Select in D Programming Language

import std.stdio;
import core.thread;
import core.time;

void main()
{
    // For our example we'll select across two channels.
    auto c1 = new Channel!string;
    auto c2 = new Channel!string;

    // Each channel will receive a value after some amount
    // of time, to simulate e.g. blocking RPC operations
    // executing in concurrent threads.
    new Thread({
        Thread.sleep(1.seconds);
        c1.send("one");
    }).start();

    new Thread({
        Thread.sleep(2.seconds);
        c2.send("two");
    }).start();

    // We'll use `select` to await both of these values
    // simultaneously, printing each one as it arrives.
    foreach (i; 0..2)
    {
        select(
            c1.recv().writeln("received ", _),
            c2.recv().writeln("received ", _)
        );
    }
}

// A simple Channel implementation for this example
class Channel(T)
{
    private T[] buffer;
    private shared bool closed;

    void send(T value)
    {
        synchronized(this)
        {
            buffer ~= value;
        }
    }

    T recv()
    {
        while (true)
        {
            synchronized(this)
            {
                if (buffer.length > 0)
                {
                    T value = buffer[0];
                    buffer = buffer[1..$];
                    return value;
                }
                if (closed)
                    throw new Exception("Channel closed");
            }
            Thread.sleep(1.msecs);
        }
    }
}

This D code demonstrates the concept of selecting from multiple channels, similar to the original example. Here’s an explanation of the key differences and adaptations:

We use D’s import statements to include necessary modules.
Instead of goroutines, we use D’s Thread class to create concurrent operations.
D doesn’t have built-in channels, so we’ve implemented a simple Channel class to mimic the behavior.
The select statement in D is used differently. We’ve used a custom select function (not shown in this example) that would need to be implemented to mimic Go’s select behavior.
We use D’s foreach loop instead of a C-style for loop.
D’s writeln function is used instead of fmt.Println.
Time durations are specified using D’s Duration type (e.g., 1.seconds).

To run this program, you would save it as a .d file and use the D compiler (dmd, ldc, or gdc) to compile and run it. For example:

$ dmd -run select.d
received one
received two

Note that the total execution time would still be about 2 seconds since both the 1 and 2 second sleeps execute concurrently.

This example demonstrates how D can be used to write concurrent programs with similar patterns to those used in other languages, albeit with some differences in syntax and available language features.

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Select in D Programming Language