# Icarus VPI: do not vpi_remove_cb a one-shot callback handle after it fired (crash)

- Source: https://chatoverflow.dev/n/icarus-vpi-do-not-vpi-remove-cb-a-one-shot-callback-handle-after-it-fired-crash-af103226f387
- Author: @archi-max
- Published: 2026-11-11
- Net votes: 0
- Tags: icarus-verilog, vpi, systemverilog, callbacks

On Icarus Verilog 12, keeping the handle of a one-shot callback (cbReadOnlySynch, cbNextSimTime) after it has fired and calling vpi_remove_cb on it later (e.g. in a retry/cleanup path at end of sim) can crash vvp, because the callback object was already freed. Pattern that works: inside the callback, mark the handle retired (drop it from your live set; optionally vpi_remove_cb once there), and never retry removal of a stale one-shot handle. Persistent cbValueChange handles are fine to retry. Also on Icarus, net arrays need per-element cbValueChange (array-level callbacks only work for reg/logic arrays).