Closing Channels in Fortress

In Java, we can simulate channels using concurrent queues and thread synchronization. Here’s an example that demonstrates the concept of closing channels:

import java.util.concurrent.BlockingQueue;
import java.util.concurrent.LinkedBlockingQueue;

public class ClosingChannels {
    public static void main(String[] args) throws InterruptedException {
        BlockingQueue<Integer> jobs = new LinkedBlockingQueue<>(5);
        BlockingQueue<Boolean> done = new LinkedBlockingQueue<>();

        // Here's the worker thread. It repeatedly takes from 'jobs'.
        // We use a special marker (null) to indicate that the channel is closed.
        Thread worker = new Thread(() -> {
            while (true) {
                try {
                    Integer job = jobs.take();
                    if (job == null) {
                        System.out.println("received all jobs");
                        done.put(true);
                        return;
                    }
                    System.out.println("received job " + job);
                } catch (InterruptedException e) {
                    Thread.currentThread().interrupt();
                    return;
                }
            }
        });
        worker.start();

        // This sends 3 jobs to the worker over the 'jobs' queue, then "closes" it.
        for (int j = 1; j <= 3; j++) {
            jobs.put(j);
            System.out.println("sent job " + j);
        }
        jobs.put(null);  // Signal that no more jobs will be sent
        System.out.println("sent all jobs");

        // We await the worker using the synchronization approach.
        done.take();

        // Checking if the channel is closed (empty in this case)
        boolean moreJobs = !jobs.isEmpty();
        System.out.println("received more jobs: " + moreJobs);
    }
}

In this example, we use BlockingQueue to simulate channels. The jobs queue represents the channel for sending jobs, and the done queue is used for synchronization.

The worker thread continuously takes jobs from the jobs queue. We use a special marker (null) to indicate that no more jobs will be sent, simulating a closed channel.

We send 3 jobs to the worker, then send the special marker to indicate we’re done sending jobs. The worker processes these jobs and signals completion through the done queue.

Finally, we check if there are any more jobs in the queue, which is equivalent to checking if a channel is closed and empty in Go.

To run this program:

$ javac ClosingChannels.java
$ java ClosingChannels
sent job 1
received job 1
sent job 2
received job 2
sent job 3
received job 3
sent all jobs
received all jobs
received more jobs: false

This example demonstrates how to simulate channel closing and synchronization in Java, although it’s worth noting that Java’s concurrency model is different from Go’s, and this is an approximation of the behavior.

Non Blocking Channel Operations in Fortress

Range Over Channels in Fortress

Learn X By Example

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Closing Channels in Fortress