On 28-09-22, 14:20, Bartosz Golaszewski wrote:
Ok, so this is not correct. The doc for gpiod_edge_event_buffer_get_event() says:
- @return Pointer to an event stored in the buffer. The lifetime of the
- event is tied to the buffer object. Users must not free the event
- returned by this function.
We make no guarantees that the address returned by gpiod_edge_event_buffer_get_event() will still be valid after a call to gpiod_line_request_read_edge_event(). In fact the doc for the latter says:
- @note Any exising events in the buffer are overwritten. This is not an
append operation.So we're being clear that after a call to gpiod_line_request_read_edge_event(), all previously returned edge event pointers are invalid unless the objects to which they point were explicitly copied.
Current implementation does indeed work like what you describe but that behavior is not "contractually" guaranteed and can change even between minor releases.
In C++ if you do:
const edge_event& ev = buffer.get_event(0); request.read_edge_event(buffer); std::cout << ev << std::endl;
You risk a segfault.
My understanding is that Rust should not allow a crash in this situation by design.
Hmm, so what exactly do we want to do here then ?
- Don't allow events to be referenced ? i.e. make event_clone() the default behavior ?
- Don't allow read_edge_event() to be called twice for a buffer ? that will be inefficient though.
- Somehow guarantee that reference to all the events are dropped before issuing read_edge_event() again, else make it fail ? I am not sure how straight forward that can be though.