8000 py/nlr: Implement jump callbacks. · micropython/micropython@2757acf · GitHub
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py/nlr: Implement jump callbacks.
NLR buffers are usually quite large (use lots of C stack) and expensive to push and pop. Some of the time they are only needed to perform clean up if an exception happens, and then they re-raise the exception. This commit allows optimizing that scenario by introducing a linked-list of NLR callbacks that are called automatically when an exception is raised. They are essentially a light-weight NLR handler that can implement a "finally" block, i.e. clean-up when an exception is raised, or (by passing `true` to nlr_pop_jump_callback) when execution leaves the scope. Signed-off-by: Damien George <damien@micropython.org>
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‎py/mpstate.h

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@@ -271,6 +271,7 @@ typedef struct _mp_state_thread_t {
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mp_obj_dict_t *dict_globals;
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nlr_buf_t *nlr_top;
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nlr_jump_callback_node_t *nlr_jump_callback_top;
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// pending exception object (MP_OBJ_NULL if not pending)
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volatile mp_obj_t mp_pending_exception;

‎py/nlr.c

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@@ -3,7 +3,7 @@
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*
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* The MIT License (MIT)
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*
6-
* Copyright (c) 2013-2017 Damien P. George
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* Copyright (c) 2013-2023 Damien P. George
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*
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* Permission is hereby granted, free of charge, to any person obtaining a copy
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* of this software and associated documentation files (the "Software"), to deal
@@ -50,6 +50,36 @@ void nlr_pop(void) {
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*top = (*top)->prev;
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}
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void nlr_push_jump_callback(nlr_jump_callback_node_t *node, nlr_jump_callback_fun_t fun) {
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nlr_jump_callback_node_t **top = &MP_STATE_THREAD(nlr_jump_callback_top);
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node->prev = *top;
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node->fun = fun;
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*top = node;
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}
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void nlr_pop_jump_callback(bool run_callback) {
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nlr_jump_callback_node_t **top = &MP_STATE_THREAD(nlr_jump_callback_top);
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nlr_jump_callback_node_t *cur = *top;
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*top = (*top)->prev;
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if (run_callback) {
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cur->fun(cur);
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}
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}
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// This function pops and runs all callbacks that were registered after `nlr`
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// was pushed (via nlr_push). It assumes:
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// - a descending C stack,
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// - that all nlr_jump_callback_node_t's in the linked-list pointed to by
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// nlr_jump_callback_top are on the C stack
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// It works by popping each node in turn until the next node is NULL or above
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// the `nlr` pointer on the C stack (and so pushed before `nlr` was pushed).
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void nlr_call_jump_callbacks(nlr_buf_t *nlr) {
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nlr_jump_callback_node_t **top = &MP_STATE_THREAD(nlr_jump_callback_top);
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while (*top != NULL && (void *)*top < (void *)nlr) {
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nlr_pop_jump_callback(true);
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}
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}
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#if MICROPY_ENABLE_VM_ABORT
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NORETURN void nlr_jump_abort(void) {
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MP_STATE_THREAD(nlr_top) = MP_STATE_VM(nlr_abort);

‎py/nlr.h

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@@ -3,7 +3,7 @@
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*
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* The MIT License (MIT)
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*
6-
* Copyright (c) 2013, 2014 Damien P. George
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* Copyright (c) 2013-2023 Damien P. George
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*
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* Permission is hereby granted, free of charge, to any person obtaining a copy
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* of this software and associated documentation files (the "Software"), to deal
@@ -31,6 +31,7 @@
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#include <limits.h>
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#include <assert.h>
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#include <stdbool.h>
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#include "py/mpconfig.h"
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@@ -123,6 +124,15 @@ struct _nlr_buf_t {
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#endif
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};
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typedef void (*nlr_jump_callback_fun_t)(void *ctx);
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typedef struct _nlr_jump_callback_node_t nlr_jump_callback_node_t;
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struct _nlr_jump_callback_node_t {
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nlr_jump_callback_node_t *prev;
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nlr_jump_callback_fun_t fun;
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};
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// Helper macros to save/restore the pystack state
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#if MICROPY_ENABLE_PYSTACK
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#define MP_NLR_SAVE_PYSTACK(nlr_buf) (nlr_buf)->pystack = MP_STATE_THREAD(pystack_cur)
@@ -140,6 +150,7 @@ struct _nlr_buf_t {
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nlr_jump_fail(val); \
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} \
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top->ret_val = val; \
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nlr_call_jump_callbacks(top); \
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MP_NLR_RESTORE_PYSTACK(top); \
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*_top_ptr = top->prev; \
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@@ -187,4 +198,16 @@ NORETURN void nlr_jump_fail(void *val);
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#endif
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// Push a callback on to the linked-list of NLR jump callbacks. The `node` pointer must
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// be on the C stack. The `fun` callback will be executed if an NLR jump is taken which
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// unwinds the C stack through this `node`.
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void nlr_push_jump_callback(nlr_jump_callback_node_t *node, nlr_jump_callback_fun_t fun);
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// Pop a callback from the linked-list of NLR jump callbacks. The corresponding function
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// will be called if `run_callback` is true.
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void nlr_pop_jump_callback(bool run_callback);
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// Pop and call all NLR jump callbacks that were registered after `nlr` buffer was pushed.
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void nlr_call_jump_callbacks(nlr_buf_t *nlr);
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#endif // MICROPY_INCLUDED_PY_NLR_H

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