How to sleep the thread in node.js without affecting other threads?
As per Understanding the node.js event loop, node.js supports a single thread model. That means if I make multiple requests to a node.js server, it won't spawn a new thread for each request but will execute each request one by one. It means if I do the following for the first request in my node.js code, and meanwhile a new request comes in on node, the second request has to wait until the first request completes, including 5 second sleep time. Right?
var sleep = require('sleep');
sleep.sleep(5)//sleep for 5 seconds
Is there a way that node.js can spawn a new thread for each request so that the second request does not have to wait for the first request to complete, or can I call sleep on specific thread only?
If you are referring to the npm module sleep, it notes in the readme that sleep will block execution. So you are right - it isn't what you want. Instead you want to use setTimeout which is non-blocking. Here is an example:
setTimeout(function() {
console.log('hello world!');
}, 5000);
For anyone looking to do this using es7 async/await, this example should help:
const snooze = ms => new Promise(resolve => setTimeout(resolve, ms));
const example = async () => {
console.log('About to snooze without halting the event loop...');
await snooze(1000);
console.log('done!');
};
example();
In case you have a loop with an async request in each one and you want a certain time between each request you can use this code:
var startTimeout = function(timeout, i){
setTimeout(function() {
myAsyncFunc(i).then(function(data){
console.log(data);
})
}, timeout);
}
var myFunc = function(){
timeout = 0;
i = 0;
while(i < 10){
// By calling a function, the i-value is going to be 1.. 10 and not always 10
startTimeout(timeout, i);
// Increase timeout by 1 sec after each call
timeout += 1000;
i++;
}
}
This examples waits 1 second after each request before sending the next one.
Please consider the deasync module, personally I don't like the Promise way to make all functions async, and keyword async/await anythere. And I think the official node.js should consider to expose the event loop API, this will solve the callback hell simply. Node.js is a framework not a language.
var node = require("deasync");
node.loop = node.runLoopOnce;
var done = 0;
// async call here
db.query("select * from ticket", (error, results, fields)=>{
done = 1;
});
while (!done)
node.loop();
// Now, here you go
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