Add PyUnstable_DumpTraceback() and PyUnstable_DumpTracebackThreads()

[vstinner]

Hi,

@alexmalyshev proposes adding PyUnstable_DumpTraceback() and PyUnstable_DumpTracebackThreads() functions to dump the Python traceback to a file descriptor:

const char* PyUnstable_DumpTraceback(int fd, PyThreadState *tstate);
const char* PyUnstable_DumpTracebackThreads(int fd, PyInterpreterState *interp, PyThreadState *current_tstate);

These functions are safe to use from signal handlers. The caller does not need to hold an attached thread state.

If PyUnstable_DumpTraceback() or PyUnstable_DumpTracebackThreads() cannot dump the traceback, it returns an error message. The caller is free to ignore it, or to report it someho to the user. It cannot raise an exception since it can be called without an attached thread state.

See the issue and the pull request. See the pull request for the whole API.

UPDATE: Change PyUnstable_DumpTraceback() return type from void to const char*.

Vote to add these 2 functions:

• @encukou
• @erlend-aasland
• @serhiy-storchaka
• @vstinner
• @zooba

[encukou]

This sounds good in general.

I think PyUnstable_DumpTraceback should use the same error reporting mechanism, even if it always succeeds today.

If we're already displaying human-readable debug output, maybe PyUnstable_DumpTracebackThreads should also (attempt to) print any error message to fd? That shouldn't break anything and could simplify the debugging.

[vstinner]

I think PyUnstable_DumpTraceback should use the same error reporting mechanism, even if it always succeeds today.

Good idea. I changed the API to return const char*.

If we're already displaying human-readable debug output, maybe PyUnstable_DumpTracebackThreads should also (attempt to) print any error message to fd? That shouldn't break anything and could simplify the debugging.

Yes, PyUnstable_DumpTracebackThreads() can be modified to write the error to fd.

[vstinner]

Ping @erlend-aasland @serhiy-storchaka.

[encukou]

Ping @serhiy-storchaka.