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This adds the three functions from #56102 to the sync package. These provide a convenient API for the most common uses of sync.Once. The performance of these is comparable to direct use of sync.Once: $ go test -run ^$ -bench OnceFunc\|OnceVal -count 20 | benchstat -row .name -col /v goos: linux goarch: amd64 pkg: sync cpu: 11th Gen Intel(R) Core(TM) i7-1185G7 @ 3.00GHz │ Once │ Global │ Local │ │ sec/op │ sec/op vs base │ sec/op vs base │ OnceFunc 1.3500n ± 6% 2.7030n ± 1% +100.22% (p=0.000 n=20) 0.3935n ± 0% -70.86% (p=0.000 n=20) OnceValue 1.3155n ± 0% 2.7460n ± 1% +108.74% (p=0.000 n=20) 0.5478n ± 1% -58.35% (p=0.000 n=20) The "Once" column represents the baseline of how code would typically express these patterns using sync.Once. "Global" binds the closure returned by OnceFunc/OnceValue to global, which is how I expect these to be used most of the time. Currently, this defeats some inlining opportunities, which roughly doubles the cost over sync.Once; however, it's still *extremely* fast. Finally, "Local" binds the returned closure to a local variable. This unlocks several levels of inlining and represents pretty much the best possible case for these APIs, but is also unlikely to happen in practice. In principle the compiler could recognize that the global in the "Global" case is initialized in place and never mutated and do the same optimizations it does in the "Local" case, but it currently does not. Fixes #56102 Change-Id: If7355eccd7c8de7288d89a4282ff15ab1469e420 Reviewed-on: https://go-review.googlesource.com/c/go/+/451356 TryBot-Result: Gopher Robot <gobot@golang.org> Run-TryBot: Austin Clements <austin@google.com> Reviewed-by: Andrew Gerrand <adg@golang.org> Reviewed-by: Keith Randall <khr@google.com> Reviewed-by: Caleb Spare <cespare@gmail.com> Auto-Submit: Austin Clements <austin@google.com>
98 lines
2.4 KiB
HTML
98 lines
2.4 KiB
HTML
<!--{
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"Title": "Go 1.21 Release Notes",
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"Path": "/doc/go1.21"
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}-->
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<!--
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NOTE: In this document and others in this directory, the convention is to
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set fixed-width phrases with non-fixed-width spaces, as in
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<code>hello</code> <code>world</code>.
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Do not send CLs removing the interior tags from such phrases.
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-->
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<style>
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main ul li { margin: 0.5em 0; }
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</style>
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<h2 id="introduction">DRAFT RELEASE NOTES — Introduction to Go 1.21</h2>
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<p>
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<strong>
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Go 1.21 is not yet released. These are work-in-progress
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release notes. Go 1.21 is expected to be released in August 2023.
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</strong>
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</p>
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<h2 id="language">Changes to the language</h2>
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<p>
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TODO: complete this section
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</p>
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<h2 id="ports">Ports</h2>
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<p>
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TODO: complete this section, or delete if not needed
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</p>
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<h2 id="tools">Tools</h2>
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<h3 id="go-command">Go command</h3>
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<p>
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TODO: complete this section, or delete if not needed
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</p>
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<h2 id="runtime">Runtime</h2>
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<p>
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TODO: complete this section, or delete if not needed
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</p>
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<p><!-- https://go.dev/issue/7181 -->
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When printing very deep stacks, the runtime now prints the first 50
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(innermost) frames followed by the bottom 50 (outermost) frames,
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rather than just printing the first 100 frames. This makes it easier
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to see how deeply recursive stacks started, and is especially
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valuable for debugging stack overflows.
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</p>
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<h2 id="compiler">Compiler</h2>
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<p>
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TODO: complete this section, or delete if not needed
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</p>
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<h2 id="linker">Linker</h2>
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<p>
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TODO: complete this section, or delete if not needed
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</p>
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<h2 id="library">Core library</h2>
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<h3 id="minor_library_changes">Minor changes to the library</h3>
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<p>
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As always, there are various minor changes and updates to the library,
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made with the Go 1 <a href="/doc/go1compat">promise of compatibility</a>
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in mind.
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There are also various performance improvements, not enumerated here.
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</p>
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<p>
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TODO: complete this section
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</p>
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<dl id="sync"><dt><a href="/pkg/sync/">sync</a></dt>
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<dd>
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<p><!-- https://go.dev/issue/56102, CL 451356 -->
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The new <a href="/pkg/sync/#OnceFunc"><code>OnceFunc</code></a>,
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<a href="/pkg/sync/#OnceValue"><code>OnceValue</code></a>, and
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<a href="/pkg/sync/#OnceValues"><code>OnceValues</code></a>
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functions capture a common use of <a href="/pkg/sync/#Once">Once</a> to
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lazily initialize a value on first use.
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</p>
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</dd>
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</dl>
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