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, 105 insertions, 0 deletions

diff --git a/pkg/atomicbitops/atomicbitops_noasm.go b/pkg/atomicbitops/atomicbitops_noasm.go
new file mode 100644
index 000000000..3b2898256
--- /dev/null
+++ b/pkg/atomicbitops/atomicbitops_noasm.go
@@ -0,0 +1,105 @@
+// 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
+
+import (
+	"sync/atomic"
+)
+
+func AndUint32(addr *uint32, val uint32) {
+	for {
+		o := atomic.LoadUint32(addr)
+		n := o & val
+		if atomic.CompareAndSwapUint32(addr, o, n) {
+			break
+		}
+	}
+}
+
+func OrUint32(addr *uint32, val uint32) {
+	for {
+		o := atomic.LoadUint32(addr)
+		n := o | val
+		if atomic.CompareAndSwapUint32(addr, o, n) {
+			break
+		}
+	}
+}
+
+func XorUint32(addr *uint32, val uint32) {
+	for {
+		o := atomic.LoadUint32(addr)
+		n := o ^ val
+		if atomic.CompareAndSwapUint32(addr, o, n) {
+			break
+		}
+	}
+}
+
+func CompareAndSwapUint32(addr *uint32, old, new uint32) (prev uint32) {
+	for {
+		prev = atomic.LoadUint32(addr)
+		if prev != old {
+			return
+		}
+		if atomic.CompareAndSwapUint32(addr, old, new) {
+			return
+		}
+	}
+}
+
+func AndUint64(addr *uint64, val uint64) {
+	for {
+		o := atomic.LoadUint64(addr)
+		n := o & val
+		if atomic.CompareAndSwapUint64(addr, o, n) {
+			break
+		}
+	}
+}
+
+func OrUint64(addr *uint64, val uint64) {
+	for {
+		o := atomic.LoadUint64(addr)
+		n := o | val
+		if atomic.CompareAndSwapUint64(addr, o, n) {
+			break
+		}
+	}
+}
+
+func XorUint64(addr *uint64, val uint64) {
+	for {
+		o := atomic.LoadUint64(addr)
+		n := o ^ val
+		if atomic.CompareAndSwapUint64(addr, o, n) {
+			break
+		}
+	}
+}
+
+func CompareAndSwapUint64(addr *uint64, old, new uint64) (prev uint64) {
+	for {
+		prev = atomic.LoadUint64(addr)
+		if prev != old {
+			return
+		}
+		if atomic.CompareAndSwapUint64(addr, old, new) {
+			return
+		}
+	}
+}