cmd/go/internal/lockedfile: add a unit-test for Transform

Updates #35425

Change-Id: I9ca2251246ee2fa9bb7a335d5eff94d3c9f1f004
Reviewed-on: https://go-review.googlesource.com/c/go/+/206143
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

diff --git a/src/cmd/go/internal/lockedfile/transform_test.go b/src/cmd/go/internal/lockedfile/transform_test.go
new file mode 100644 (file)
index 0000000..407d48e
--- /dev/null
+++ b/src/cmd/go/internal/lockedfile/transform_test.go
@@ -0,0 +1,104 @@
+// Copyright 2019 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// js does not support inter-process file locking.
+// +build !js
+
+package lockedfile_test
+
+import (
+       "bytes"
+       "encoding/binary"
+       "math/rand"
+       "path/filepath"
+       "testing"
+       "time"
+
+       "cmd/go/internal/lockedfile"
+)
+
+func isPowerOf2(x int) bool {
+       return x > 0 && x&(x-1) == 0
+}
+
+func roundDownToPowerOf2(x int) int {
+       if x <= 0 {
+               panic("nonpositive x")
+       }
+       bit := 1
+       for x != bit {
+               x = x &^ bit
+               bit <<= 1
+       }
+       return x
+}
+
+func TestTransform(t *testing.T) {
+       dir, remove := mustTempDir(t)
+       defer remove()
+       path := filepath.Join(dir, "blob.bin")
+
+       const maxChunkWords = 8 << 10
+       buf := make([]byte, 2*maxChunkWords*8)
+       for i := uint64(0); i < 2*maxChunkWords; i++ {
+               binary.LittleEndian.PutUint64(buf[i*8:], i)
+       }
+       if err := lockedfile.Write(path, bytes.NewReader(buf[:8]), 0666); err != nil {
+               t.Fatal(err)
+       }
+
+       var attempts int64 = 128
+       if !testing.Short() {
+               attempts *= 16
+       }
+       const parallel = 32
+
+       var sem = make(chan bool, parallel)
+
+       for n := attempts; n > 0; n-- {
+               sem <- true
+               go func() {
+                       defer func() { <-sem }()
+
+                       time.Sleep(time.Duration(rand.Intn(100)) * time.Microsecond)
+                       chunkWords := roundDownToPowerOf2(rand.Intn(maxChunkWords) + 1)
+                       offset := rand.Intn(chunkWords)
+
+                       err := lockedfile.Transform(path, func(data []byte) (chunk []byte, err error) {
+                               chunk = buf[offset*8 : (offset+chunkWords)*8]
+
+                               if len(data)&^7 != len(data) {
+                                       t.Errorf("read %d bytes, but each write is an integer multiple of 8 bytes", len(data))
+                                       return chunk, nil
+                               }
+
+                               words := len(data) / 8
+                               if !isPowerOf2(words) {
+                                       t.Errorf("read %d 8-byte words, but each write is a power-of-2 number of words", words)
+                                       return chunk, nil
+                               }
+
+                               u := binary.LittleEndian.Uint64(data)
+                               for i := 1; i < words; i++ {
+                                       next := binary.LittleEndian.Uint64(data[i*8:])
+                                       if next != u+1 {
+                                               t.Errorf("wrote sequential integers, but read integer out of sequence at offset %d", i)
+                                               return chunk, nil
+                                       }
+                                       u = next
+                               }
+
+                               return chunk, nil
+                       })
+
+                       if err != nil {
+                               t.Errorf("unexpected error from Transform: %v", err)
+                       }
+               }()
+       }
+
+       for n := parallel; n > 0; n-- {
+               sem <- true
+       }
+}