Isolate the faulthandler Module Between Interpreters

(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()`

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Isolate the faulthandler Module Between Interpreters #101509

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	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
	};

	#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 */

Uh oh!

Isolate the faulthandler Module Between Interpreters #101509

Description

Signals

State

Fields

Usage

Metadata

Metadata

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Development

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