Closing Channels in Cilk

#include <cilk/cilk.h>
#include <iostream>

int main() {
    // Create a channel-like structure using std::queue
    std::queue<int> jobs;
    std::atomic<bool> done(false);

    // This is our worker function, similar to a goroutine
    cilk_spawn [&]() {
        while (true) {
            int j;
            bool more = false;
            
            // Simulate channel receive
            {
                std::lock_guard<std::mutex> lock(mutex);
                if (!jobs.empty()) {
                    j = jobs.front();
                    jobs.pop();
                    more = true;
                }
            }

            if (more) {
                std::cout << "received job " << j << std::endl;
            } else {
                if (done.load()) {
                    std::cout << "received all jobs" << std::endl;
                    return;
                }
            }
        }
    }();

    // Send 3 jobs to the worker
    for (int j = 1; j <= 3; j++) {
        {
            std::lock_guard<std::mutex> lock(mutex);
            jobs.push(j);
        }
        std::cout << "sent job " << j << std::endl;
    }

    // Signal that we've sent all jobs
    done.store(true);
    std::cout << "sent all jobs" << std::endl;

    // Wait for the worker to finish
    cilk_sync;

    // Check if the channel is empty (closed in Go terms)
    bool ok;
    {
        std::lock_guard<std::mutex> lock(mutex);
        ok = !jobs.empty();
    }
    std::cout << "received more jobs: " << (ok ? "true" : "false") << std::endl;

    return 0;
}

In this example, we demonstrate how to simulate channel closing in Cilk, which doesn’t have built-in channel support like Go. We use a combination of std::queue, std::mutex, and std::atomic to achieve similar functionality.

Here’s a breakdown of the code:

We create a std::queue called jobs to simulate a channel, and an std::atomic<bool> called done to signal when all jobs have been sent.
The worker function is spawned using cilk_spawn. It continuously checks for jobs in the queue and processes them. When done is set to true and the queue is empty, it prints “received all jobs” and exits.
In the main function, we send 3 jobs to the worker by pushing them onto the jobs queue.
After sending all jobs, we set done to true to signal that no more jobs will be sent.
We use cilk_sync to wait for the worker to finish processing all jobs.
Finally, we check if there are any more jobs in the queue, which is equivalent to checking if a channel is closed in Go.

To compile and run this Cilk program, you would typically use:

$ clang++ -fcilkplus closing_channels.cpp -o closing_channels
$ ./closing_channels

The output would be similar to the Go version, showing the jobs being sent and received, and finally indicating that all jobs have been processed.

This example demonstrates how to implement a pattern similar to closing channels in Go using Cilk and C++ constructs. While Cilk doesn’t have built-in channels, we can achieve similar functionality using standard C++ concurrency primitives.

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Closing Channels in Cilk