67 lines
2.0 KiB
Go
67 lines
2.0 KiB
Go
// Copyright 2019 The gVisor Authors.
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//
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// Package template doesn't exist. This file must be instantiated using the
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// go_template_instance rule in tools/go_generics/defs.bzl.
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package template
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import (
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"fmt"
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"reflect"
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"strings"
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"unsafe"
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"gvisor.dev/gvisor/pkg/sync"
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)
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// Value is a required type parameter.
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//
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// Value must not contain any pointers, including interface objects, function
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// objects, slices, maps, channels, unsafe.Pointer, and arrays or structs
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// containing any of the above. An init() function will panic if this property
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// does not hold.
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type Value struct{}
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// SeqAtomicLoad returns a copy of *ptr, ensuring that the read does not race
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// with any writer critical sections in seq.
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//
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//go:nosplit
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func SeqAtomicLoad(seq *sync.SeqCount, ptr *Value) Value {
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for {
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if val, ok := SeqAtomicTryLoad(seq, seq.BeginRead(), ptr); ok {
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return val
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}
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}
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}
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// SeqAtomicTryLoad returns a copy of *ptr while in a reader critical section
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// in seq initiated by a call to seq.BeginRead() that returned epoch. If the
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// read would race with a writer critical section, SeqAtomicTryLoad returns
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// (unspecified, false).
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//
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//go:nosplit
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func SeqAtomicTryLoad(seq *sync.SeqCount, epoch sync.SeqCountEpoch, ptr *Value) (val Value, ok bool) {
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if sync.RaceEnabled {
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// runtime.RaceDisable() doesn't actually stop the race detector, so it
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// can't help us here. Instead, call runtime.memmove directly, which is
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// not instrumented by the race detector.
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sync.Memmove(unsafe.Pointer(&val), unsafe.Pointer(ptr), unsafe.Sizeof(val))
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} else {
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// This is ~40% faster for short reads than going through memmove.
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val = *ptr
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}
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ok = seq.ReadOk(epoch)
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return
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}
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func init() {
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var val Value
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typ := reflect.TypeOf(val)
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name := typ.Name()
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if ptrs := sync.PointersInType(typ, name); len(ptrs) != 0 {
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panic(fmt.Sprintf("SeqAtomicLoad<%s> is invalid since values %s of type %s contain pointers:\n%s", typ, name, typ, strings.Join(ptrs, "\n")))
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}
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}
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