internal/counter: fix flaky test

Quim Montel points out that several raw calls to munmap had incomplete
effect and should be replaced by mappedFile.close().

The tests ran 15000 times without any failures.

Fixes golang/go#65182 (TestRotate flaky on Windows)
Fixes: golang/go#65255 (double panic caused by munmapping twice)

Change-Id: Ice445c4d5b521b4a49971eced07bcff1aadb157f
Reviewed-on: https://go-review.googlesource.com/c/telemetry/+/559498
Reviewed-by: Robert Findley <[email protected]>
Run-TryBot: Peter Weinberger <[email protected]>
Reviewed-by: Hyang-Ah Hana Kim <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>

Author: pjweinbgo

internal/counter/counter_test.go

@@ -26,7 +26,6 @@ import (
 	"testing"
 	"time"
 
-	"golang.org/x/telemetry/internal/mmap"
 	"golang.org/x/telemetry/internal/telemetry"
 	"golang.org/x/telemetry/internal/testenv"
 )
@@ -70,6 +69,7 @@ func TestBasic(t *testing.T) {
 }
 
 func TestMissingLocalDir(t *testing.T) {
+	testenv.SkipIfUnsupportedPlatform(t)
 	err := os.RemoveAll(telemetry.LocalDir)
 	if err != nil {
 		t.Fatal(err)
@@ -130,8 +130,7 @@ func close(f *file) {
 		// telemetry might have been off
 		return
 	}
-	mmap.Munmap(mf.mapping)
-	mf.f.Close()
+	mf.close()
 }
 
 func TestLarge(t *testing.T) {

internal/counter/file.go

@@ -8,7 +8,6 @@ import (
 	"bytes"
 	"errors"
 	"fmt"
-	"log"
 	"math/rand"
 	"os"
 	"path"
@@ -277,12 +276,8 @@ func (f *file) rotate1() (expire time.Time, cleanup func()) {
 			return
 		}
 		// now it is safe to clean up the old mapping
-		if err := previous.f.Close(); err != nil {
-			log.Print(err)
-		}
-		if err := munmap(previous.mapping); err != nil {
-			log.Print(err)
-		}
+		// Quim Montel pointed out the previous coeanup was incomplete
+		previous.close()
 	}
 
 	name, expire, err := f.filename(counterTime())
@@ -373,8 +368,7 @@ func Open() func() {
 			// telemetry might have been off
 			return
 		}
-		mmap.Munmap(mf.mapping)
-		mf.f.Close() // best effort
+		mf.close()
 	}
 }
 
@@ -406,6 +400,7 @@ func openMapped(name string, meta string, existing *mappedFile) (_ *mappedFile,
 		f:    f,
 		meta: meta,
 	}
+	// without this files cannot be cleanedup on Windows (affects tests)
 	runtime.SetFinalizer(m, (*mappedFile).close)
 	defer func() {
 		if err != nil {