Data race

[mholt]

These statistic variables at the package scope are not atomic:

go-xmp/xmp/node.go

Line 27 in bbfd8f1

npAllocs, npFrees, npHits, npReturns int64

So I'm getting data races when processing multiple separate files concurrently, each in their own goroutine:

WARNING: DATA RACE
Read at 0x000008332ea0 by goroutine 1243:
  github.com/trimmer-io/go-xmp/xmp.NewNode()
      /home/matt/go/pkg/mod/github.com/trimmer-io/go-xmp@v1.0.0/xmp/node.go:83 +0xcb
  github.com/trimmer-io/go-xmp/xmp.copyNode()
      /home/matt/go/pkg/mod/github.com/trimmer-io/go-xmp@v1.0.0/xmp/node.go:121 +0xa8
  github.com/trimmer-io/go-xmp/xmp.copyNodes()
      /home/matt/go/pkg/mod/github.com/trimmer-io/go-xmp@v1.0.0/xmp/node.go:133 +0x169
  github.com/trimmer-io/go-xmp/xmp.copyNode()
      /home/matt/go/pkg/mod/github.com/trimmer-io/go-xmp@v1.0.0/xmp/node.go:126 +0x42c
  github.com/trimmer-io/go-xmp/xmp.(*Decoder).decodeNode()
      /home/matt/go/pkg/mod/github.com/trimmer-io/go-xmp@v1.0.0/xmp/unmarshal.go:175 +0x693
  github.com/trimmer-io/go-xmp/xmp.(*Decoder).Decode()
      /home/matt/go/pkg/mod/github.com/trimmer-io/go-xmp@v1.0.0/xmp/unmarshal.go:133 +0x1a84
  github.com/trimmer-io/go-xmp/xmp.Unmarshal()
      /home/matt/go/pkg/mod/github.com/trimmer-io/go-xmp@v1.0.0/xmp/unmarshal.go:60 +0xce
...

Previous write at 0x000008332ea0 by goroutine 2555:
  github.com/trimmer-io/go-xmp/xmp.NewNode()
      /home/matt/go/pkg/mod/github.com/trimmer-io/go-xmp@v1.0.0/xmp/node.go:83 +0xe8
  github.com/trimmer-io/go-xmp/xmp.(*Node).UnmarshalXML()
      /home/matt/go/pkg/mod/github.com/trimmer-io/go-xmp@v1.0.0/xmp/node.go:379 +0x3f4
  github.com/trimmer-io/go-xmp/xmp.(*Node).UnmarshalXML()
      /home/matt/go/pkg/mod/github.com/trimmer-io/go-xmp@v1.0.0/xmp/node.go:380 +0x4a9
  encoding/xml.(*Decoder).unmarshalInterface()
      /usr/local/go/src/encoding/xml/read.go:211 +0x1ac
  encoding/xml.(*Decoder).unmarshal()
      /usr/local/go/src/encoding/xml/read.go:363 +0xc6d
  encoding/xml.(*Decoder).DecodeElement()
      /usr/local/go/src/encoding/xml/read.go:156 +0x2a4
  encoding/xml.(*Decoder).Decode()
      /usr/local/go/src/encoding/xml/read.go:140 +0x84
  github.com/trimmer-io/go-xmp/xmp.(*Decoder).Decode()
      /home/matt/go/pkg/mod/github.com/trimmer-io/go-xmp@v1.0.0/xmp/unmarshal.go:81 +0x204
  github.com/trimmer-io/go-xmp/xmp.Unmarshal()
      /home/matt/go/pkg/mod/github.com/trimmer-io/go-xmp@v1.0.0/xmp/unmarshal.go:60 +0xce

Fortunately, these are int64, so the easy solution is to use the atomic package, for example to add 1 to a variable, you simply do atomic.AddInt64(&npAllocs, 1).