described in documentation：
Identify types that require Zero Copy transfer over shared memory and annotate them with @transfer_mode(SHMEM_REF) in the IDL files.
Zero Copy transfer over shared memory requires the FlatData language binding when the type is variable-size.
So, if transfer variable-size data using shared memory, I need add @mutable。rti::flat::build_data(writer) will be used。
but, this sentence: Use the DataWriter’s get_loan() API to get a loaned sample for writing with Zero Copy。
my question：the conflict between rti::flat::build_data(writer) and get_loan(). Which method is used to structure the data?
In the case that your data type is
@mutable@language_binding(FLAT_DATA)
Then, you should use
rti::flat::build_data(writer)
to get the Builder object that you will use to populate the data sample/structure. You would not use the DataWriter::get_loan() API. The build_data() will return an object that internally has the loaned shared memory segment that it got from the DataWriter.
Thank you very much for your reply！
for example:
module test_types {
@mutable
@transfer_mode(SHMEM_REF)
@language_binding(FLAT_DATA)
struct CameraImage {
int64 timestamp;
string<128> test_string;
sequence<int32, 128> test_seq;
};
};
Transfer variable-size data using shared memory，based on your reply：
In addition to adding @mutable, and @language_binding(FLAT_DATA), do I need to add @transfer_mode(SHMEM_REF) ? why?
If you want to transfer that data structure using Zero Copy then you need to have the @transfer_mode(SHMEM_REF).
The @mutable and @language_binding(FLAT_DATA) is only additionally needed when the data structure has variable sized members.