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New in Go 1 will be nanosecond precision in the result of time.Now on Linux. This will break code that stores time in external formats at microsecond precision, reads it back, and expects to get exactly the same time. Code like that can be fixed by using time.Now().Round(time.Microsecond) instead of time.Now() in those contexts. R=golang-dev, bradfitz, iant, remyoudompheng CC=golang-dev https://golang.org/cl/6903050
90 lines
3.1 KiB
HTML
90 lines
3.1 KiB
HTML
<!--{
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"Title": "Go 1.1 Release Notes",
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"Path": "/doc/go1.1",
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"Template": true
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}-->
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<h2 id="introduction">Introduction to Go 1.1</h2>
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TODO
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- overview
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- link back to Go 1 and also Go 1 Compatibility docs.
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<h2 id="language">Changes to the language</h2>
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TODO
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<h2 id="impl">Changes to the implementations and tools</h2>
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TODO: more
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<h3 id="int">Size of int on 64-bit platforms</h3>
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<p>
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The language allows the implementation to choose whether the <code>int</code> type and <code>uint</code> types are 32 or 64 bits. Previous Go implementations made <code>int</code> and <code>uint</code> 32 bits on all systems. Both the gc and gccgo implementations (TODO: check that gccgo does) <a href="http://golang.org/issue/2188">now make <code>int</code> and <code>uint</code> 64 bits on 64-bit platforms such as AMD64/x86-64</a>.
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Among other things, this enables the allocation of slices with
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more than 2 billion elements on 64-bit platforms.
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</p>
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<p>
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<em>Updating</em>:
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Most programs will be unaffected by this change.
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Because Go does not allow implicit conversions between distinct
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<a href="/ref/spec#Numeric_types">numeric types</a>,
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no programs will stop compiling due to this change.
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However, programs that contain implicit assumptions
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that <code>int</code> is only 32 bits may change behavior.
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For example, this code prints a positive number on 64-bit systems and
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a negative one on 32-bit systems:
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<pre>
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x := ^uint32(0) // x is 0xffffffff
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i := int(x) // i is -1 on 32-bit systems, 0xffffffff on 64-bit
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fmt.Println(i)
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</pre>
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<p>Portable code intending 32-bit sign extension (yielding -1 on all systems)
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would instead say:
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</p>
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<pre>
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i := int(int32(x))
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</pre>
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<h3 id="asm">Assembler</h3>
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<p>
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Due to the <a href="#int">int</a> and TODO: OTHER changes,
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the placement of function arguments on the stack has changed.
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Functions written in assembly will need to be revised at least
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to adjust frame pointer offsets.
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</p>
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<h2 id="library">Changes to the standard library</h2>
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<h3 id="debug/elf">debug/elf</h3>
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<p>
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Previous versions of the debug/elf package intentionally skipped over the first
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symbol in the ELF symbol table, since it is always an empty symbol. This symbol
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is no longer skipped since indexes into the symbol table returned by debug/elf,
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will be different to indexes into the original ELF symbol table. Any code that
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calls the debug/elf functions Symbols or ImportedSymbols may need to be
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adjusted to account for the additional symbol and the change in symbol offsets.
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</p>
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<h3 id="time">time</h3>
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<p>
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On Linux, previous versions of the time package returned times with
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microsecond precision. The Go 1.1 implementation of time on Linux now returns times with
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nanosecond precision. Code may exist that expects to be able to store
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such a time in an external format with only microsecond precision,
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read it back, and recover exactly the same time instant.
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In Go 1.1 the same time will not be recovered, since the external storage
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will have discarded nanoseconds.
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To address this case, there are two new methods of time.Time, Round and Truncate,
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that can be used to remove precision from a time before passing it to
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external storage.
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</p>
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TODO
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