Worker Pools in Modelica

Our example demonstrates how to implement a worker pool using Modelica’s synchronization and concurrency features.

model WorkerPool
  constant Integer numJobs = 5;
  constant Integer numWorkers = 3;
  
  class Job
    Integer id;
    Boolean finished = false;
  end Job;
  
  Job[numJobs] jobs;
  Integer[numJobs] results;
  Integer jobsCompleted = 0;
  
  function worker
    input Integer id;
    input Job job;
    output Integer result;
  algorithm
    print("worker " + String(id) + " started job " + String(job.id));
    Modelica.Utilities.System.sleep(1);
    print("worker " + String(id) + " finished job " + String(job.id));
    result := job.id * 2;
    job.finished := true;
  end worker;
  
equation
  when jobsCompleted == numJobs then
    terminate("All jobs completed");
  end when;
  
algorithm
  // Initialize jobs
  for i in 1:numJobs loop
    jobs[i].id := i;
  end for;
  
  // Start workers
  for w in 1:numWorkers loop
    Modelica.Utilities.Streams.print("Starting worker " + String(w));
    for j in 1:numJobs loop
      when pre(not jobs[j].finished) then
        results[j] := worker(w, jobs[j]);
        jobsCompleted := jobsCompleted + 1;
      end when;
    end for;
  end for;
end WorkerPool;

In this Modelica implementation, we create a WorkerPool model that simulates a worker pool with concurrent job processing. Here’s a breakdown of the code:

1. We define constants for the number of jobs and workers.

2. A Job class is created to represent each job with an id and a finished status.

3. We create arrays to store jobs and results, and a counter for completed jobs.

4. The worker function simulates the work done by each worker. It takes a job, prints start and finish messages, sleeps for a second to simulate work, and returns a result.

5. We use an equation to terminate the simulation when all jobs are completed.

6. In the algorithm section, we initialize the jobs and start the workers.

7. For each worker, we use when statements to process unfinished jobs. This simulates concurrent execution in Modelica.

8. When a job is finished, we store the result and increment the jobsCompleted counter.

To run this model, you would typically use a Modelica simulation environment. The output would show jobs being processed by different workers, similar to the original example.

Note that Modelica doesn’t have built-in constructs for true parallel execution like Go’s goroutines. This implementation simulates concurrency within Modelica’s equation-based paradigm. In a real-world scenario, the actual parallelism would depend on the Modelica tool’s capabilities and the underlying hardware.