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Simulator Structure

It emulates an ONT device controlled by the ReadUntil API directly or via gRPC. It takes full-length reads and terminates them early, as necessary.

Class Hierarchy

The class hierarchy is as follows

# A -> B means that B inherits from A.

ChannelElement -> ShortGap, LongGap, MuxScan, UnblockDelay, ChunkedRead, NoReadLeftGap

ChunkedRead: an active read that is split into chunks

Channel: repeatedly selects a new channel element

ReadPool -> ReadPoolFromIterable, ReadPoolFromFile, ReadPoolFromIterable

ReadsWriter -> SingleFileReadsWriter, ArrayReadsWriter, RotatingFileReadsWriter

ONTDeviceServicer: gRPC servicer that delegates calls to an underlying ONTSimulator device

ReadUntilDevice: abstract class representing device that allows to start/stop an experiment, block/stop receiving reads, get read chunks
ReadUntilDevice -> ONTSimulator: simulating a given number of channels
               \-> SimulatorGRPCClient: takes server port as argument, connects to a gRPC server that has service ONTDeviceServicer

Developer Notes

We use gRPC because it makes serialization easy, is efficient, allows streaming, and works across languages. After changing the .proto file, you can recompile it with:

# activate python environment with gRPC
# requires gnu sed (brew install gnu-sed) or use: sed -i ''

cd src/simreaduntil/simulator
rm -rf protos_generated
mkdir protos_generated
# replace imports so they work with the project structure ("ont_simulator" must be on the python path)
python -m grpc_tools.protoc -Iprotos/ --python_out=protos_generated/ --pyi_out=protos_generated/ --grpc_python_out=protos_generated/ protos/ont_device.proto && \
    sed -i -E "s%import (.*)_pb2 as%import simreaduntil.simulator.protos_generated.\1_pb2 as%g" protos_generated/ont_device_pb2_grpc.py

# not working:
# cd src && python -m grpc_tools.protoc -Isimreaduntil/simulator/protos/ --python_out=simreaduntil/simulator/protos_generated/ --pyi_out=simreaduntil/simulator/protos_generated/ --grpc_python_out=simreaduntil/simulator/protos_generated/ simreaduntil/simulator/protos/ont_device.proto

Debugging the gRPC server

You can run the tests with pytest to see whether it is working. Try to execute the files without pytest to check that the imports work.

You can check that gRPC networking works by looking at the example_grpc directory.

Moreover, gRPC logging can be enabled with

export GRPC_VERBOSITY=DEBUG
export GRPC_TRACE=all

It may happen that the previous gRPC server instantiation did not terminate properly. In this case, you can kill the process with:

# find relevant python processes via
lsof -i tcp | grep Python

# if you know the port, e.g. 10871
netstat -an | grep 10871
sudo lsof -i :10871
#sudo kill -9 <PID>