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// Copyright 2019 The gVisor Authors.
//
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// Package seqatomic doesn't exist. This file must be instantiated using the
// go_template_instance rule in tools/go_generics/defs.bzl.
package seqatomic
import (
"unsafe"
"gvisor.dev/gvisor/pkg/sync"
)
// Value is a required type parameter.
type Value struct{}
// SeqAtomicLoad returns a copy of *ptr, ensuring that the read does not race
// with any writer critical sections in seq.
//
//go:nosplit
func SeqAtomicLoad(seq *sync.SeqCount, ptr *Value) Value {
for {
if val, ok := SeqAtomicTryLoad(seq, seq.BeginRead(), ptr); ok {
return val
}
}
}
// SeqAtomicTryLoad returns a copy of *ptr while in a reader critical section
// in seq initiated by a call to seq.BeginRead() that returned epoch. If the
// read would race with a writer critical section, SeqAtomicTryLoad returns
// (unspecified, false).
//
//go:nosplit
func SeqAtomicTryLoad(seq *sync.SeqCount, epoch sync.SeqCountEpoch, ptr *Value) (val Value, ok bool) {
if sync.RaceEnabled {
// runtime.RaceDisable() doesn't actually stop the race detector, so it
// can't help us here. Instead, call runtime.memmove directly, which is
// not instrumented by the race detector.
sync.Memmove(unsafe.Pointer(&val), unsafe.Pointer(ptr), unsafe.Sizeof(val))
} else {
// This is ~40% faster for short reads than going through memmove.
val = *ptr
}
ok = seq.ReadOk(epoch)
return
}
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