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37 lines
1.1 KiB
Go
37 lines
1.1 KiB
Go
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// Copyright (c) Tailscale Inc & AUTHORS
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// SPDX-License-Identifier: BSD-3-Clause
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package syncs
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// TODO(raggi): this implementation is still imperfect as it will still result
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// in cross CPU sharing periodically, we instead really want a per-CPU shard
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// key, but the limitations of calling platform code make reaching for even the
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// getcpu vdso very painful. See https://github.com/golang/go/issues/18802, and
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// hopefully one day we can replace with a primitive that falls out of that
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// work.
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// ShardValue contains a value sharded over a set of shards.
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// In order to be useful, T should be aligned to cache lines.
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// Users must organize that usage in One and All is concurrency safe.
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// The zero value is not safe for use; use [NewShardValue].
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type ShardValue[T any] struct {
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shards []T
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//lint:ignore U1000 unused under tailscale_go builds.
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pool shardValuePool
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}
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// Len returns the number of shards.
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func (sp *ShardValue[T]) Len() int {
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return len(sp.shards)
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}
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// All yields a pointer to the value in each shard.
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func (sp *ShardValue[T]) All(yield func(*T) bool) {
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for i := range sp.shards {
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if !yield(&sp.shards[i]) {
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return
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}
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}
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}
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