Add //pkg/sync:generic_atomicptr.

PiperOrigin-RevId: 215620949
Change-Id: I519da4b44386d950443e5784fb8c48ff9a36c5d3

pkg/sync/BUILD

@@ -7,6 +7,14 @@ package(
 
 load("//tools/go_generics:defs.bzl", "go_template")
 
+go_template(
+    name = "generic_atomicptr",
+    srcs = ["atomicptr_unsafe.go"],
+    types = [
+        "Value",
+    ],
+)
+
 go_template(
     name = "generic_seqatomic",
     srcs = ["seqatomic_unsafe.go"],

pkg/sync/atomicptr_unsafe.go

@@ -0,0 +1,46 @@
+// Copyright 2018 Google Inc.
+//
+// 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.
+
+// 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 (
+	"sync/atomic"
+	"unsafe"
+)
+
+// Value is a required type parameter.
+type Value struct{}
+
+// An AtomicPtr is a pointer to a value of type Value that can be atomically
+// loaded and stored. The zero value of an AtomicPtr represents nil.
+//
+// Note that copying AtomicPtr by value performs a non-atomic read of the
+// stored pointer, which is unsafe if Store() can be called concurrently; in
+// this case, do `dst.Store(src.Load())` instead.
+type AtomicPtr struct {
+	ptr unsafe.Pointer
+}
+
+// Load returns the value set by the most recent Store. It returns nil if there
+// has been no previous call to Store.
+func (p *AtomicPtr) Load() *Value {
+	return (*Value)(atomic.LoadPointer(&p.ptr))
+}
+
+// Store sets the value returned by Load to x.
+func (p *AtomicPtr) Store(x *Value) {
+	atomic.StorePointer(&p.ptr, (unsafe.Pointer)(x))
+}

pkg/sync/atomicptrtest/BUILD

@@ -0,0 +1,28 @@
+package(licenses = ["notice"])  # Apache 2.0
+
+load("//tools/go_stateify:defs.bzl", "go_library", "go_test")
+load("//tools/go_generics:defs.bzl", "go_template_instance")
+
+go_template_instance(
+    name = "atomicptr_int",
+    out = "atomicptr_int.go",
+    package = "atomicptr",
+    suffix = "Int",
+    template = "//pkg/sync:generic_atomicptr",
+    types = {
+        "Value": "int",
+    },
+)
+
+go_library(
+    name = "atomicptr",
+    srcs = ["atomicptr_int.go"],
+    importpath = "gvisor.googlesource.com/gvisor/pkg/sync/atomicptr",
+)
+
+go_test(
+    name = "atomicptr_test",
+    size = "small",
+    srcs = ["atomicptr_test.go"],
+    embed = [":atomicptr"],
+)

pkg/sync/atomicptrtest/atomicptr_test.go

@@ -0,0 +1,40 @@
+// Copyright 2018 Google Inc.
+//
+// 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.
+
+package atomicptr
+
+import (
+	"testing"
+)
+
+func newInt(val int) *int {
+	return &val
+}
+
+func TestAtomicPtr(t *testing.T) {
+	var p AtomicPtrInt
+	if got := p.Load(); got != nil {
+		t.Errorf("initial value is %p (%v), wanted nil", got, got)
+	}
+	want := newInt(42)
+	p.Store(want)
+	if got := p.Load(); got != want {
+		t.Errorf("wrong value: got %p (%v), wanted %p (%v)", got, got, want, want)
+	}
+	want = newInt(100)
+	p.Store(want)
+	if got := p.Load(); got != want {
+		t.Errorf("wrong value: got %p (%v), wanted %p (%v)", got, got, want, want)
+	}
+}