node.js never exits after insert to couchbase, opposite of most node questions

Question

My problem seems to be the opposite of every node.js question :-) I have a simple forEach loop to read a list of files and insert them into a Couchbase database. This works great, but it never exits after reading all the lines. So I added a counter to shutdown the couchbase connection after all inserts are complete. This works.

This process is intended to load hundreds of thousands of files, so I brought the async module into the mix to batch the inserts into groups of 100. The async.eachLimit is used to iterate over the array and insert documents in batches. Now the orig problem is back. Whatever magic async.eachLimit uses to recognize the process is complete is not happening.

I've been going through javascript scoping, callbacks, async, etc. Google searches are hitting keywords but not this issue. I've reduced the code down to the following testcase. To test, create three files and add their names to testlist.txt.

The async.eachLimit in place works up until it hits the limit, then hangs. Comment this out and uncomment array.forEach line and it works. Thanks in advance!

var fs = require('fs');
var couchbase = require('couchbase');
var async = require('async');

var filelist = 'testlist.txt';
var key_count = 0;
var cb_config = { host: 'localhost:8091', bucket: 'default'};
var db = new couchbase.Connection(cb_config, function(err) {
  if (err) {
    console.log('ERRR connect to couchbase at config['+cb_config+']');
    throw err;
  }
});

var insertFile=function(line) {
    console.log('LOAD ['+line+']');

    fs.readFile(line, function(file_err, f_doc) {
        if(file_err) throw file_err;

        db.set(line, f_doc, function(db_err, db_res){
            if (db_err) {
                console.log('FAIL ['+line+'] err['+db_err+']');
            } else {
                console.log('PASS ['+line+']');
            }

            key_count--;
            if (key_count == 0) {
                console.log('DONE Shutting down client, no more keys');
                db.shutdown();
            }
        });
    });
}

// read list of files into data array from file filelist
fs.readFile(filelist, function(filelist_err, lines) {
    if(filelist_err) throw filelist_err;

    // HACK split adds empty line to array, use replace to fix
    var array = lines.toString().replace(/\n$/, '').split('\n');
    key_count = array.length;
    console.log('INIT lines['+key_count+']');

    async.eachLimit(array, 2, insertFile, function(err) { console.log('FAIL async err['+err+']');} );
    //array.forEach(function(data){insertFile(data);return;});
});

Testcase output using array.forEach:

INIT lines[3]
LOAD [files.big.txt]
LOAD [files.little.txt]
LOAD [files.txt]
PASS [files.little.txt]
PASS [files.big.txt]
PASS [files.txt]
DONE Shutting down client, no more keys

Testcase output using async.eachLimit:

INIT lines[3]
LOAD [files.big.txt]
LOAD [files.little.txt]
PASS [files.little.txt]
PASS [files.big.txt]
... hang, never gets to 3...

Answer 1

After review with a coworker, they spotted my mistake. I missed the async callback in my insertFile function. Adding that in works and allows me to remove the key counter! Solution code below:

var fs = require('fs');
var couchbase = require('couchbase');
var async = require('async');

var filelist = 'testlist.txt';
var key_count = 0;
var cb_config = { host: 'localhost:8091', bucket: 'default'};
var db = new couchbase.Connection(cb_config, function(err) {
  if (err) {
    console.log('ERRR connect to couchbase at config['+cb_config+']');
    throw err;
  }
});

var insertFile=function(line, callback) {
    console.log('LOAD ['+line+']');

    fs.readFile(line, function(file_err, f_doc) {
        if(file_err) throw file_err;

        db.set(line, f_doc, function(db_err, db_res){
            if (db_err) {
                console.log('FAIL ['+line+'] err['+db_err+']');
                callback(db_err);
            } else {
                console.log('PASS ['+line+']');
                callback();
            }
        });
    });
}

// read list of files into data array from file filelist
fs.readFile(filelist, function(filelist_err, data) {
    if(filelist_err) throw filelist_err;

    // HACK stoopid bug split adds empty line to array, use replace to fix
    var array = data.toString().replace(/\n$/, '').split('\n');
    key_count = array.length;
    console.log('READ files['+key_count+']');

    async.eachLimit(array, 2, insertFile, function(err) { 
        if (err) console.log('LAST with async err['+err+']');

        console.log('DONE Shutting down client, no more keys');
        db.shutdown();
    });
});

And successful output:

$ node testcase.js
READ files[3]
LOAD [files.big.txt]
LOAD [files.little.txt]
PASS [files.little.txt]
LOAD [files.txt]
PASS [files.big.txt]
PASS [files.txt]
DONE Shutting down client, no more keys