Use std::optional<LockedStream> to avoid exposing mutex

Author: JDevlieghere

lldb/include/lldb/Host/Editline.h

@@ -397,6 +397,9 @@ class Editline {
   FILE *m_input_file;
   lldb::LockableStreamFileSP m_output_stream_sp;
   lldb::LockableStreamFileSP m_error_stream_sp;
+
+  std::optional<LockedStreamFile> m_locked_output;
+
   ConnectionFileDescriptor m_input_connection;
 
   IsInputCompleteCallbackType m_is_input_complete_callback;

lldb/include/lldb/Host/StreamFile.h

@@ -60,13 +60,16 @@ class LockedStreamFile : public StreamFile {
 public:
   ~LockedStreamFile() { Flush(); }
 
+  LockedStreamFile(LockedStreamFile &&other)
+      : StreamFile(other.m_file_sp), m_lock(std::move(other.m_lock)) {}
+
 private:
   LockedStreamFile(std::shared_ptr<File> file, std::recursive_mutex &mutex)
-      : StreamFile(file), m_guard(mutex) {}
+      : StreamFile(file), m_lock(mutex) {}
 
   friend class LockableStreamFile;
 
-  std::lock_guard<std::recursive_mutex> m_guard;
+  std::unique_lock<std::recursive_mutex> m_lock;
 };
 
 class LockableStreamFile {
@@ -92,8 +95,6 @@ class LockableStreamFile {
   std::shared_ptr<File> GetUnlockedFileSP() { return m_file_sp; }
   /// @}
 
-  Mutex &GetMutex() { return m_mutex; }
-
 protected:
   std::shared_ptr<File> m_file_sp;
   Mutex &m_mutex;

lldb/source/Host/common/Editline.cpp

@@ -79,6 +79,19 @@ using namespace lldb_private::line_editor;
 
 #endif // #if LLDB_EDITLINE_USE_WCHAR
 
+template <typename T> class ScopedOptional {
+public:
+  template <typename... Args>
+  ScopedOptional(std::optional<T> &optional, Args &&...args)
+      : m_optional(optional) {
+    m_optional.emplace(std::forward<Args>(args)...);
+  }
+  ~ScopedOptional() { m_optional.reset(); }
+
+private:
+  std::optional<T> &m_optional;
+};
+
 bool IsOnlySpaces(const EditLineStringType &content) {
   for (wchar_t ch : content) {
     if (ch != EditLineCharType(' '))
@@ -541,9 +554,10 @@ int Editline::GetCharacter(EditLineGetCharType *c) {
   // Paint a ANSI formatted version of the desired prompt over the version
   // libedit draws. (will only be requested if colors are supported)
   if (m_needs_prompt_repaint) {
-    LockedStreamFile locked_stream = m_output_stream_sp->Lock();
+    ScopedOptional<LockedStreamFile> scope(m_locked_output,
+                                           m_output_stream_sp->Lock());
     MoveCursor(CursorLocation::EditingCursor, CursorLocation::EditingPrompt);
-    fprintf(locked_stream.GetFile().GetStream(),
+    fprintf(m_locked_output->GetFile().GetStream(),
             "%s"
             "%s"
             "%s",
@@ -581,10 +595,10 @@ int Editline::GetCharacter(EditLineGetCharType *c) {
     // indefinitely. This gives a chance for someone to interrupt us. After
     // Read returns, immediately lock the mutex again and check if we were
     // interrupted.
-    m_output_stream_sp->GetMutex().unlock();
+    m_locked_output.reset();
     int read_count =
         m_input_connection.Read(&ch, 1, std::nullopt, status, nullptr);
-    m_output_stream_sp->GetMutex().lock();
+    m_locked_output.emplace(m_output_stream_sp->Lock());
     if (m_editor_status == EditorStatus::Interrupted) {
       while (read_count > 0 && status == lldb::eConnectionStatusSuccess)
         read_count =
@@ -1599,7 +1613,8 @@ bool Editline::GetLine(std::string &line, bool &interrupted) {
   m_input_lines = std::vector<EditLineStringType>();
   m_input_lines.insert(m_input_lines.begin(), EditLineConstString(""));
 
-  LockedStreamFile locked_stream = m_output_stream_sp->Lock();
+  ScopedOptional<LockedStreamFile> scope(m_locked_output,
+                                         m_output_stream_sp->Lock());
 
   lldbassert(m_editor_status != EditorStatus::Editing);
   if (m_editor_status == EditorStatus::Interrupted) {
@@ -1619,7 +1634,7 @@ bool Editline::GetLine(std::string &line, bool &interrupted) {
   interrupted = m_editor_status == EditorStatus::Interrupted;
   if (!interrupted) {
     if (input == nullptr) {
-      fprintf(locked_stream.GetFile().GetStream(), "\n");
+      fprintf(m_locked_output->GetFile().GetStream(), "\n");
       m_editor_status = EditorStatus::EndOfInput;
     } else {
       m_history_sp->Enter(input);
@@ -1644,7 +1659,8 @@ bool Editline::GetLines(int first_line_number, StringList &lines,
   m_input_lines = std::vector<EditLineStringType>();
   m_input_lines.insert(m_input_lines.begin(), EditLineConstString(""));
 
-  LockedStreamFile locked_stream = m_output_stream_sp->Lock();
+  ScopedOptional<LockedStreamFile> scope(m_locked_output,
+                                         m_output_stream_sp->Lock());
 
   // Begin the line editing loop
   DisplayInput();