When the data(parameter in am_recv_callback) will be freed or marked resuable?

[XCloudAI]

For active message API, there's below API will be called when receving the data from peer side:
https://github.com/openucx/ucx/blob/v1.10.1/test/apps/iodemo/ucx_wrapper.cc#L465

ucs_status_t UcxContext::am_recv_callback(void *arg, const void *header,
                                          size_t header_length,
                                          void *data, size_t length,
                                          const ucp_am_recv_param_t *param)

After the void *data has been copied, who's responsible for releasing the space or mark it could be resuable?
https://github.com/openucx/ucx/blob/v1.10.1/test/apps/iodemo/ucx_wrapper.cc#L643

    if (!(data_desc._param->recv_attr & UCP_AM_RECV_ATTR_FLAG_RNDV)) {
        memcpy(buffer, data_desc._data, length);
        (*callback)(UCS_OK);
        return true;
    }

[yosefe]

UcxContext::am_recv_callback function is part of io_demo test application, not UCX core library. For documentation of active messages API, please see https://github.com/openucx/ucx/blob/master/src/ucp/api/ucp_def.h#L669 - the "void *data" will be released according to the return value of the active message callback.

[XCloudAI]

@yosefe
Take io_demo for example:

1. set active message callback here:
   https://github.com/openucx/ucx/blob/v1.10.1/test/apps/iodemo/ucx_wrapper.cc#L142

    if (_use_am) {
        set_am_handler(am_recv_callback, this);
    } else {
        recv_io_message();
    }

2. the am_recv_callback will always return UCS_OK
   https://github.com/openucx/ucx/blob/v1.10.1/test/apps/iodemo/ucx_wrapper.cc#L490

    self->dispatch_am_message(conn, header, header_length, data_desc);

    return UCS_OK

@yosefe So, after am_recv_callback is called, the void *data will be released, right?
If so, is there some method to cache the void *data space, then the user could call some API to release it to UCX library.
The reason that I want to do this is because:
After am_recv_callback is retured, the void *data space will be released. So, I need to copy the data into one cache space first (assume its name is am_cache). In some scenario, I need to trigger the other component to read the received data. So I copy the data from am_cache again. In such case, I do one time extra copy. If the void *data could be cached and controled by user to decied when releasing it to UCX, then It could save one time of copy operation.

[XCloudAI]

@yosefe What's about the usage of UCP_AM_RECV_ATTR_FLAG_DATA? Could I use it to control that the void *data could serverd by user and release it to UCX later?

[yosefe]

if UCP_AM_RECV_ATTR_FLAG_DATA flag is present, that it's possible to return UCS_INPROGRESS from the active message handler, and release it later by ucp_am_data_release

[changchengx]

@XCloudAI
|> The reason that I want to do this is because:

Could you show me the code in your project?

[XCloudAI]

Just school's homework. I've graduated these days.