionsSeed
andRead
are (and have always been) safe.
- mime/multipart
-
The
Writer
implementation now emits each multipart section's header sorted by key. Previously, iteration over a map caused the section header to use a non-deterministic order.
- net
-
As part of the introduction of context, the
Dialer
type has a new methodDialContext
, likeDial
but adding thecontext.Context
for the dial operation. The context is intended to obsolete theDialer
'sCancel
andDeadline
fields, but the implementation continues to respect them, for backwards compatibility.The
IP
type'sString
method has changed its result for invalidIP
addresses. In past releases, if anIP
byte slice had length other than 0, 4, or 16,String
returned"?"
. Go 1.7 adds the hexadecimal encoding of the bytes, as in"?12ab"
.The pure Go name resolution implementation now respects
nsswitch.conf
's stated preference for the priority of DNS lookups compared to local file (that is,/etc/hosts
) lookups.
- net/http
-
ResponseWriter
's documentation now makes clear that beginning to write the response may prevent future reads on the request body. For maximal compatibility, implementations are encouraged to read the request body completely before writing any part of the response.As part of the introduction of context, the
Request
has a new methodsContext
, to retrieve the associated context, andWithContext
, to construct a copy ofRequest
with a modified context.In the
Server
implementation,Serve
records in the request context both the underlying*Server
using the keyServerContextKey
and the local address on which the request was received (aAddr
) using the keyLocalAddrContextKey
. For example, the address on which a request received isreq.Context().Value(http.LocalAddrContextKey).(net.Addr)
.The server's
Serve
method now only enables HTTP/2 support if theServer.TLSConfig
field isnil
or includes"h2"
in itsTLSConfig.NextProtos
.The server implementation now pads response codes less than 100 to three digits as required by the protocol, so that
w.WriteHeader(5)
uses the HTTP response status005
, not just5
.The server implementation now correctly sends only one "Transfer-Encoding" header when "chunked" is set explicitly, following RFC 7230.
The server implementation is now stricter about rejecting requests with invalid HTTP versions. Invalid requests claiming to be HTTP/0.x are now rejected (HTTP/0.9 was never fully supported), and plaintext HTTP/2 requests other than the "PRI * HTTP/2.0" upgrade request are now rejected as well. The server continues to handle encrypted HTTP/2 requests.
In the server, a 200 status code is sent back by the timeout handler on an empty response body, instead of sending back 0 as the status code.
In the client, the
Transport
implementation passes the request context to any dial operation connecting to the remote server. If a custom dialer is needed, the newTransport
fieldDialContext
is preferred over the existingDial
field, to allow the transport to supply a context.The
Transport
also adds fieldsIdleConnTimeout
,MaxIdleConns
, andMaxResponseHeaderBytes
to help control client resources consumed by idle or chatty servers.A
Client
's configuredCheckRedirect
function can now returnErrUseLastResponse
to indicate that the most recent redirect response should be returned as the result of the HTTP request. That response is now available to theCheckRedirect
function asreq.Response
.Since Go 1, the default behavior of the HTTP client is to request server-side compression using the
Accept-Encoding
request header and then to decompress the response body transparently, and this behavior is adjustable using theTransport
'sDisableCompression
field. In Go 1.7, to aid the implementation of HTTP proxies, theResponse
's newUncompressed
field reports whether this transparent decompression took place.DetectContentType
adds support for a few new audio and video content types.
- net/http/cgi
-
The
Handler
adds a new fieldStderr
that allows redirection of the child process's standard error away from the host process's standard error.
- net/http/httptest
-
The new function
NewRequest
prepares a newhttp.Request
suitable for passing to anhttp.Handler
during a test.The
ResponseRecorder
's newResult
method returns the recordedhttp.Response
. Tests that need to check the response's headers or trailers should callResult
and inspect the response fields instead of accessingResponseRecorder
'sHeaderMap
directly.
- net/http/httputil
-
The
ReverseProxy
implementation now responds with “502 Bad Gateway” when it cannot reach a back end; in earlier releases it responded with “500 Internal Server Error.”Both
ClientConn
andServerConn
have been documented as deprecated. They are low-level, old, and unused by Go's current HTTP stack and will no longer be updated. Programs should usehttp.Client
,http.Transport
, andhttp.Server
instead.
- net/http/pprof
-
The runtime trace HTTP handler, installed to handle the path
/debug/pprof/trace
, now accepts a fractional number in itsseconds
query parameter, allowing collection of traces for intervals smaller than one second. This is especially useful on busy servers.
- net/mail
-
The address parser now allows unescaped UTF-8 text in addresses following RFC 6532, but it does not apply any normalization to the result. For compatibility with older mail parsers, the address encoder, namely
Address
'sString
method, continues to escape all UTF-8 text following RFC 5322.The
ParseAddress
function and theAddressParser.Parse
method are stricter. They used to ignore any characters following an e-mail address, but will now return an error for anything other than whitespace.
- net/url
-
The
URL
's newForceQuery
field records whether the URL must have a query string, in order to distinguish URLs without query strings (like/search
) from URLs with empty query strings (like/search?
).
- os
-
IsExist
now returns true forsyscall.ENOTEMPTY
, on systems where that error exists.On Windows,
Remove
now removes read-only files when possible, making the implementation behave as on non-Windows systems.
- os/exec
-
As part of the introduction of context, the new constructor
CommandContext
is likeCommand
but includes a context that can be used to cancel the command execution.
- os/user
-
The
Current
function is now implemented even when cgo is not available.The new
Group
type, along with the lookup functionsLookupGroup
andLookupGroupId
and the new fieldGroupIds
in theUser
struct, provides access to system-specific user group information.
- reflect
-
Although
Value
'sField
method has always been documented to panic if the given field numberi
is out of range, it has instead silently returned a zeroValue
. Go 1.7 changes the method to behave as documented.The new
StructOf
function constructs a struct type at run time. It completes the set of type constructors, joiningArrayOf
,ChanOf
,FuncOf
,MapOf
,PtrTo
, andSliceOf
.StructTag
's new methodLookup
is likeGet
but distinguishes the tag not containing the given key from the tag associating an empty string with the given key.The
Method
andNumMethod
methods ofType
andValue
no longer return or count unexported methods.
- strings
-
In previous releases of Go, if
Reader
'sRead
method were asked for zero bytes with no data remaining, it would return a count of 0 and no error. Now it returns a count of 0 and the errorio.EOF
.The
Reader
type has a new methodReset
to allow reuse of aReader
.
- time
-
Duration
's time.Duration.String method now reports the zero duration as"0s"
, not"0"
.ParseDuration
continues to accept both forms.The method call
time.Local.String()
now returns"Local"
on all systems; in earlier releases, it returned an empty string on Windows.The time zone database in
$GOROOT/lib/time
has been updated to IANA release 2016d. This fallback database is only used when the system time zone database cannot be found, for example on Windows. The Windows time zone abbreviation list has also been updated.
- syscall
-
On Linux, the
SysProcAttr
struct (as used inos/exec.Cmd
'sSysProcAttr
field) has a newUnshareflags
field. If the field is nonzero, the child process created byForkExec
(as used inexec.Cmd
'sRun
method) will call the unshare(2) system call before executing the new program.
- unicode
-
The
unicode
package and associated support throughout the system has been upgraded from version 8.0 to Unicode 9.0.
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题意: 有n门考试,每门考试都有两个时间,存在几门考试时间冲突,求考完所有的考试,所用的最后时间的最小值 解析: 对于时间冲突的考试 就是一个联通块 把每个考试看作边,两个时间看作点,那么时间冲突的考 ...
- 新版POI如何获取日期类型的cell的值
使用POI读取Excel值的同学,一定为日期类型抓狂过! POI对单元格日期处理很弱,没有针对的类型,日期类型取出来的也是一个double值,所以同样作为数值类型.即使使用cell.setCellTy ...
- 【题解】Luogu P2047 社交网络总结 (Floyd算法,最短路计数)
题目描述 在社交网络(social network)的研究中,我们常常使用图论概念去解释一些社会现象.不妨看这样的一个问题.在一个社交圈子里有n个人,人与人之间有不同程度的关系.我 们将这个关系网络对 ...
- Crash dump进程信息
linux下 比较简单,这里不在说明, windows下 相对复杂一点,用SetUnhandledExceptionFilter 来捕获 MiniDumpWriteDump 来写dmp文件,这种方法还 ...