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py/pystack: Use "pystack exhausted" as error msg for out of pystack mem.
Using the message "maximum recursion depth exceeded" for when the pystack runs out of memory can be misleading because the pystack can run out for reasons other than deep recursion (although in most cases pystack exhaustion is probably indirectly related to deep recursion). And it's important to give the user more precise feedback as to the reason for the error: if they know precisely that the pystack was exhausted then they have a chance to increase the amount of memory available to the pystack (as opposed to not knowing if it was the C stack or pystack that ran out). Also, C stack exhaustion is more serious than pystack exhaustion because it could have been that the C stack overflowed and overwrote/corrupted some data and so the system must be restarted. The pystack can never corrupt data in this way so pystack exhaustion does not require a system restart. Knowing the difference between these two cases is therefore important. The actual exception type for pystack exhaustion remains as RuntimeError so that programatically it behaves the same as a C stack exhaustion.
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Lines changed: 6 additions & 1 deletion

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‎py/pystack.c‎

Lines changed: 2 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -43,7 +43,8 @@ void *mp_pystack_alloc(size_t n_bytes) {
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#endif
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if (MP_STATE_THREAD(pystack_cur) + n_bytes > MP_STATE_THREAD(pystack_end)) {
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// out of memory in the pystack
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mp_raise_recursion_depth();
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nlr_raise(mp_obj_new_exception_arg1(&mp_type_RuntimeError,
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MP_OBJ_NEW_QSTR(MP_QSTR_pystack_space_exhausted)));
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}
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void *ptr = MP_STATE_THREAD(pystack_cur);
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MP_STATE_THREAD(pystack_cur) += n_bytes;

‎py/qstrdefs.h‎

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Original file line numberDiff line numberDiff line change
@@ -52,3 +52,7 @@ Q(<genexpr>)
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Q(<string>)
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Q(<stdin>)
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Q(utf-8)
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#if MICROPY_ENABLE_PYSTACK
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Q(pystack exhausted)
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#endif

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