How to create a sleep delay in nodejs that is Blocking

Question

I m currently trying to learn nodejs and a small project I m working is writing an API to control some networked LED lights   The microprocessor controlling the LEDs has a processing delay  and I need to space commands sent to the micro at least 100ms apart  In C  I m used to just calling Thread Sleep time   but I have not found a similar feature in node   I have found several solutions using the setTimeout      function in node  however  this is asynchronous and does not block the thread   which is what I need in this scenario    Is anyone aware of a blocking sleep or delay function  Preferably something that does not just spin the CPU  and has an accuracy of  -10 ms

User · Answer

asynchronous call ping command to block current code to execution in specified milliseconds    ping command is Cross-platform start  b means  start program but not show window    code as below   const   execSync     require  child process      delay blocking  specified milliseconds function sleep ms           special Reserved IPv4 Address RFC 5736   192 0 0 0        refer  https   en wikipedia org wiki Reserved IP addresses     execSync  start  b ping 192 0 0 0 -n 1 -w   ms   gt  nul         usage console log  delay 2500ms start t      new Date   getTime     1000  toFixed 3   sleep 2500  console log  delay 2500ms end t      new Date   getTime     1000  toFixed 3     notice important  Above is not a precision solution  it just approach the blocking time

User · Answer

I found something almost working here https   stackoverflow com questions 21819858 how-to-wrap-async-function-calls-into-a-sync-function-in-node-js-or-ja vascript   function AnticipatedSyncFunction        var ret      setTimeout function            var startdate   new Date           ret    hello    startdate        3000       while ret     undefined           require  deasync   runLoopOnce              return ret          var output   AnticipatedSyncFunction    var startdate   new Date   console log startdate  console log  output   output      The unique problem is the date printed isn t correct but the process at least is sequential

User · Answer

Easiest true sync solution  i e  no yield async  I could come up with that works in all OS s without any dependencies is to call the node process to eval an in-line setTimeout expression   const sleep    ms    gt  require  child process        execSync     process argv 0    -e setTimeout function       ms

User · Answer

The best solution is to create singleton controller for your LED which will queue all commands and execute them with specified delay   function LedController timeout      this timeout   timeout    100    this queue         this ready   true     LedController prototype send   function cmd  callback      sendCmdToLed cmd     if  callback  callback         or simply  sendCmdToLed cmd  callback   if sendCmdToLed is async     LedController prototype exec   function       this queue push arguments     this process        LedController prototype process   function       if  this queue length     0  return    if   this ready  return    var self   this    this ready   false    this send apply this  this queue shift       setTimeout function          self ready   true      self process         this timeout       var Led   new LedController      Now you can call Led exec and it ll handle all delays for you   Led exec cmd  function       console log  Command sent

User · Answer

Node is asynchronous by nature  and that s what s great about it  so you really shouldn t be blocking the thread  but as this seems to be for a project controlling LED s  I ll post a workaraound anyway  even if it s not a very good one and shouldn t be used  seriously    A while loop will block the thread  so you can create your own sleep function  function sleep time  callback        var stop   new Date   getTime        while new Date   getTime    lt  stop   time                        callback        to be used as  sleep 1000  function           executes after one second  and blocks the thread       I think this is the only way to block the thread  in principle   keeping it busy in a loop  as Node doesn t have any blocking functionality built in  as it would sorta defeat the purpose of the async behaviour

User · Answer

You can simply use yield feature introduced in ECMA6 and gen-run library   let run   require  gen-run      function sleep time        return function  callback            setTimeout function                console log time               callback               time             run function         console log  befor sleeping         yield sleep 2000       console log  after sleeping

User · Answer

use Node sleep package  https   www npmjs com package sleep   in your code you can use   var sleep   require  sleep     sleep sleep n    to sleep for a specific n seconds

User · Answer

With ECMA script 2017  supported by Node 7 6 and above   it becomes a one-liner   function sleep millis      return new Promise resolve   gt  setTimeout resolve  millis          Usage in async function async function test       await sleep 1000    console log  one second has elapsed         Usage in normal function function test2       sleep 1000  then      gt        console log  one second has elapsed

User · Answer

Just use child process execSync and call the system s sleep function     import child process module const child process   require  child process       Sleep for 5 seconds child process execSync  sleep 5        Sleep for 250 microseconds child process execSync  usleep 250        Sleep for a variable number of microseconds var numMicroSeconds   250  child process execFileSync  usleep    numMicroSeconds      I use this in a loop at the top of my main application script to make Node wait until network drives are attached before running the rest of the application

User · Answer

It s pretty trivial to implement with native addon  so someone did that  https   github com ErikDubbelboer node-sleep git

User · Answer

Blocking in Node js is not necessary  even when developing tight hardware solutions   See temporal js which does not use setTimeout or setIntervalsetImmediate   Instead  it uses setImmediate or nextTick which give much higher resolution  task execution  and you can create a linear list of tasks   But you can do it without blocking the thread

User · Answer

blocking the main thread is not a good style for node because in most cases more then one person is using it  You should use settimeout setinterval in combination with callbacks

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