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Exit Process When all Readline on('line') Callbacks Complete

0

I have a Node v10.14.1 program that reads a CSV file line-by-line using the readline Interface

My .on('line') is an async callback performs some operations which read/write from a db, thus I use async/await to deal with the promises.

A short version of the program's code block of interest would look something like:

const readline = require('readline');
const filesystem = require('fs');

const reader = readline.createInterface(
 input: filesystem.createReadStream(pathToSomeCSV)
);

reader.on('line', async (line) => 
 await doSomeDBStuff();
)

If I leave the above the way it is, the process does not exit. However, if I

reader.on('close', () => process.exit());

then the process exits prior to all of the on('line') callbacks finishing and their promises resolving.

My question is: is there a way to say "Upon all lines being read AND all on('line') callbacks being completed with their promises resolved, then exit the process (I assume with process.exit())"?

node.js promise async-await

share|improve this question

asked Mar 7 at 14:10

northsideknightnorthsideknight

8891720

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  Just drop the close handler. When all asynchronous work is done (and there are no outstanding handler), node.js will stop by itself. You don't need to call process.exit() explicitly, that's only useful for prematurely exiting (or exiting with a specific error code). You should investigate why your process does not end, is some db connection kept open?
  
  – Bergi
  Mar 7 at 14:15
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  so it is an open db connection pool that is causing the process not to exit. I still have the problem but it could be worded differently because it is a problem with db library (sequelize) not readline.
  
  – northsideknight
  Mar 7 at 15:28
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Yeah. Is there a method that drains sequelizes connection pool? You could call that in the close handler.
  
  – Bergi
  Mar 7 at 15:44
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  I could not find one. What we ended up doing was, for every operation that needs to occur asynchronously, we added a promise to an array that would resolve when that operation completed. Then, upon close we used await Promise.all(operations), when that finished, we explicitly closed the Sequelize connection pool.
  
  – northsideknight
  Mar 8 at 14:14
  

  
  
  
  

add a comment | 

0

I have a Node v10.14.1 program that reads a CSV file line-by-line using the readline Interface

My .on('line') is an async callback performs some operations which read/write from a db, thus I use async/await to deal with the promises.

A short version of the program's code block of interest would look something like:

const readline = require('readline');
const filesystem = require('fs');

const reader = readline.createInterface(
 input: filesystem.createReadStream(pathToSomeCSV)
);

reader.on('line', async (line) => 
 await doSomeDBStuff();
)

If I leave the above the way it is, the process does not exit. However, if I

reader.on('close', () => process.exit());

then the process exits prior to all of the on('line') callbacks finishing and their promises resolving.

My question is: is there a way to say "Upon all lines being read AND all on('line') callbacks being completed with their promises resolved, then exit the process (I assume with process.exit())"?

node.js promise async-await

share|improve this question

asked Mar 7 at 14:10

northsideknightnorthsideknight

8891720

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  Just drop the close handler. When all asynchronous work is done (and there are no outstanding handler), node.js will stop by itself. You don't need to call process.exit() explicitly, that's only useful for prematurely exiting (or exiting with a specific error code). You should investigate why your process does not end, is some db connection kept open?
  
  – Bergi
  Mar 7 at 14:15
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  so it is an open db connection pool that is causing the process not to exit. I still have the problem but it could be worded differently because it is a problem with db library (sequelize) not readline.
  
  – northsideknight
  Mar 7 at 15:28
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Yeah. Is there a method that drains sequelizes connection pool? You could call that in the close handler.
  
  – Bergi
  Mar 7 at 15:44
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  I could not find one. What we ended up doing was, for every operation that needs to occur asynchronously, we added a promise to an array that would resolve when that operation completed. Then, upon close we used await Promise.all(operations), when that finished, we explicitly closed the Sequelize connection pool.
  
  – northsideknight
  Mar 8 at 14:14
  

  
  
  
  

add a comment | 

I have a Node v10.14.1 program that reads a CSV file line-by-line using the readline Interface

My .on('line') is an async callback performs some operations which read/write from a db, thus I use async/await to deal with the promises.

A short version of the program's code block of interest would look something like:

const readline = require('readline');
const filesystem = require('fs');

const reader = readline.createInterface(
 input: filesystem.createReadStream(pathToSomeCSV)
);

reader.on('line', async (line) => 
 await doSomeDBStuff();
)

If I leave the above the way it is, the process does not exit. However, if I

reader.on('close', () => process.exit());

then the process exits prior to all of the on('line') callbacks finishing and their promises resolving.

My question is: is there a way to say "Upon all lines being read AND all on('line') callbacks being completed with their promises resolved, then exit the process (I assume with process.exit())"?

node.js promise async-await

share|improve this question

asked Mar 7 at 14:10

northsideknightnorthsideknight

8891720

const readline = require('readline');
const filesystem = require('fs');

const reader = readline.createInterface(
 input: filesystem.createReadStream(pathToSomeCSV)
);

reader.on('line', async (line) => 
 await doSomeDBStuff();
)

reader.on('close', () => process.exit());

share|improve this question

asked Mar 7 at 14:10

northsideknightnorthsideknight

8891720

share|improve this question

asked Mar 7 at 14:10

northsideknightnorthsideknight

8891720

asked Mar 7 at 14:10

northsideknightnorthsideknight

8891720

asked Mar 7 at 14:10

northsideknightnorthsideknight

8891720