Move sync generics to their own packages

The presence of multiple packages in a single directory sometimes
confuses `go mod`, producing output like:
  go: downloading gvisor.dev/gvisor v0.0.0-20210601174640-77dc0f5bc94d
  $GOMODCACHE/gvisor.dev/gvisor@v0.0.0-20210601174640-77dc0f5bc94d/pkg/linewriter/linewriter.go:21:2: found packages sync (aliases.go) and seqatomic (generic_atomicptr_unsafe.go) in $GOMODCACHE/gvisor.dev/gvisor@v0.0.0-20210601174640-77dc0f5bc94d/pkg/sync
  imports.go:67:2: found packages tcp (accept.go) and rcv (rcv_test.go) in $GOMODCACHE/gvisor.dev/gvisor@v0.0.0-20210601174640-77dc0f5bc94d/pkg/tcpip/transport/tcp

PiperOrigin-RevId: 376956213

1 files changed, 20 insertions, 0 deletions

diff --git a/pkg/sync/atomicptrmap/atomicptrmap.go b/pkg/sync/atomicptrmap/atomicptrmap.go
new file mode 100644
index 000000000..867821ce9
--- /dev/null
+++ b/pkg/sync/atomicptrmap/atomicptrmap.go
@@ -0,0 +1,20 @@
+// Copyright 2020 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.
+
+// Package atomicptrmap instantiates generic_atomicptrmap for testing.
+package atomicptrmap
+
+type testValue struct {
+	val int
+}