51 lines
1.5 KiB
Go
51 lines
1.5 KiB
Go
// 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/gohacks"
|
|
"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.
|
|
gohacks.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
|
|
}
|