NSchedule
An efficient periodic task scheduler with concurrency limits.
Features
- Limits the nunmber of concurrently executing tasks. This avoids overloading the resource used by the task (a server or network link, for example).
- Efficiently schedules tasks that must be repeated periodically.
- Individual tasks are rescheduled after they have run. This prevents multiple invocations of the same task from overlapping.
- Allows any combination of: immediate/delayed and periodic/one-shot.
Related Packages
Some other packages you might want to consider.
- agenda Database-backed cron-like scheduler.
- flagpoll Supports a finite number of task executions (will not reschedule a task indefinitely).
- node-schedule Cron-like scheduling. From the readme: 'node-schedule is for time-based scheduling, not interval-based scheduling.'
- poll Work in progress.
- pomelo-schedule Allows cron syntax. No concurrency limits. For example, schedule 100 tasks with different intervals in the same section of code and all 100 will trigger immediately.
- simple-schedule All tasks must have the same interval and do not recur.
Installation
npm install nschedule
Common Usage
#! /usr/bin/env node // --------------------------------------------------------------------------- // Demonstrates some common scheduling frequency and recurrence patterns. // --------------------------------------------------------------------------- var Scheduler = require('nschedule'); // Create a scheduler that will not execute more than 2 tasks // at a time. var scheduler = new Scheduler(2); // This task recurs every 3 seconds. scheduler.add(3000, function(done){ console.log("Task at period 3s. " + (new Date).toISOString()); done(); }); // This task recurs every 5 seconds. scheduler.add(5000, function(done){ console.log("Task at period 5s. " + (new Date).toISOString()); done(); }); // This task executes once after 15 seconds. scheduler.add(15000, function(done){ console.log("Task at period 15s. " + (new Date).toISOString()); done(scheduler.STOP); }); // This task executes immediately and does not recur. // The interval is effectively ignored. scheduler.add(1000, function(done){ console.log("One shot task. " + (new Date).toISOString()); // Stop after first and only execution. done(scheduler.STOP); }, scheduler.IMMEDIATE); Concurrency Limiting Example
#! /usr/bin/env node // --------------------------------------------------------------------------- // Demonstrates the limit on concurrently executing tasks. // --------------------------------------------------------------------------- var Scheduler = require('nschedule'); var TICK_IN_MS = 100; // Create a scheduler that will not execute more than 1 task // at a time. var scheduler = new Scheduler(1); // This task recurs every second but will be blocked for executing by the long // running task schedule every 5s. scheduler.add(1000, function(done){ logWithTimestamp('Task at 1s *'); done(); }); // This task is scheduled to recur every 5s but also takes 5s to execute, so it // will actually execute every 10s. // // As the scheduler was created with a concurrency setting of 1, when this task // executes it will block the task that runs every 1s while it is executing. // To prevent this behavior, create the scheduler with a higher concurrency // setting. scheduler.add(5000, function(done){ logWithTimestamp('Task at 10s ********** (start)'); busy('Task at 10s ********** (end)', 5000, done); }); // Simulate some operation that takes time to complete (backing up a database or // network communications, for exanple). function busy(name, interval, done){ if(interval <= 0){ logWithTimestamp(name); done(); return; } setTimeout(function(){ busy(name, interval - TICK_IN_MS, done); }, TICK_IN_MS); } function logWithTimestamp(name){ console.log((new Date).toISOString() + " " + name); }