# std::stop_callback<Callback>::~stop_callback

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< cpp‎ | thread‎ | stop callback

~stop_callback(); |  | (since C++20)

Destroys the `stop_callback` object.

If *this has a `stop_token` with associated stop-state, deregisters the callback from it.

If the callback function is being invoked concurrently on another thread, the destructor does not complete until the callback function invocation is complete. If the callback function is being invoked on the same thread the destructor is being invoked on, then the destructor returns without waiting for callback invocation to complete (see Notes).

### Notes

The `stop_callback` destructor is designed to prevent race conditions and deadlocks. If another thread is currently invoking the callback, then the destructor cannot return until that completes, or else the function object could potentially be destroyed while it is being executed. The callback function is not required to be neither copyable nor movable - it lives in the `stop_callback` object itself even after registration.

On the other hand, if the current thread invoking the destructor is the same thread that is invoking the callback, then the destructor cannot wait or else a deadlock would occur. It is possible and valid for the same thread to be destroying the `stop_callback` while it is invoking its callback function, because the callback function might itself destroy the `stop_callback`, directly or indirectly.

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