chore: avoid trying to stream data

`profile.Parse` always call `io.ReadAll` so avoid the trouble and a
goroutine and do it ourselves.

Add some limited testing (testing the parsed stack is volatile and not
really feasible).

2 files changed, 100 insertions, 8 deletions

diff --git a/modules/process/manager_stacktraces.go b/modules/process/manager_stacktraces.go
index e260893113..a603e6a9f2 100644
--- a/modules/process/manager_stacktraces.go
+++ b/modules/process/manager_stacktraces.go
@@ -4,8 +4,8 @@
 package process
 
 import (
+	"bytes"
 	"fmt"
-	"io"
 	"runtime/pprof"
 	"sort"
 	"time"
@@ -175,13 +175,12 @@ func (pm *Manager) ProcessStacktraces(flat, noSystem bool) ([]*Process, int, int
 	// Now from within the lock we need to get the goroutines.
 	// Why? If we release the lock then between between filling the above map and getting
 	// the stacktraces another process could be created which would then look like a dead process below
-	reader, writer := io.Pipe()
-	defer reader.Close()
-	go func() {
-		err := pprof.Lookup("goroutine").WriteTo(writer, 0)
-		_ = writer.CloseWithError(err)
-	}()
-	stacks, err = profile.Parse(reader)
+	var buf bytes.Buffer
+	if err := pprof.Lookup("goroutine").WriteTo(&buf, 0); err != nil {
+		return nil, 0, 0, err
+	}
+
+	stacks, err = profile.ParseData(buf.Bytes())
 	if err != nil {
 		return nil, 0, 0, err
 	}
diff --git a/modules/process/manager_stacktraces_test.go b/modules/process/manager_stacktraces_test.go
new file mode 100644
index 0000000000..d00fbc5ec8
--- /dev/null
+++ b/modules/process/manager_stacktraces_test.go
@@ -0,0 +1,93 @@
+// Copyright 2025 The Forgejo Authors. All rights reserved.
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+package process
+
+import (
+	"context"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestProcessStacktraces(t *testing.T) {
+	_, _, finish := GetManager().AddContext(context.Background(), "Normal process")
+	defer finish()
+	parentCtx, _, finish := GetManager().AddContext(context.Background(), "Children normal process")
+	defer finish()
+	_, _, finish = GetManager().AddContext(parentCtx, "Children process")
+	defer finish()
+	_, _, finish = GetManager().AddTypedContext(context.Background(), "System process", SystemProcessType, true)
+	defer finish()
+
+	t.Run("No flat with no system process", func(t *testing.T) {
+		processes, processCount, _, err := GetManager().ProcessStacktraces(false, true)
+		require.NoError(t, err)
+		assert.EqualValues(t, 4, processCount)
+		assert.Len(t, processes, 2)
+
+		assert.EqualValues(t, "Children normal process", processes[0].Description)
+		assert.EqualValues(t, NormalProcessType, processes[0].Type)
+		assert.Empty(t, processes[0].ParentPID)
+		assert.Len(t, processes[0].Children, 1)
+
+		assert.EqualValues(t, "Children process", processes[0].Children[0].Description)
+		assert.EqualValues(t, processes[0].PID, processes[0].Children[0].ParentPID)
+
+		assert.EqualValues(t, "Normal process", processes[1].Description)
+		assert.EqualValues(t, NormalProcessType, processes[1].Type)
+		assert.Empty(t, processes[1].ParentPID)
+		assert.Empty(t, processes[1].Children)
+	})
+
+	t.Run("Flat with no system process", func(t *testing.T) {
+		processes, processCount, _, err := GetManager().ProcessStacktraces(true, true)
+		require.NoError(t, err)
+		assert.EqualValues(t, 4, processCount)
+		assert.Len(t, processes, 3)
+
+		assert.EqualValues(t, "Children process", processes[0].Description)
+		assert.EqualValues(t, NormalProcessType, processes[0].Type)
+		assert.EqualValues(t, processes[1].PID, processes[0].ParentPID)
+		assert.Empty(t, processes[0].Children)
+
+		assert.EqualValues(t, "Children normal process", processes[1].Description)
+		assert.EqualValues(t, NormalProcessType, processes[1].Type)
+		assert.Empty(t, processes[1].ParentPID)
+		assert.Empty(t, processes[1].Children)
+
+		assert.EqualValues(t, "Normal process", processes[2].Description)
+		assert.EqualValues(t, NormalProcessType, processes[2].Type)
+		assert.Empty(t, processes[2].ParentPID)
+		assert.Empty(t, processes[2].Children)
+	})
+
+	t.Run("System process", func(t *testing.T) {
+		processes, processCount, _, err := GetManager().ProcessStacktraces(false, false)
+		require.NoError(t, err)
+		assert.EqualValues(t, 4, processCount)
+		assert.Len(t, processes, 4)
+
+		assert.EqualValues(t, "System process", processes[0].Description)
+		assert.EqualValues(t, SystemProcessType, processes[0].Type)
+		assert.Empty(t, processes[0].ParentPID)
+		assert.Empty(t, processes[0].Children)
+
+		assert.EqualValues(t, "Children normal process", processes[1].Description)
+		assert.EqualValues(t, NormalProcessType, processes[1].Type)
+		assert.Empty(t, processes[1].ParentPID)
+		assert.Len(t, processes[1].Children, 1)
+
+		assert.EqualValues(t, "Normal process", processes[2].Description)
+		assert.EqualValues(t, NormalProcessType, processes[2].Type)
+		assert.Empty(t, processes[2].ParentPID)
+		assert.Empty(t, processes[2].Children)
+
+		// This is the "main" pid, testing code always runs in a goroutine.
+		assert.EqualValues(t, "(unassociated)", processes[3].Description)
+		assert.EqualValues(t, NoneProcessType, processes[3].Type)
+		assert.Empty(t, processes[3].ParentPID)
+		assert.Empty(t, processes[3].Children)
+	})
+}