provider/template: fix race causing panic in template_file

The render code path in `template_file` was doing unsynchronized access
to a shared mapping of functions in `config.Func`.

This caused a race condition that was most often triggered when a
`template_file` had a `count` of more than one, and expressed itself as
a panic in the plugin followed by a cascade of "unexpected EOF" errors
through the plugin system.

Here, we simply turn the FuncMap from shared state into a generated
value, which avoids the race. We do more re-initialization of the data
structure, but the performance implications are minimal, and we can
always revisit with a perf pass later now that the race is fixed.

builtin/providers/template/resource_template_file.go

@@ -155,7 +155,7 @@ func execute(s string, vars map[string]interface{}) (string, error) {
  cfg := lang.EvalConfig{
  GlobalScope: &ast.BasicScope{
  VarMap: varmap,
- FuncMap: config.Funcs,
+ FuncMap: config.Funcs(),
  },
  }
 

builtin/providers/template/resource_template_file_test.go

@@ -2,6 +2,7 @@ package template
 
 import (
  "fmt"
+ "sync"
  "testing"
 
  r "github.com/hashicorp/terraform/helper/resource"
@@ -76,6 +77,29 @@ func TestTemplateVariableChange(t *testing.T) {
  })
 }
 
+// This test covers a panic due to config.Func formerly being a
+// shared map, causing multiple template_file resources to try and
+// accessing it parallel during their lang.Eval() runs.
+//
+// Before fix, test fails under `go test -race`
+func TestTemplateSharedMemoryRace(t *testing.T) {
+ var wg sync.WaitGroup
+ for i := 0; i < 100; i++ {
+ go func(wg sync.WaitGroup, t *testing.T, i int) {
+ wg.Add(1)
+ out, err := execute("don't panic!", map[string]interface{}{})
+ if err != nil {
+ t.Fatalf("err: %s", err)
+ }
+ if out != "don't panic!" {
+ t.Fatalf("bad output: %s", out)
+ }
+ wg.Done()
+ }(wg, t, i)
+ }
+ wg.Wait()
+}
+
 func testTemplateConfig(template, vars string) string {
  return fmt.Sprintf(`
  resource "template_file" "t0" {

config/interpolate_funcs.go

@@ -20,10 +20,8 @@ import (
 )
 
 // Funcs is the mapping of built-in functions for configuration.
-var Funcs map[string]ast.Function
-
-func init() {
- Funcs = map[string]ast.Function{
+func Funcs() map[string]ast.Function {
+ return map[string]ast.Function{
  "cidrhost": interpolationFuncCidrHost(),
  "cidrnetmask": interpolationFuncCidrNetmask(),
  "cidrsubnet": interpolationFuncCidrSubnet(),

config/raw_config.go

@@ -300,7 +300,7 @@ type gobRawConfig struct {
 // langEvalConfig returns the evaluation configuration we use to execute.
 func langEvalConfig(vs map[string]ast.Variable) *lang.EvalConfig {
  funcMap := make(map[string]ast.Function)
- for k, v := range Funcs {
+ for k, v := range Funcs() {
  funcMap[k] = v
  }
  funcMap["lookup"] = interpolationFuncLookup(vs)