RecurringTask.js

RecurringTask.js

// Utility for running recurring tasks
// Uses setInterval and setTimeout
// Has ability to schedule the first run instantly or wait for a fixed MS


export default class RecurringTask {
    constructor({
        task, // can be async
        intervalMs = 1000, // interval in milliseconds
        lastRun = 0, // 0 == run immediately

        // mode can be "gap" or "strict" or "hybrid"
        // "strict" (overlap) will run every intervalMs religiously, even if that means overlapping with prior tasks that take longer than intervalMs to execute
        // "gap" (no overlap, wait) will only schedule the next task for intervalMs AFTER the previous task has concluded. There will never be execution overlap, and the intervalMs gap will always be maintained
        // "hybrid" (no overlap, run asap) will act like "strict" mode BUT will never overlap. If a task's execution time exceeds intervalMs, it will wait until that task completes and then immediately begin the next task.
        mode = 'gap' // gap is the safest default for most situations
    })
    {
        this.task = task
        this.intervalMs = intervalMs
        this.lastRun = lastRun
        this.mode = mode
    }

    get timeUntilNextRun(){
        return Math.max(this.intervalMs - (Date.now() - this.lastRun), 0)
    }

    // Schedule the first run
    start(){
        setTimeout(this.safeRunTask.bind(this), this.timeUntilNextRun)
    }

    // Runs right before a task is attempted
    before(){
        if (this.mode == 'strict' || this.mode == 'hybrid')
            this.lastRun = Date.now()

        if (this.mode == 'strict')
            setTimeout(this.safeRunTask.bind(this), this.intervalMs)
    }

    // Runs right after a task is attempted
    after(){
        if (this.mode == 'gap'){
            this.lastRun = Date.now()
            setTimeout(this.safeRunTask.bind(this), this.intervalMs)
        }

        if (this.mode == 'hybrid')
            setTimeout(this.safeRunTask.bind(this), this.timeUntilNextRun)
    }

    async safeRunTask(){
        this.before()
        try { await this.task() }
        catch (e) { }
        this.after()
    }
}



// import { sleep } from './sleep'

// test()
// async function test(){
    
//     const task = new RecurringTask({
//         intervalMs: 1000,
//         lastRun: 0, // Date.now(),
//         mode: 'hybrid',
//         async task(){
//             const ID = Math.round(Math.random() * 10000)
//             console.log(`Begin task ${ID}`)
//             await sleep(2000)
//             console.log(`End task ${ID}`)
//         }
//     })

//     task.start()

// }