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Channel selector

Select

Selectors provide an option for the user to wait on multiple channels and take appropriate action based on which channel the message appears. The thread executing the select blocks until there is a message that appears in one of the channels and executes the appropriate action for that message and returns.

class Selector {
    <T1, T2> void selectorTest(Channel<T1> chan1,
                               Channel<T2> chan2) {
        Selector selector = selector(selectCase(
            chan1, t1 -> {
                // do something
            }),
            selectCase(chan2, t2 -> {
                // do something else
            })
        );
        selector.select();
    }
}

Until Done

Selector also expose a untilDone method, calls select in a loop, waiting for a message on any of the channel and then taking the corresponding action. This loop continues executing until all the channels have been closed and completely read. Once the call returns from this method the Selector object is closed and cannot be further used for any other call.

There are two special action that are defined in theSelector class: Selector.BREAK_ACTION and Selector.CONTINUE_ACTION. If a channel is associated with the break action, and a message appears on that channel, the untilDone loop is broken, and the method returns to the caller. The continue action acts like a pass statement, it basically means take no action if a message appears on that channel and wait for the next message on some other channel.

class Selector {
    <T1, T2> void untilDoneTest(Channel<T1> chan1, Channel<T2> chan2,
                                Channel<String> exitChan) {
        Selector selector = selector(selectCase(
            chan1, t1 -> {
                // do something
            }),
            selectCase(chan2, t2 -> {
                // do something else
            }),
            selectCase(exitChan, Selector.BREAK_ACTION)
        );
        // This method will keep on executing the corresponding 
        // actions as message keeps on appearing in chan1 and chan2. 
        // On a message in exitChan, it executes the BREAK_ACTION
        // which will break the loop and return to the caller.
        selector.untilDone();
    }
}

Default Action

Sometimes, there is a need to execute a default action when there is no message in any of the channels. To achieve this, Selector exposes untilOrDefault method. It works exactly like the untilDone method, but additionally takes a null-ary action which is executed when there is no message in any of the channels.

class Selector {
    <T1, T2> void untilDoneTest(Channel<T1> chan1, Channel<T2> chan2,
                                Channel<String> exitChan) {
        Selector selector = selector(selectCase(
            chan1, t1 -> {
                // do something
            }),
            selectCase(chan2, t2 -> {
                // do something else
            }),
            selectCase(exitChan, Selector.BREAK_ACTION)
        );
        // This method will keep on executing the corresponding actions 
        // as message keeps on appearing in chan1 and chan2. 
        // On a message in exitChan, it executes the BREAK_ACTION which will 
        // break the loop and return to the caller.
        selector.untilOrDefault(() -> {
            // do default action handling
        });
    }
}

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