CODEWITHSUNDEEP
javascriptnode.jsexpressasynchronous
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Reputation: 381

Send response and continue to perform tasks Express | Node.js

In Node.js (which I'm new to) I am trying to perform a series of tasks after receiving a response. However, I want to make the response time as fast as possible. I don't need to return the results of these tasks to the client, so I'm trying to return the response immediately.

My current implementation is roughly:

var requestTime = Date.now; 

app.post('/messages', function (req, res) {
  console.log("received request");

  // handle the response
  var body = res.body;
  res.send('Success');
  res.end();
  console.log("sent response");

  performComplexTasks(body)
})

function performComplexTasks(body){
   // perform data with body data here;
   console.log("finished tasks:", Date.now()-requestTime, "ms");
}

// -------LOG-----------
//    received request
//    POST /api/messages 200 3.685 ms - 59
//    sent response
//    finished tasks: 2500ms

The client making the request seems to hang until performComplexTasks() is finished. (The POST finishes in 3.685ms, but the response takes 2500ms to finish.)

Is there a way to send the response immediately and complete other tasks without having the client wait/hang? (In my case, the client cannot make multiple API calls.)

Upvotes: 37

Views: 30265

Answers (2)

user6269864
user6269864

Reputation:

If your job is not super-CPU-intense and you can tolerate some work on the main server thread, then just use await to break the execution so that the request can be properly sent. You can use setTimeout or await.

// This line is wrong too - ask a separate question if needed
var requestTime = Date.now; 

app.post('/messages', async function (req, res) {
  console.log("received request");

  // handle the response
  var body = res.body;
  res.status(200).send({ success: true });
  console.log("sent response");

  // Method 1:
  await performComplexTasks(body)

  // Method 2:
  setTimeout(() => performComplexTasks(body), 0);
})

async function performComplexTasks(body){
   // The line below is required if using the `await` method -
   // it breaks execution and allows your previous function to
   // continue, otherwise we will only resume the other function after
   // this function is completed.
   await new Promise(resolve => setTimeout(resolve, 1));

   // perform data with body data here;
   console.log("finished tasks:", Date.now()-requestTime, "ms");
}

This isn't really a fantastic solution and you'd need to use worker threads for long operations.

Upvotes: 20

teq
teq

Reputation: 1594

Am I right that you're trying to execute a CPU-intensive job in performComplexTasks? If so, then event loop is being locked by that task and new requests are waiting until the job is finished.

It's a bad practice in node.js to execute such 'complex' tasks in the same process as http server. Consider using background workers, queues or something like that.

See this topic for details: Node.js and CPU intensive requests

Upvotes: 11

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