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609 lines
23 KiB
609 lines
23 KiB
<!--{
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"Title": "Go 1.3 Release Notes",
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"Path": "/doc/go1.3",
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"Template": true
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}-->
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<h2 id="introduction">Introduction to Go 1.3</h2>
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<p>
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The latest Go release, version 1.3, arrives six months after 1.2,
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and contains no language changes.
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It focuses primarily on implementation work, providing
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precise garbage collection,
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a major refactoring of the compiler toolchain that results in
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faster builds, especially for large projects,
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significant performance improvements across the board,
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and support for DragonFly BSD, Solaris, Plan 9 and Google's Native Client architecture (NaCl).
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It also has an important refinement to the memory model regarding synchronization.
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As always, Go 1.3 keeps the <a href="/doc/go1compat.html">promise
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of compatibility</a>,
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and almost everything
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will continue to compile and run without change when moved to 1.3.
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</p>
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<h2 id="os">Changes to the supported operating systems and architectures</h2>
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<h3 id="win2000">Removal of support for Windows 2000</h3>
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<p>
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Microsoft stopped supporting Windows 2000 in 2010.
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Since it has <a href="https://codereview.appspot.com/74790043">implementation difficulties</a>
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regarding exception handling (signals in Unix terminology),
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as of Go 1.3 it is not supported by Go either.
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</p>
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<h3 id="dragonfly">Support for DragonFly BSD</h3>
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<p>
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Go 1.3 now includes experimental support for DragonFly BSD on the <code>amd64</code> (64-bit x86) and <code>386</code> (32-bit x86) architectures.
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It uses DragonFly BSD 3.6 or above.
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</p>
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<h3 id="freebsd">Support for FreeBSD</h3>
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<p>
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It was not announced at the time, but since the release of Go 1.2, support for Go on FreeBSD
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requires FreeBSD 8 or above.
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</p>
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<p>
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As of Go 1.3, support for Go on FreeBSD requires that the kernel be compiled with the
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<code>COMPAT_FREEBSD32</code> flag configured.
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</p>
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<p>
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In concert with the switch to EABI syscalls for ARM platforms, Go 1.3 will run only on FreeBSD 10.
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The x86 platforms, 386 and amd64, are unaffected.
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</p>
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<h3 id="nacl">Support for Native Client</h3>
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<p>
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Support for the Native Client virtual machine architecture has returned to Go with the 1.3 release.
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It runs on the 32-bit Intel architectures (<code>GOARCH=386</code>) and also on 64-bit Intel, but using
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32-bit pointers (<code>GOARCH=amd64p32</code>).
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There is not yet support for Native Client on ARM.
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Note that this is Native Client (NaCl), not Portable Native Client (PNaCl).
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Details about Native Client are <a href="https://developers.google.com/native-client/dev/">here</a>;
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how to set up the Go version is described <a href="//golang.org/wiki/NativeClient">here</a>.
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</p>
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<h3 id="netbsd">Support for NetBSD</h3>
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<p>
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As of Go 1.3, support for Go on NetBSD requires NetBSD 6.0 or above.
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</p>
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<h3 id="openbsd">Support for OpenBSD</h3>
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<p>
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As of Go 1.3, support for Go on OpenBSD requires OpenBSD 5.5 or above.
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</p>
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<h3 id="plan9">Support for Plan 9</h3>
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<p>
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Go 1.3 now includes experimental support for Plan 9 on the <code>386</code> (32-bit x86) architecture.
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It requires the <code>Tsemacquire</code> syscall, which has been in Plan 9 since June, 2012.
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</p>
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<h3 id="solaris">Support for Solaris</h3>
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<p>
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Go 1.3 now includes experimental support for Solaris on the <code>amd64</code> (64-bit x86) architecture.
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It requires illumos, Solaris 11 or above.
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</p>
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<h2 id="memory">Changes to the memory model</h2>
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<p>
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The Go 1.3 memory model <a href="https://codereview.appspot.com/75130045">adds a new rule</a>
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concerning sending and receiving on buffered channels,
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to make explicit that a buffered channel can be used as a simple
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semaphore, using a send into the
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channel to acquire and a receive from the channel to release.
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This is not a language change, just a clarification about an expected property of communication.
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</p>
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<h2 id="impl">Changes to the implementations and tools</h2>
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<h3 id="stacks">Stack</h3>
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<p>
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Go 1.3 has changed the implementation of goroutine stacks away from the old,
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"segmented" model to a contiguous model.
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When a goroutine needs more stack
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than is available, its stack is transferred to a larger single block of memory.
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The overhead of this transfer operation amortizes well and eliminates the old "hot spot"
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problem when a calculation repeatedly steps across a segment boundary.
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Details including performance numbers are in this
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<a href="//golang.org/s/contigstacks">design document</a>.
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</p>
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<h3 id="garbage_collector">Changes to the garbage collector</h3>
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<p>
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For a while now, the garbage collector has been <em>precise</em> when examining
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values in the heap; the Go 1.3 release adds equivalent precision to values on the stack.
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This means that a non-pointer Go value such as an integer will never be mistaken for a
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pointer and prevent unused memory from being reclaimed.
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</p>
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<p>
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Starting with Go 1.3, the runtime assumes that values with pointer type
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contain pointers and other values do not.
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This assumption is fundamental to the precise behavior of both stack expansion
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and garbage collection.
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Programs that use <a href="/pkg/unsafe/">package unsafe</a>
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to store integers in pointer-typed values are illegal and will crash if the runtime detects the behavior.
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Programs that use <a href="/pkg/unsafe/">package unsafe</a> to store pointers
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in integer-typed values are also illegal but more difficult to diagnose during execution.
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Because the pointers are hidden from the runtime, a stack expansion or garbage collection
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may reclaim the memory they point at, creating
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<a href="//en.wikipedia.org/wiki/Dangling_pointer">dangling pointers</a>.
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</p>
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<p>
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<em>Updating</em>: Code that uses <code>unsafe.Pointer</code> to convert
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an integer-typed value held in memory into a pointer is illegal and must be rewritten.
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Such code can be identified by <code>go vet</code>.
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</p>
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<h3 id="map">Map iteration</h3>
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<p>
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Iterations over small maps no longer happen in a consistent order.
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Go 1 defines that “<a href="//golang.org/ref/spec#For_statements">The iteration order over maps
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is not specified and is not guaranteed to be the same from one iteration to the next.</a>”
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To keep code from depending on map iteration order,
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Go 1.0 started each map iteration at a random index in the map.
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A new map implementation introduced in Go 1.1 neglected to randomize
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iteration for maps with eight or fewer entries, although the iteration order
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can still vary from system to system.
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This has allowed people to write Go 1.1 and Go 1.2 programs that
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depend on small map iteration order and therefore only work reliably on certain systems.
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Go 1.3 reintroduces random iteration for small maps in order to flush out these bugs.
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</p>
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<p>
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<em>Updating</em>: If code assumes a fixed iteration order for small maps,
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it will break and must be rewritten not to make that assumption.
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Because only small maps are affected, the problem arises most often in tests.
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</p>
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<h3 id="liblink">The linker</h3>
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<p>
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As part of the general <a href="//golang.org/s/go13linker">overhaul</a> to
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the Go linker, the compilers and linkers have been refactored.
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The linker is still a C program, but now the instruction selection phase that
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was part of the linker has been moved to the compiler through the creation of a new
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library called <code>liblink</code>.
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By doing instruction selection only once, when the package is first compiled,
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this can speed up compilation of large projects significantly.
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</p>
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<p>
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<em>Updating</em>: Although this is a major internal change, it should have no
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effect on programs.
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</p>
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<h3 id="gccgo">Status of gccgo</h3>
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<p>
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GCC release 4.9 will contain the Go 1.2 (not 1.3) version of gccgo.
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The release schedules for the GCC and Go projects do not coincide,
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which means that 1.3 will be available in the development branch but
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that the next GCC release, 4.10, will likely have the Go 1.4 version of gccgo.
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</p>
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<h3 id="gocmd">Changes to the go command</h3>
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<p>
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The <a href="/cmd/go/"><code>cmd/go</code></a> command has several new
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features.
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The <a href="/cmd/go/"><code>go run</code></a> and
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<a href="/cmd/go/"><code>go test</code></a> subcommands
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support a new <code>-exec</code> option to specify an alternate
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way to run the resulting binary.
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Its immediate purpose is to support NaCl.
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</p>
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<p>
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The test coverage support of the <a href="/cmd/go/"><code>go test</code></a>
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subcommand now automatically sets the coverage mode to <code>-atomic</code>
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when the race detector is enabled, to eliminate false reports about unsafe
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access to coverage counters.
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</p>
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<p>
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The <a href="/cmd/go/"><code>go test</code></a> subcommand
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now always builds the package, even if it has no test files.
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Previously, it would do nothing if no test files were present.
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</p>
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<p>
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The <a href="/cmd/go/"><code>go build</code></a> subcommand
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supports a new <code>-i</code> option to install dependencies
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of the specified target, but not the target itself.
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</p>
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<p>
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Cross compiling with <a href="/cmd/cgo/"><code>cgo</code></a> enabled
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is now supported.
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The CC_FOR_TARGET and CXX_FOR_TARGET environment
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variables are used when running all.bash to specify the cross compilers
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for C and C++ code, respectively.
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</p>
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<p>
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Finally, the go command now supports packages that import Objective-C
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files (suffixed <code>.m</code>) through cgo.
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</p>
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<h3 id="cgo">Changes to cgo</h3>
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<p>
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The <a href="/cmd/cgo/"><code>cmd/cgo</code></a> command,
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which processes <code>import "C"</code> declarations in Go packages,
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has corrected a serious bug that may cause some packages to stop compiling.
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Previously, all pointers to incomplete struct types translated to the Go type <code>*[0]byte</code>,
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with the effect that the Go compiler could not diagnose passing one kind of struct pointer
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to a function expecting another.
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Go 1.3 corrects this mistake by translating each different
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incomplete struct to a different named type.
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</p>
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<p>
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Given the C declaration <code>typedef struct S T</code> for an incomplete <code>struct S</code>,
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some Go code used this bug to refer to the types <code>C.struct_S</code> and <code>C.T</code> interchangeably.
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Cgo now explicitly allows this use, even for completed struct types.
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However, some Go code also used this bug to pass (for example) a <code>*C.FILE</code>
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from one package to another.
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This is not legal and no longer works: in general Go packages
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should avoid exposing C types and names in their APIs.
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</p>
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<p>
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<em>Updating</em>: Code confusing pointers to incomplete types or
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passing them across package boundaries will no longer compile
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and must be rewritten.
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If the conversion is correct and must be preserved,
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use an explicit conversion via <a href="/pkg/unsafe/#Pointer"><code>unsafe.Pointer</code></a>.
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</p>
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<h3 id="swig">SWIG 3.0 required for programs that use SWIG</h3>
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<p>
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For Go programs that use SWIG, SWIG version 3.0 is now required.
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The <a href="/cmd/go"><code>cmd/go</code></a> command will now link the
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SWIG generated object files directly into the binary, rather than
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building and linking with a shared library.
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</p>
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<h3 id="gc_flag">Command-line flag parsing</h3>
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<p>
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In the gc toolchain, the assemblers now use the
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same command-line flag parsing rules as the Go flag package, a departure
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from the traditional Unix flag parsing.
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This may affect scripts that invoke the tool directly.
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For example,
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<code>go tool 6a -SDfoo</code> must now be written
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<code>go tool 6a -S -D foo</code>.
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(The same change was made to the compilers and linkers in <a href="/doc/go1.1#gc_flag">Go 1.1</a>.)
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</p>
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<h3 id="godoc">Changes to godoc</h3>
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<p>
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When invoked with the <code>-analysis</code> flag,
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<a href="//godoc.org/golang.org/x/tools/cmd/godoc">godoc</a>
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now performs sophisticated <a href="/lib/godoc/analysis/help.html">static
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analysis</a> of the code it indexes.
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The results of analysis are presented in both the source view and the
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package documentation view, and include the call graph of each package
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and the relationships between
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definitions and references,
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types and their methods,
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interfaces and their implementations,
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send and receive operations on channels,
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functions and their callers, and
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call sites and their callees.
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</p>
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<h3 id="misc">Miscellany</h3>
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<p>
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The program <code>misc/benchcmp</code> that compares
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performance across benchmarking runs has been rewritten.
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Once a shell and awk script in the main repository, it is now a Go program in the <code>go.tools</code> repo.
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Documentation is <a href="//godoc.org/golang.org/x/tools/cmd/benchcmp">here</a>.
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</p>
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<p>
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For the few of us that build Go distributions, the tool <code>misc/dist</code> has been
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moved and renamed; it now lives in <code>misc/makerelease</code>, still in the main repository.
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</p>
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<h2 id="performance">Performance</h2>
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<p>
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The performance of Go binaries for this release has improved in many cases due to changes
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in the runtime and garbage collection, plus some changes to libraries.
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Significant instances include:
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</p>
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<ul>
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<li>
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The runtime handles defers more efficiently, reducing the memory footprint by about two kilobytes
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per goroutine that calls defer.
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</li>
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<li>
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The garbage collector has been sped up, using a concurrent sweep algorithm,
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better parallelization, and larger pages.
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The cumulative effect can be a 50-70% reduction in collector pause time.
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</li>
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<li>
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The race detector (see <a href="/doc/articles/race_detector.html">this guide</a>)
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is now about 40% faster.
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</li>
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<li>
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The regular expression package <a href="/pkg/regexp/"><code>regexp</code></a>
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is now significantly faster for certain simple expressions due to the implementation of
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a second, one-pass execution engine.
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The choice of which engine to use is automatic;
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the details are hidden from the user.
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</li>
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</ul>
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<p>
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Also, the runtime now includes in stack dumps how long a goroutine has been blocked,
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which can be useful information when debugging deadlocks or performance issues.
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</p>
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<h2 id="library">Changes to the standard library</h2>
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<h3 id="new_packages">New packages</h3>
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<p>
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A new package <a href="/pkg/debug/plan9obj/"><code>debug/plan9obj</code></a> was added to the standard library.
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It implements access to Plan 9 <a href="https://9p.io/magic/man2html/6/a.out">a.out</a> object files.
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</p>
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|
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<h3 id="major_library_changes">Major changes to the library</h3>
|
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|
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<p>
|
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A previous bug in <a href="/pkg/crypto/tls/"><code>crypto/tls</code></a>
|
|
made it possible to skip verification in TLS inadvertently.
|
|
In Go 1.3, the bug is fixed: one must specify either ServerName or
|
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InsecureSkipVerify, and if ServerName is specified it is enforced.
|
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This may break existing code that incorrectly depended on insecure
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behavior.
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</p>
|
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|
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<p>
|
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There is an important new type added to the standard library: <a href="/pkg/sync/#Pool"><code>sync.Pool</code></a>.
|
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It provides an efficient mechanism for implementing certain types of caches whose memory
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can be reclaimed automatically by the system.
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</p>
|
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|
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<p>
|
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The <a href="/pkg/testing/"><code>testing</code></a> package's benchmarking helper,
|
|
<a href="/pkg/testing/#B"><code>B</code></a>, now has a
|
|
<a href="/pkg/testing/#B.RunParallel"><code>RunParallel</code></a> method
|
|
to make it easier to run benchmarks that exercise multiple CPUs.
|
|
</p>
|
|
|
|
<p>
|
|
<em>Updating</em>: The crypto/tls fix may break existing code, but such
|
|
code was erroneous and should be updated.
|
|
</p>
|
|
|
|
<h3 id="minor_library_changes">Minor changes to the library</h3>
|
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|
|
<p>
|
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The following list summarizes a number of minor changes to the library, mostly additions.
|
|
See the relevant package documentation for more information about each change.
|
|
</p>
|
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|
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<ul>
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<li> In the <a href="/pkg/crypto/tls/"><code>crypto/tls</code></a> package,
|
|
a new <a href="/pkg/crypto/tls/#DialWithDialer"><code>DialWithDialer</code></a>
|
|
function lets one establish a TLS connection using an existing dialer, making it easier
|
|
to control dial options such as timeouts.
|
|
The package also now reports the TLS version used by the connection in the
|
|
<a href="/pkg/crypto/tls/#ConnectionState"><code>ConnectionState</code></a>
|
|
struct.
|
|
</li>
|
|
|
|
<li> The <a href="/pkg/crypto/x509/#CreateCertificate"><code>CreateCertificate</code></a>
|
|
function of the <a href="/pkg/crypto/tls/"><code>crypto/tls</code></a> package
|
|
now supports parsing (and elsewhere, serialization) of PKCS #10 certificate
|
|
signature requests.
|
|
</li>
|
|
|
|
<li>
|
|
The formatted print functions of the <code>fmt</code> package now define <code>%F</code>
|
|
as a synonym for <code>%f</code> when printing floating-point values.
|
|
</li>
|
|
|
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<li>
|
|
The <a href="/pkg/math/big/"><code>math/big</code></a> package's
|
|
<a href="/pkg/math/big/#Int"><code>Int</code></a> and
|
|
<a href="/pkg/math/big/#Rat"><code>Rat</code></a> types
|
|
now implement
|
|
<a href="/pkg/encoding/#TextMarshaler"><code>encoding.TextMarshaler</code></a> and
|
|
<a href="/pkg/encoding/#TextUnmarshaler"><code>encoding.TextUnmarshaler</code></a>.
|
|
</li>
|
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|
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<li>
|
|
The complex power function, <a href="/pkg/math/cmplx/#Pow"><code>Pow</code></a>,
|
|
now specifies the behavior when the first argument is zero.
|
|
It was undefined before.
|
|
The details are in the <a href="/pkg/math/cmplx/#Pow">documentation for the function</a>.
|
|
</li>
|
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|
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<li>
|
|
The <a href="/pkg/net/http/"><code>net/http</code></a> package now exposes the
|
|
properties of a TLS connection used to make a client request in the new
|
|
<a href="/pkg/net/http/#Response"><code>Response.TLS</code></a> field.
|
|
</li>
|
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|
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<li>
|
|
The <a href="/pkg/net/http/"><code>net/http</code></a> package now
|
|
allows setting an optional server error logger
|
|
with <a href="/pkg/net/http/#Server"><code>Server.ErrorLog</code></a>.
|
|
The default is still that all errors go to stderr.
|
|
</li>
|
|
|
|
<li>
|
|
The <a href="/pkg/net/http/"><code>net/http</code></a> package now
|
|
supports disabling HTTP keep-alive connections on the server
|
|
with <a href="/pkg/net/http/#Server.SetKeepAlivesEnabled"><code>Server.SetKeepAlivesEnabled</code></a>.
|
|
The default continues to be that the server does keep-alive (reuses
|
|
connections for multiple requests) by default.
|
|
Only resource-constrained servers or those in the process of graceful
|
|
shutdown will want to disable them.
|
|
</li>
|
|
|
|
<li>
|
|
The <a href="/pkg/net/http/"><code>net/http</code></a> package adds an optional
|
|
<a href="/pkg/net/http/#Transport"><code>Transport.TLSHandshakeTimeout</code></a>
|
|
setting to cap the amount of time HTTP client requests will wait for
|
|
TLS handshakes to complete.
|
|
It's now also set by default
|
|
on <a href="/pkg/net/http#DefaultTransport"><code>DefaultTransport</code></a>.
|
|
</li>
|
|
|
|
<li>
|
|
The <a href="/pkg/net/http/"><code>net/http</code></a> package's
|
|
<a href="/pkg/net/http/#DefaultTransport"><code>DefaultTransport</code></a>,
|
|
used by the HTTP client code, now
|
|
enables <a href="http://en.wikipedia.org/wiki/Keepalive#TCP_keepalive">TCP
|
|
keep-alives</a> by default.
|
|
Other <a href="/pkg/net/http/#Transport"><code>Transport</code></a>
|
|
values with a nil <code>Dial</code> field continue to function the same
|
|
as before: no TCP keep-alives are used.
|
|
</li>
|
|
|
|
<li>
|
|
The <a href="/pkg/net/http/"><code>net/http</code></a> package
|
|
now enables <a href="http://en.wikipedia.org/wiki/Keepalive#TCP_keepalive">TCP
|
|
keep-alives</a> for incoming server requests when
|
|
<a href="/pkg/net/http/#ListenAndServe"><code>ListenAndServe</code></a>
|
|
or
|
|
<a href="/pkg/net/http/#ListenAndServeTLS"><code>ListenAndServeTLS</code></a>
|
|
are used.
|
|
When a server is started otherwise, TCP keep-alives are not enabled.
|
|
</li>
|
|
|
|
<li>
|
|
The <a href="/pkg/net/http/"><code>net/http</code></a> package now
|
|
provides an
|
|
optional <a href="/pkg/net/http/#Server"><code>Server.ConnState</code></a>
|
|
callback to hook various phases of a server connection's lifecycle
|
|
(see <a href="/pkg/net/http/#ConnState"><code>ConnState</code></a>).
|
|
This can be used to implement rate limiting or graceful shutdown.
|
|
</li>
|
|
|
|
<li>
|
|
The <a href="/pkg/net/http/"><code>net/http</code></a> package's HTTP
|
|
client now has an
|
|
optional <a href="/pkg/net/http/#Client"><code>Client.Timeout</code></a>
|
|
field to specify an end-to-end timeout on requests made using the
|
|
client.
|
|
</li>
|
|
|
|
<li>
|
|
The <a href="/pkg/net/http/"><code>net/http</code></a> package's
|
|
<a href="/pkg/net/http/#Request.ParseMultipartForm"><code>Request.ParseMultipartForm</code></a>
|
|
method will now return an error if the body's <code>Content-Type</code>
|
|
is not <code>multipart/form-data</code>.
|
|
Prior to Go 1.3 it would silently fail and return <code>nil</code>.
|
|
Code that relies on the previous behavior should be updated.
|
|
</li>
|
|
|
|
<li> In the <a href="/pkg/net/"><code>net</code></a> package,
|
|
the <a href="/pkg/net/#Dialer"><code>Dialer</code></a> struct now
|
|
has a <code>KeepAlive</code> option to specify a keep-alive period for the connection.
|
|
</li>
|
|
|
|
<li>
|
|
The <a href="/pkg/net/http/"><code>net/http</code></a> package's
|
|
<a href="/pkg/net/http/#Transport"><code>Transport</code></a>
|
|
now closes <a href="/pkg/net/http/#Request"><code>Request.Body</code></a>
|
|
consistently, even on error.
|
|
</li>
|
|
|
|
<li>
|
|
The <a href="/pkg/os/exec/"><code>os/exec</code></a> package now implements
|
|
what the documentation has always said with regard to relative paths for the binary.
|
|
In particular, it only calls <a href="/pkg/os/exec/#LookPath"><code>LookPath</code></a>
|
|
when the binary's file name contains no path separators.
|
|
</li>
|
|
|
|
<li>
|
|
The <a href="/pkg/reflect/#Value.SetMapIndex"><code>SetMapIndex</code></a>
|
|
function in the <a href="/pkg/reflect/"><code>reflect</code></a> package
|
|
no longer panics when deleting from a <code>nil</code> map.
|
|
</li>
|
|
|
|
<li>
|
|
If the main goroutine calls
|
|
<a href="/pkg/runtime/#Goexit"><code>runtime.Goexit</code></a>
|
|
and all other goroutines finish execution, the program now always crashes,
|
|
reporting a detected deadlock.
|
|
Earlier versions of Go handled this situation inconsistently: most instances
|
|
were reported as deadlocks, but some trivial cases exited cleanly instead.
|
|
</li>
|
|
|
|
<li>
|
|
The runtime/debug package now has a new function
|
|
<a href="/pkg/runtime/debug/#WriteHeapDump"><code>debug.WriteHeapDump</code></a>
|
|
that writes out a description of the heap.
|
|
</li>
|
|
|
|
<li>
|
|
The <a href="/pkg/strconv/#CanBackquote"><code>CanBackquote</code></a>
|
|
function in the <a href="/pkg/strconv/"><code>strconv</code></a> package
|
|
now considers the <code>DEL</code> character, <code>U+007F</code>, to be
|
|
non-printing.
|
|
</li>
|
|
|
|
<li>
|
|
The <a href="/pkg/syscall/"><code>syscall</code></a> package now provides
|
|
<a href="/pkg/syscall/#SendmsgN"><code>SendmsgN</code></a>
|
|
as an alternate version of
|
|
<a href="/pkg/syscall/#Sendmsg"><code>Sendmsg</code></a>
|
|
that returns the number of bytes written.
|
|
</li>
|
|
|
|
<li>
|
|
On Windows, the <a href="/pkg/syscall/"><code>syscall</code></a> package now
|
|
supports the cdecl calling convention through the addition of a new function
|
|
<a href="/pkg/syscall/#NewCallbackCDecl"><code>NewCallbackCDecl</code></a>
|
|
alongside the existing function
|
|
<a href="/pkg/syscall/#NewCallback"><code>NewCallback</code></a>.
|
|
</li>
|
|
|
|
<li>
|
|
The <a href="/pkg/testing/"><code>testing</code></a> package now
|
|
diagnoses tests that call <code>panic(nil)</code>, which are almost always erroneous.
|
|
Also, tests now write profiles (if invoked with profiling flags) even on failure.
|
|
</li>
|
|
|
|
<li>
|
|
The <a href="/pkg/unicode/"><code>unicode</code></a> package and associated
|
|
support throughout the system has been upgraded from
|
|
Unicode 6.2.0 to <a href="http://www.unicode.org/versions/Unicode6.3.0/">Unicode 6.3.0</a>.
|
|
</li>
|
|
|
|
</ul>
|