Hi Pavel, Jonas,
I was trying to reduce a bug through c-reduce, so I decided to write a SBAPI script to make it easier.
I did find out, that after the first iteration, the reduction gets stuck forever.
I sampled the process and I saw the following (trimmed for readability).
Call graph:
[…]
8455 lldb_private::CommandInterpreter::GetScriptInterpreter(bool) (in _lldb.so) + 84 [0x111aff826]
8455 lldb_private::PluginManager::GetScriptInterpreterForLanguage(lldb::ScriptLanguage, lldb_private::CommandInterpreter&) (in _lldb.so) + 99 [0x111a1efcf]
8455 lldb_private::ScriptInterpreterPython::CreateInstance(lldb_private::CommandInterpreter&) (in _lldb.so) + 26 [0x111d128f4]
8455 std::__1::shared_ptr<lldb_private::ScriptInterpreterPython> std::__1::shared_ptr<lldb_private::ScriptInterpreterPython>::make_shared<lldb_private::CommandInterpreter&>(lldb_private::CommandInterpreter&&&) (in _lldb.so) + 72 [0x111d1b976]
8455 lldb_private::ScriptInterpreterPython::ScriptInterpreterPython(lldb_private::CommandInterpreter&) (in _lldb.so) + 353 [0x111d11ff3]
8455 lldb_private::ScriptInterpreterPython::InitializePrivate() (in _lldb.so) + 494 [0x111d12594]
8455 (anonymous namespace)::InitializePythonRAII::~InitializePythonRAII() (in _lldb.so) + 146 [0x111d1b446]
8455 lldb_private::TerminalState::Restore() const (in _lldb.so) + 74 [0x111ac8268]
8455 tcsetattr (in libsystem_c.dylib) + 110 [0x7fff7b95b585]
8455 ioctl (in libsystem_kernel.dylib) + 151 [0x7fff7ba19b44]
8455 __ioctl (in libsystem_kernel.dylib) + 10 [0x7fff7ba19b5a]
It looks like lldb gets stuck forever in tcsetattr(), and there are no other threads waiting so it’s not entirely obvious to me why it’s waiting there.
I was never able to reproduce this with an interactive session, I suspect this is somehow related to the fact that c-reduce spawns a thread in the background, hence it doesn’t have a TTY associated.
I looked at the code that does this, and I wasn’t really able to find a reason why we need to do this work. Jim thinks it might have been needed historically.
git blame doesn’t really help that much either. If I remove the code, everything still passes and it’s functional, but before moving forward with this I would like to collect your opinions.
$ git diff
diff --git a/lldb/source/Plugins/ScriptInterpreter/Python/ScriptInterpreterPython.cpp b/lldb/source/Plugins/ScriptInterpreter/Python/ScriptInterpreterPython.cpp
index ee94a183e0d…c53b3bd0fb6 100644
— a/lldb/source/Plugins/ScriptInterpreter/Python/ScriptInterpreterPython.cpp
+++ b/lldb/source/Plugins/ScriptInterpreter/Python/ScriptInterpreterPython.cpp
@@ -224,10 +224,6 @@ struct InitializePythonRAII {
public:
InitializePythonRAII()
: m_gil_state(PyGILState_UNLOCKED), m_was_already_initialized(false) {
- // Python will muck with STDIN terminal state, so save off any current TTY
- // settings so we can restore them.
- m_stdin_tty_state.Save(STDIN_FILENO, false);