asynciterator/dist/taskscheduler.mjs

An asynchronous iterator library for advanced object pipelines.

const resolved = Promise.resolve(undefined);
// Returns a function that asynchronously schedules a task
export function createTaskScheduler() {
    // Use or create a microtask scheduler
    const scheduleMicrotask = typeof queueMicrotask === 'function' ?
        queueMicrotask : (task) => resolved.then(task);
    // Use or create a macrotask scheduler
    const scheduleMacrotask = typeof setImmediate === 'function' ?
        setImmediate : (task) => setTimeout(task, 0);
    // Interrupt with a macrotask every once in a while to avoid freezing
    let i = 0;
    let queue = null;
    return (task) => {
        // Tasks are currently being queued to avoid freezing
        if (queue !== null)
            queue.push(task);
        // Tasks are being scheduled normally as microtasks
        else if (++i < 100)
            scheduleMicrotask(task);
        // A macrotask interruption is needed
        else {
            // Hold all tasks in a queue, and reschedule them after a macrotask
            queue = [task];
            scheduleMacrotask(() => {
                // Work through the queue
                for (const queued of queue)
                    scheduleMicrotask(queued);
                queue = null;
                // Reset the interruption schedule
                i = 0;
            });
        }
    };
}