Mechanism Loading Issues: nrn_dll_loaded does not update and Segfaults

[anilbey]

Context

Overview of the issue

When using NEURON for API development, we encountered an issue where nrn_dll_loaded remains empty even after mechanisms are loaded automatically. This discrepancy leads to a situation where the load_mechanisms function is unable to accurately determine if mechanisms have been loaded, resulting in a segmentation fault when attempting to load mechanisms that are already present. Additionally, the load_mechanisms function does not account for canonical vs. non-canonical path forms, causing further issues when paths provided are relative or symbolic links.

Expected result/behavior

The expected behavior is for nrn_dll_loaded to be accurately updated upon the automatic loading of mechanisms, allowing the load_mechanisms function to correctly identify already loaded mechanisms and prevent attempts to reload them, thus avoiding segmentation faults. Furthermore, the load_mechanisms function should convert provided paths to their canonical form before checking against already loaded paths to ensure reliability and prevent errors due to path discrepancies.

NEURON setup

• Version: 8.2.4 and 8.2.3 and possibly the older versions as well
• Installation method: pip
• OS + Version: OS-agnostic
• Compiler + Version: Compiler-agnostic

Minimal working example - MWE

To reproduce the issue regarding nrn_dll_loaded being empty and segmentation fault on mechanism reload:

1. nrn_dll_loaded is empty although the mechanisms are loaded:

from neuron import h, load_mechanisms, nrn_dll_loaded
print(nrn_dll_loaded)  # Expected to show loaded mechanisms, but shows []

>>> dir (neuron.h)  # these are the loaded mechanisms
['APCount', 'AlphaSynapse', 'Avogadro_constant', 'BBSaveState', 'BnlDev_StochKv', 'BnlDev_StochKv3', 'CVode', 'Ca', 'CaDynamics_DC0', 'CaDynamics_E2', 'Ca_HVA', 'Ca_HVA2', 'Ca_LVAst', 'ChkProb_StochKv', 'ChkProb_StochKv3', 'DEG', 'Deck', 'DetAMPANMDA', 'DetGABAAB', 'E', 'E_AMPA_GluSynapse', 'E_NMDA_GluSynapse', 'Exp2Syn', 'ExpSyn', 'FARADAY', 'FInitializeHandler', 'File', 'GAMMA', 'GUIMath', 'Gap', 'GluSynapse', 'Glyph', 'Graph', 'HBox', 'IClamp', 'Ih', 'Im', 'Impedance', 'InhPoissonStim', 'IntFire1', 'IntFire2', 'IntFire4', 'KSChan', 'KSGate', 'KSState', 'KSTrans', 'KTF_cal', 'KTF_can', 'KTF_cat', 'K_Pst', 'K_Tst',

2. Segmentation fault occurs since it tries to load the same mechanisms twice:

load_mechanisms(".")
# Results in SEGFAULT
# NEURON: The user defined name already exists: Ca
#  near line 0
#  objref hoc_obj_[2]