diff options
author | Adin Scannell <ascannell@google.com> | 2019-11-21 11:29:49 -0800 |
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committer | gVisor bot <gvisor-bot@google.com> | 2019-11-21 11:41:30 -0800 |
commit | c0f89eba6ebdec08460bd796fc62d6aef674d141 (patch) | |
tree | 38b35320dc70d55e0b83d221d5c45a404f8a6683 /pkg/syncutil/seqatomic_unsafe.go | |
parent | b6a00aa375e674617f1914b90db5ddb222b5a04e (diff) |
Import and structure cleanup.
PiperOrigin-RevId: 281795269
Diffstat (limited to 'pkg/syncutil/seqatomic_unsafe.go')
-rw-r--r-- | pkg/syncutil/seqatomic_unsafe.go | 72 |
1 files changed, 72 insertions, 0 deletions
diff --git a/pkg/syncutil/seqatomic_unsafe.go b/pkg/syncutil/seqatomic_unsafe.go new file mode 100644 index 000000000..cb6d2eb22 --- /dev/null +++ b/pkg/syncutil/seqatomic_unsafe.go @@ -0,0 +1,72 @@ +// 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 template doesn't exist. This file must be instantiated using the +// go_template_instance rule in tools/go_generics/defs.bzl. +package template + +import ( + "fmt" + "reflect" + "strings" + "unsafe" + + "gvisor.dev/gvisor/pkg/syncutil" +) + +// Value is a required type parameter. +// +// Value must not contain any pointers, including interface objects, function +// objects, slices, maps, channels, unsafe.Pointer, and arrays or structs +// containing any of the above. An init() function will panic if this property +// does not hold. +type Value struct{} + +// SeqAtomicLoad returns a copy of *ptr, ensuring that the read does not race +// with any writer critical sections in sc. +func SeqAtomicLoad(sc *syncutil.SeqCount, ptr *Value) Value { + // This function doesn't use SeqAtomicTryLoad because doing so is + // measurably, significantly (~20%) slower; Go is awful at inlining. + var val Value + for { + epoch := sc.BeginRead() + if syncutil.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. + syncutil.Memmove(unsafe.Pointer(&val), unsafe.Pointer(ptr), unsafe.Sizeof(val)) + } else { + // This is ~40% faster for short reads than going through memmove. + val = *ptr + } + if sc.ReadOk(epoch) { + break + } + } + return val +} + +// SeqAtomicTryLoad returns a copy of *ptr while in a reader critical section +// in sc initiated by a call to sc.BeginRead() that returned epoch. If the read +// would race with a writer critical section, SeqAtomicTryLoad returns +// (unspecified, false). +func SeqAtomicTryLoad(sc *syncutil.SeqCount, epoch syncutil.SeqCountEpoch, ptr *Value) (Value, bool) { + var val Value + if syncutil.RaceEnabled { + syncutil.Memmove(unsafe.Pointer(&val), unsafe.Pointer(ptr), unsafe.Sizeof(val)) + } else { + val = *ptr + } + return val, sc.ReadOk(epoch) +} + +func init() { + var val Value + typ := reflect.TypeOf(val) + name := typ.Name() + if ptrs := syncutil.PointersInType(typ, name); len(ptrs) != 0 { + panic(fmt.Sprintf("SeqAtomicLoad<%s> is invalid since values %s of type %s contain pointers:\n%s", typ, name, typ, strings.Join(ptrs, "\n"))) + } +} |