atomicbitops package cleanups

- Redocument memory ordering from "no ordering" to "acquire-release". (No
  functional change: both LOCK WHATEVER on x86, and LDAXR/STLXR loops on ARM64,
  already have this property.)

- Remove IncUnlessZeroInt32 and DecUnlessOneInt32, which were only faster than
  the equivalent loops using sync/atomic before the Go compiler inlined
  non-unsafe.Pointer atomics many releases ago.

PiperOrigin-RevId: 295811743

1 files changed, 47 insertions, 0 deletions

diff --git a/pkg/atomicbitops/atomicbitops.go b/pkg/atomicbitops/atomicbitops.go
new file mode 100644
index 000000000..1be081719
--- /dev/null
+++ b/pkg/atomicbitops/atomicbitops.go
@@ -0,0 +1,47 @@
+// Copyright 2018 The gVisor Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// +build amd64 arm64
+
+// Package atomicbitops provides extensions to the sync/atomic package.
+//
+// All read-modify-write operations implemented by this package have
+// acquire-release memory ordering (like sync/atomic).
+package atomicbitops
+
+// AndUint32 atomically applies bitwise AND operation to *addr with val.
+func AndUint32(addr *uint32, val uint32)
+
+// OrUint32 atomically applies bitwise OR operation to *addr with val.
+func OrUint32(addr *uint32, val uint32)
+
+// XorUint32 atomically applies bitwise XOR operation to *addr with val.
+func XorUint32(addr *uint32, val uint32)
+
+// CompareAndSwapUint32 is like sync/atomic.CompareAndSwapUint32, but returns
+// the value previously stored at addr.
+func CompareAndSwapUint32(addr *uint32, old, new uint32) uint32
+
+// AndUint64 atomically applies bitwise AND operation to *addr with val.
+func AndUint64(addr *uint64, val uint64)
+
+// OrUint64 atomically applies bitwise OR operation to *addr with val.
+func OrUint64(addr *uint64, val uint64)
+
+// XorUint64 atomically applies bitwise XOR operation to *addr with val.
+func XorUint64(addr *uint64, val uint64)
+
+// CompareAndSwapUint64 is like sync/atomic.CompareAndSwapUint64, but returns
+// the value previously stored at addr.
+func CompareAndSwapUint64(addr *uint64, old, new uint64) uint64