Fix flaky TestCatFileBatch/QueryTerminated test (#37159) (#37178)

Backport #37159 by @silverwind

`TestCatFileBatch/QueryTerminated` relied on timing to distinguish
`os.ErrClosed` vs `io.EOF` error paths. Replace `time.Sleep`-based
synchronization with a channel-based hook on pipe close, making both
error paths fully deterministic regardless of CI runner speed.

Ref:
https://github.com/go-gitea/gitea/actions/runs/24193070536/job/70615366804

---
This PR was written with the help of Claude Opus 4.6

Co-authored-by: silverwind <me@silverwind.io>
Co-authored-by: Claude (Opus 4.6) <noreply@anthropic.com>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

modules/git/catfile_batch_reader.go

@@ -13,63 +13,45 @@ import (
 	"strconv"
 	"strings"
 	"sync/atomic"
-	"time"
 
 	"code.gitea.io/gitea/modules/git/gitcmd"
 	"code.gitea.io/gitea/modules/log"
+	"code.gitea.io/gitea/modules/util"
 )
 
-var catFileBatchDebugWaitClose atomic.Int64
-
 type catFileBatchCommunicator struct {
-	closeFunc   func(err error)
+	closeFunc   atomic.Pointer[func(err error)]
 	reqWriter   io.Writer
 	respReader  *bufio.Reader
 	debugGitCmd *gitcmd.Command
 }
 
-func (b *catFileBatchCommunicator) Close() {
+func (b *catFileBatchCommunicator) Close(err ...error) {
-	if b.closeFunc != nil {
+	if fn := b.closeFunc.Swap(nil); fn != nil {
-		b.closeFunc(nil)
+		(*fn)(util.OptionalArg(err))
-		b.closeFunc = nil
 	}
 }
 
-// newCatFileBatch opens git cat-file --batch in the provided repo and returns a stdin pipe, a stdout reader and cancel function
+// newCatFileBatch opens git cat-file --batch/--batch-check/--batch-command command and prepares the stdin/stdout pipes for communication.
-func newCatFileBatch(ctx context.Context, repoPath string, cmdCatFile *gitcmd.Command) (ret *catFileBatchCommunicator) {
+func newCatFileBatch(ctx context.Context, repoPath string, cmdCatFile *gitcmd.Command) *catFileBatchCommunicator {
 	ctx, ctxCancel := context.WithCancelCause(ctx)
-
-	// We often want to feed the commits in order into cat-file --batch, followed by their trees and subtrees as necessary.
 	stdinWriter, stdoutReader, stdPipeClose := cmdCatFile.MakeStdinStdoutPipe()
-	pipeClose := func() {
-		if delay := catFileBatchDebugWaitClose.Load(); delay > 0 {
-			time.Sleep(time.Duration(delay)) // for testing purpose only
-		}
-		stdPipeClose()
-	}
-	closeFunc := func(err error) {
-		ctxCancel(err)
-		pipeClose()
-	}
-	return newCatFileBatchWithCloseFunc(ctx, repoPath, cmdCatFile, stdinWriter, stdoutReader, closeFunc)
-}
-
-func newCatFileBatchWithCloseFunc(ctx context.Context, repoPath string, cmdCatFile *gitcmd.Command,
-	stdinWriter gitcmd.PipeWriter, stdoutReader gitcmd.PipeReader, closeFunc func(err error),
-) *catFileBatchCommunicator {
 	ret := &catFileBatchCommunicator{
 		debugGitCmd: cmdCatFile,
-		closeFunc:   closeFunc,
 		reqWriter:   stdinWriter,
 		respReader:  bufio.NewReaderSize(stdoutReader, 32*1024), // use a buffered reader for rich operations
 	}
+	ret.closeFunc.Store(new(func(err error) {
+		ctxCancel(err)
+		stdPipeClose()
+	}))
 
 	err := cmdCatFile.WithDir(repoPath).StartWithStderr(ctx)
 	if err != nil {
 		log.Error("Unable to start git command %v: %v", cmdCatFile.LogString(), err)
 		// ideally here it should return the error, but it would require refactoring all callers
 		// so just return a dummy communicator that does nothing, almost the same behavior as before, not bad
-		closeFunc(err)
+		ret.Close(err)
 		return ret
 	}
 
@@ -78,12 +60,33 @@ func newCatFileBatchWithCloseFunc(ctx context.Context, repoPath string, cmdCatFi
 		if err != nil && !errors.Is(err, context.Canceled) {
 			log.Error("cat-file --batch command failed in repo %s, error: %v", repoPath, err)
 		}
-		closeFunc(err)
+		ret.Close(err)
 	}()
 
 	return ret
 }
 
+func (b *catFileBatchCommunicator) debugKill() (ret struct {
+	beforeClose chan struct{}
+	blockClose  chan struct{}
+	afterClose  chan struct{}
+},
+) {
+	ret.beforeClose = make(chan struct{})
+	ret.blockClose = make(chan struct{})
+	ret.afterClose = make(chan struct{})
+	oldCloseFunc := b.closeFunc.Load()
+	b.closeFunc.Store(new(func(err error) {
+		b.closeFunc.Store(nil)
+		close(ret.beforeClose)
+		<-ret.blockClose
+		(*oldCloseFunc)(err)
+		close(ret.afterClose)
+	}))
+	b.debugGitCmd.DebugKill()
+	return ret
+}
+
 // catFileBatchParseInfoLine reads the header line from cat-file --batch
 // We expect: <oid> SP <type> SP <size> LF
 // then leaving the rest of the stream "<contents> LF" to be read

modules/git/catfile_batch_test.go

@@ -7,9 +7,7 @@ import (
 	"io"
 	"os"
 	"path/filepath"
-	"sync"
 	"testing"
-	"time"
 
 	"code.gitea.io/gitea/modules/test"
 
@@ -39,13 +37,22 @@ func testCatFileBatch(t *testing.T) {
 		require.Error(t, err)
 	})
 
-	simulateQueryTerminated := func(pipeCloseDelay, pipeReadDelay time.Duration) (errRead error) {
+	simulateQueryTerminated := func(t *testing.T, errBeforePipeClose, errAfterPipeClose error) {
-		catFileBatchDebugWaitClose.Store(int64(pipeCloseDelay))
+		readError := func(t *testing.T, r io.Reader, expectedErr error) {
-		defer catFileBatchDebugWaitClose.Store(0)
+			if expectedErr == nil {
+				return // expectedErr == nil means this read should be skipped
+			}
+			n, err := r.Read(make([]byte, 100))
+			assert.Zero(t, n)
+			assert.ErrorIs(t, err, expectedErr)
+		}
+
 		batch, err := NewBatch(t.Context(), filepath.Join(testReposDir, "repo1_bare"))
 		require.NoError(t, err)
 		defer batch.Close()
-		_, _ = batch.QueryInfo("e2129701f1a4d54dc44f03c93bca0a2aec7c5449")
+		_, err = batch.QueryInfo("e2129701f1a4d54dc44f03c93bca0a2aec7c5449")
+		require.NoError(t, err)
+
 		var c *catFileBatchCommunicator
 		switch b := batch.(type) {
 		case *catFileBatchLegacy:
@@ -58,24 +65,18 @@ func testCatFileBatch(t *testing.T) {
 			t.FailNow()
 		}
 
-		wg := sync.WaitGroup{}
+		require.NotEqual(t, errBeforePipeClose == nil, errAfterPipeClose == nil, "must set exactly one of the expected errors")
-		wg.Go(func() {
-			time.Sleep(pipeReadDelay)
-			var n int
-			n, errRead = c.respReader.Read(make([]byte, 100))
-			assert.Zero(t, n)
-		})
-		time.Sleep(10 * time.Millisecond)
-		c.debugGitCmd.DebugKill()
-		wg.Wait()
-		return errRead
-	}
 
+		inceptor := c.debugKill()
+		<-inceptor.beforeClose                         // wait for the command's Close to be called, the pipe is not closed yet
+		readError(t, c.respReader, errBeforePipeClose) // then caller will read on an open pipe which will be closed soon
+		close(inceptor.blockClose)                     // continue to close the pipe
+		<-inceptor.afterClose                          // wait for the pipe to be closed
+		readError(t, c.respReader, errAfterPipeClose)  // then caller will read on a closed pipe
+	}
 	t.Run("QueryTerminated", func(t *testing.T) {
-		err := simulateQueryTerminated(0, 20*time.Millisecond)
+		simulateQueryTerminated(t, io.EOF, nil)       // reader is faster
-		assert.ErrorIs(t, err, os.ErrClosed) // pipes are closed faster
+		simulateQueryTerminated(t, nil, os.ErrClosed) // pipes are closed faster
-		err = simulateQueryTerminated(40*time.Millisecond, 20*time.Millisecond)
-		assert.ErrorIs(t, err, io.EOF) // reader is faster
 	})
 
 	batch, err := NewBatch(t.Context(), filepath.Join(testReposDir, "repo1_bare"))