Scheduling protocol

During simulations, the simulator and the scheduler process are in constant communication. The scheduling protocol defines which data the processes exchange when.

Do not confuse the scheduling protocol with the communication protocol. The scheduling protocol does not define how the data is exchanged.

ElastiSim invokes the scheduling algorithm periodically in a user-defined interval or at events such as job submissions or scheduling points (see Configuration for all options). Each invocation contains a list of compute nodes, jobs, and a map holding system information. After the scheduling algorithm makes a scheduling decision, the scheduler process forwards the decision to the simulator process, applying the new schedule.

The entire simulation stops at invocation time and continues after the scheduling algorithm returns.

The following sequence diagram visualizes the scheduling protocol.

sequenceDiagram
    participant sim as Simulator
    participant sched as Scheduler
    critical establish connection
        sim-->sched: connect
    end
    sim->>sim: start simulation
    activate sim
    loop at each invocation trigger<br>or every <scheduling interval><br>while simulation is running
        sim->>sched: invoke
        deactivate sim
        activate sched
        sched->>sched: schedule
        sched->>sim: forward schedule
        deactivate sched
        activate sim
        sim->>sim: apply schedule
    end
    sim->>sched: finalize
    sim->>sim: finalize
    deactivate sim

ElastiSim employs ZeroMQ to establish the connection and exchange data following the scheduling protocol. This design choice separates the concerns and allows ElastiSim to interface with any modern programming language. Users can develop scheduling algorithms in languages such as Python, while the entire simulation makes use of highly performant C++ routines. The Scheduling interface section documents the details of exchanged data, all available interfaces, and their routines.