@prelude/channel/mjs/select.js

Channel module.

import { Channel, ReadAttempt, WriteAttempt } from './channel.js';
export async function* select(...attempts) {
    while (true) {
        const result = await selectNext(...attempts);
        if (result.done) {
            break;
        }
        yield result.value;
    }
}
export async function selectNext(...attempts) {
    return selectSync(attempts) ?? await selectAsync(attempts);
}
export function selectAsync(attempts) {
    return new Promise((resolve, reject) => {
        const undos = [];
        for (const attempt of attempts) {
            if (attempt instanceof Channel) {
                undos.push(attempt.pushRead(result => {
                    undos.forEach(undo => undo());
                    resolve(result);
                }));
            }
            else if (attempt instanceof WriteAttempt) {
                undos.push(attempt.channel.pushWrite({ value: attempt.value, enqueued: (err) => {
                        undos.forEach(_ => _());
                        if (err) {
                            reject(err);
                            return;
                        }
                        resolve(attempt.perform(attempt.value));
                    } }));
            }
            else if (attempt instanceof ReadAttempt) {
                undos.push(attempt.channel.pushRead(result => {
                    undos.forEach(undo => undo());
                    resolve(attempt.perform(result));
                }));
            }
            else {
                throw new Error('Invalid attempt.');
            }
        }
    });
}
export function selectSync(attempts) {
    const n = attempts.length;
    for (let i = 0; i < n; i++) {
        const j = i + Math.floor(Math.random() * (n - i));
        const attempt = attempts[j];
        if (attempt instanceof Channel) {
            if (attempt.pendingWrites > 0) {
                return { value: attempt.consumeWrite() };
            }
        }
        else if (attempt instanceof WriteAttempt) {
            if (attempt.channel.cap === 0 && attempt.channel.pendingReads > 0) {
                attempt.channel.consumeRead({ value: attempt.value });
                return attempt.perform(attempt.value);
            }
            else if (attempt.channel.pendingWrites < attempt.channel.cap) {
                attempt.channel.pushWrite({ value: attempt.value });
                return attempt.perform(attempt.value);
            }
        }
        else if (attempt instanceof ReadAttempt) {
            if (attempt.channel.pendingWrites > 0) {
                const value = attempt.channel.consumeWrite();
                return attempt.perform({ value });
            }
        }
        else {
            throw new Error('Invalid attempt.');
        }
        attempts[j] = attempts[i];
        attempts[i] = attempt;
    }
    return;
}
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