NI DAQMX Using Callback Functions - ni/grpc-device GitHub Wiki
The C API has a few functions that take callback functions. These are:
The gRPC API implements these by making these functions server-streaming functions. For a sample of using these, see usages of DAQmxRegisterEveryNSamplesEvent and DAQmxRegisterDoneEvent in the analog-input-every-n-samples.py example.