dora/coordinator/README.md

• Coordinator
• • Try it out

Coordinator

Prototype for a process/library-based dora-rs implementation, instead of framework-based. The idea is that each operator is compiled as a separate executable. The dora-coordinator runtime is responsible for reading the dataflow descriptor file and launching the operators accordingly. The operators use a common library called dora-api, which implements the communication layer based on zenoh.

This approach has the following advantages:

• Less overhead
  • No data transfer between a runtime and the operator
  • The compiler can inline and optimize the full process
• More flexibility
  • Operators can be sync or async
  • They can decide how many threads and which execution model they use
  • The OS ensures fair share of resources (e.g. CPU time) -> no need to cooperate with other operators
  • Operators get all inputs immediately -> no need for input rules
  • Keeping local state is easily possible
• Separate address spaces
  • The operators are isolated from each other.

There are drawbacks too, for example:

• Less control
  • Processes run independently -> need to cooperate with the runtime, e.g. on stop signals
  • Operator migration is more difficult
• Operators are always isolated
  • No way of using in-memory channels
  • Local sockets and shared memory should be still possible

Try it out

• Compile the dora runtime using cargo build -p dora-runtime --release
• Compile the nodes in examples using cargo build -p dora-coordinator --examples --release
• Compile the Rust example operator through cargo build --manifest-path ../runtime/examples/example-operator/Cargo.toml --release
• Compile the C example operator through:
  • cd ../runtime/examples/c-operator
  • cp ../../../api/c/operator/api.h .
  • clang -c operator.c
  • clang -shared -v operator.o -o operator.so
• Run the mini-dataflow example using cargo run --release -- run examples/mini-dataflow.yml
  • This spawns a timer source, which sends the current time periodically, and a logger sink, which prints the incoming data.
  • The timer will exit after 100 iterations. The other nodes/operators will then exit as well because all sources closed.