Select in Groovy

The select functionality in Groovy can be simulated using concurrent programming features. Here’s an example that demonstrates a similar concept:

import java.util.concurrent.*

def c1 = new ArrayBlockingQueue(1)
def c2 = new ArrayBlockingQueue(1)

// Simulating concurrent operations
Thread.start {
    sleep(1000)
    c1.offer("one")
}

Thread.start {
    sleep(2000)
    c2.offer("two")
}

// Simulating select behavior
2.times {
    def result = null
    while (!result) {
        result = c1.poll(100, TimeUnit.MILLISECONDS) ?: c2.poll(100, TimeUnit.MILLISECONDS)
    }
    println "received $result"
}

In this example, we’re using ArrayBlockingQueue to simulate channels. The select behavior is simulated using a loop that polls both queues with a timeout.

Each queue will receive a value after some amount of time, simulating blocking operations executing in concurrent threads.

We use Thread.start to create new threads that will add values to the queues after a delay.

The main thread then waits for values from both queues simultaneously, printing each one as it arrives.

To run the program, save it as Select.groovy and use the groovy command:

$ groovy Select.groovy
received one
received two

We receive the values “one” and then “two” as expected.

Note that the total execution time is only ~2 seconds since both the 1 and 2 second sleep operations execute concurrently.

This example demonstrates how to simulate channel-like behavior and select operations in Groovy using Java’s concurrent utilities. While it’s not as elegant as Go’s native select statement, it achieves a similar result in terms of waiting on multiple concurrent operations.