Strace-like functionality

[ionelmc]

Ruby has an very interesting tracer tool: https://github.com/tmm1/rbtrace/

Hunter could have something like that:

• IPC with SysV queues (tracer would write to the queue, and external process can read from it).
  • Now there's the question of POSIX queues. Or not. They aren't supported on OSX: http://semanchuk.com/philip/posix_ipc/#platforms
• Need external activation of tracer. There are two ways to do it:
  • On demand activation:
  • Tracer is installed from signal handler.
  • Signal handler is installed from pth file.
  • Only works for mainthread. Installing tracers in other threads means patching some PyThreadState structs from C code (dangerous, eg: https://github.com/bobfrank/pydebug/blob/master/debug.py#L291)
  • Passive tracer:
  • Tracer is always installed from pth file but I doesn't do anything until someone connects to queue.
  • Need to detects connections to queue. Or use signal to start pushing stuff in queue?
  • Overhead should be ok for CPython, but what about PyPy?
  • It would allow tracing threads too (since tracer can be installed for threads too).

[ionelmc]

If we'd use a signal I'd go with SIGTRAP: https://www.gnu.org/software/coreutils/manual/html_node/Signal-specifications.html (as opposed to rbtrace's SIGURG, also: https://github.com/tmm1/rbtrace/issues/53).

[ionelmc]

Take note of https://github.com/khamidou/lptrace

[ionelmc]

Make note of https://gist.github.com/CAFxX/571a1558db9a7b393579 and https://news.ycombinator.com/item?id=10195297 (a file-based queue technique).

[ionelmc]

For queues this seems like the package: http://semanchuk.com/philip/sysv_ipc/ (supports osx too).