[Lldb-commits] [PATCH] D48463: Prevent dead locking when calling PrintAsync

[Raphael Isemann via Phabricator via lldb-commits]

teemperor added a reviewer: labath.
teemperor added a subscriber: labath.
teemperor added a comment.

Adding Pavel because he wrote the PrintAsync code.

Also @labath: Can you tell me what variables/functionality the `m_output_mutex` in Editline.cpp is supposed to shield? I don't see any documentation for that.

The `m_output_mutex` name suggests its related to console output, but we actually take the lock also when reading *input*. Especially in `EditLine::GetLine` we take a guard on the lock but then somehow unlock the guarded mutex from inside  `Editline::GetCharacter` that we call afterwards (which completely breaks this patch):

  // This mutex is locked by our caller (GetLine). Unlock it while we read a
  // character (blocking operation), so we do not hold the mutex
  // 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_mutex.unlock();
  int read_count = m_input_connection.Read(&ch, 1, llvm::None, status, NULL);
  m_output_mutex.lock();
  if (m_editor_status == EditorStatus::Interrupted) {
    while (read_count > 0 && status == lldb::eConnectionStatusSuccess)
      read_count = m_input_connection.Read(&ch, 1, llvm::None, status, NULL);
    lldbassert(status == lldb::eConnectionStatusInterrupted);
    return 0;
  }


https://reviews.llvm.org/D48463