Isolate the faulthandler Module Between Interpreters

[ericsnowcurrently]

(See gh-100227.)

Currently the faulthandler module has some state in _PyRuntimeState, including objects, which is shared by all interpreters. Interpreters should be isolated from each other, for a variety of reasons (including the possibility of a per-interpreter GIL). Isolating the module will involve moving some of the state to PyInterpreterState (and, under per-interpreter GIL, guarding other state with a global lock).

---

Code Analysis:

(expand)

Signals

The module installs handlers for various signals.

(expand)

fatal:

• SIGBUS - bus error
• SIGILL - illegal instruction
• SIGFPE - floating point exception
• SIGABRT - abort
• SIGSEGV - segfault

"user":

• the 5 fatal signals
• others (up to Py_NSIG)

handlers:

• faulthandler_fatal_error(signum)
• faulthandler_exc_handler() (on Windows)
• faulthandler_user()

State

Fields

https://github.com/python/cpython/blob/main/Include/internal/pycore_faulthandler.h#L49-L86
https://github.com/python/cpython/blob/main/Include/internal/pycore_runtime.h#L146

raw

cpython/Include/internal/pycore_faulthandler.h

Lines 49 to 86 in 62251c3

	struct _faulthandler_runtime_state {
	struct {
	int enabled;
	PyObject *file;
	int fd;
	int all_threads;
	PyInterpreterState *interp;
	#ifdef MS_WINDOWS
	void *exc_handler;
	#endif
	} fatal_error;
	struct {
	PyObject *file;
	int fd;
	PY_TIMEOUT_T timeout_us; /* timeout in microseconds */
	int repeat;
	PyInterpreterState *interp;
	int exit;
	char *header;
	size_t header_len;
	/* The main thread always holds this lock. It is only released when
	faulthandler_thread() is interrupted before this thread exits, or at
	Python exit. */
	PyThread_type_lock cancel_event;
	/* released by child thread when joined */
	PyThread_type_lock running;
	} thread;
	#ifdef FAULTHANDLER_USER
	struct faulthandler_user_signal *user_signals;
	#endif
	#ifdef FAULTHANDLER_USE_ALT_STACK
	stack_t stack;
	stack_t old_stack;
	#endif
	};

cpython/Include/internal/pycore_faulthandler.h

Lines 36 to 46 in 62251c3

	#ifdef FAULTHANDLER_USER
	struct faulthandler_user_signal {
	int enabled;
	PyObject *file;
	int fd;
	int all_threads;
	int chain;
	_Py_sighandler_t previous;
	PyInterpreterState *interp;
	};
	#endif /* FAULTHANDLER_USER */

tables:

name	type	#ifdef	notes
fatal_error
. enabled	bool		"is faulthandler enabled?"
. file	PyObject *		only for keeping .fd alive
. fd	int
. all_threads	bool
. interp	PyInterpreterState *		show only its threads the one that enabled faulthandler
. exc_handler	void *	MS_WINDOWS
name	type	#ifdef	notes
thread	---
. file	PyObject *		only for keeping .fd alive
. fd	int		defaults to sys.stderr
. timeout_us	PY_TIMEOUT_T
. repeat	bool
. interp	PyInterpreterState *		show only its threads the one that requested the info
. exit	bool
. header	char *
. header_len	size_t
. cancel_event	PyThread_type_lock
. running	PyThread_type_lock
name	type	#ifdef	notes
user_signals	struct faulthandler_user_signal *	FAULTHANDLER_USER	a dynamically allocated array (Py_NSIG)
user_signals[signum]	---
. enabled	bool
. file	PyObject *
. fd	int
. all_threads	bool
. chain	bool
. previous	_Py_sighandler_t
. interp	PyInterpreterState *		show only its threads the one that added the handler
name	type	#ifdef	notes
old_stack	stack_t	FAULTHANDLER_USE_ALT_STACK
stack	stack_t	FAULTHANDLER_USE_ALT_STACK

Usage

simple:

name	context	get	set
fatal_error
. enabled	module	faulthandler_is_enabled()	faulthandler_disable_py()
	signal	faulthandler_fatal_error()
	internal	faulthandler_enable() faulthandler_disable()	faulthandler_enable() faulthandler_disable()
. file	module	faulthandler_traverse()	faulthandler_py_enable() faulthandler_traverse()
	internal	faulthandler_disable()	faulthandler_disable()
. fd		module
	signal	faulthandler_fatal_error() faulthandler_exc_handler()
. all_threads	module		faulthandler_py_enable()
	signal	faulthandler_fatal_error() faulthandler_exc_handler()
. interp	module		faulthandler_py_enable()
	internal	faulthandler_fatal_error() faulthandler_exc_handler()
. exc_handler	internal	faulthandler_enable() faulthandler_disable()	faulthandler_enable() faulthandler_disable()
name	context	get	set
thread
. file	module	faulthandler_dump_traceback_later() faulthandler_traverse()	faulthandler_dump_traceback_later() faulthandler_traverse()
	internal	cancel_dump_traceback_later()	cancel_dump_traceback_later()
. fd
module		faulthandler_dump_traceback_later()
	thread	faulthandler_thread()
. timeout_us	module		faulthandler_dump_traceback_later()
	thread	faulthandler_thread()
. repeat	module		faulthandler_dump_traceback_later()
	thread	faulthandler_thread()
. interp	module		faulthandler_dump_traceback_later()
	thread	faulthandler_thread()
. exit	module		faulthandler_dump_traceback_later()
	thread	faulthandler_thread()
. header	module		faulthandler_dump_traceback_later()
	thread	faulthandler_thread()
	internal	cancel_dump_traceback_later()	cancel_dump_traceback_later()
. header_len	module		faulthandler_dump_traceback_later()
	thread	faulthandler_thread()
. cancel_event	module	faulthandler_dump_traceback_later()	faulthandler_dump_traceback_later()
	thread	faulthandler_thread()
	internal	cancel_dump_traceback_later()
. running	module	faulthandler_dump_traceback_later()	faulthandler_dump_traceback_later()
	thread	faulthandler_thread()
	internal	cancel_dump_traceback_later()
name	context	get	set
user_signals	module	faulthandler_register_py() faulthandler_unregister_py()	faulthandler_register_py() faulthandler_traverse()
	C-API	_PyFaulthandler_Fini()	_PyFaulthandler_Fini()
	signal	faulthandler_user()
user_signals[signum]
. enabled	module	faulthandler_register_py()	faulthandler_register_py()
	signal	faulthandler_user()
	internal	faulthandler_unregister()	faulthandler_unregister()
. file	module	faulthandler_register_py() faulthandler_traverse()	faulthandler_register_py() faulthandler_traverse()
	internal	faulthandler_unregister()	faulthandler_unregister()
. fd	module		faulthandler_register_py()
	signal	faulthandler_user()
	internal		faulthandler_unregister()
. all_threads	module		faulthandler_register_py()
	signal	faulthandler_user()
. chain	module		faulthandler_register_py()
	signal	faulthandler_user()
. previous	module		faulthandler_register_py()
	signal	faulthandler_user()
	internal	faulthandler_unregister()
. interp	module		faulthandler_register_py()
	signal	faulthandler_user()
name	context	get	set
stack	C-API	_PyFaulthandler_Init() _PyFaulthandler_Fini()
	internal	faulthandler_enable() faulthandler_register() faulthandler_allocate_stack()
old_stack	C-API	_PyFaulthandler_Fini()

modify data in complex fields:

name	context	calls
fatal_error .fd	signal	faulthandler_fatal_error() -> faulthandler_dump_traceback() faulthandler_fatal_error() -> _Py_DumpExtensionModules() faulthandler_exc_handler() faulthandler_exc_handler() -> _Py_DumpHexadecimal() faulthandler_exc_handler() -> faulthandler_dump_traceback()
thread.fd	thread	faulthandler_thread() -> _Py_write_noraise() faulthandler_thread() -> _Py_DumpTracebackThreads()
thread .cancel_event	module	faulthandler_dump_traceback_later()
	C-API	_PyFaulthandler_Fini()
	thread	faulthandler_thread()
	internal	cancel_dump_traceback_later()
thread .running	module	faulthandler_dump_traceback_later()
	thread	faulthandler_thread()
	internal	cancel_dump_traceback_later()
user_signals[signum] .fd	signal	faulthandler_user() -> faulthandler_dump_traceback()
stack	C-API	_PyFaulthandler_Init() _PyFaulthandler_Fini()
	internal	faulthandler_allocate_stack()
old_stack	internal	faulthandler_allocate_stack() -> sigaltstack()

[ericsnowcurrently]

Relevant: https://discuss.python.org/t/pep-684-a-per-interpreter-gil/19583/34