Function apr_queue_trypop 

pub unsafe extern "C" fn apr_queue_trypop(
    queue: *mut apr_queue_t,
    data: *mut *mut c_void,
) -> apr_status_t

pop/get an object to the queue, returning immediately if the queue is empty

@param queue the queue @param data the data @returns APR_EINTR the blocking operation was interrupted (try again) @returns APR_EAGAIN the queue is empty @returns APR_EOF the queue has been terminated @returns APR_SUCCESS on a successful pop