Node.js script should wait before service is running

问题

I have a node.js script which starts at boot. It uses node-redis to create a client for Redis, but at boot Redis is not ready while node is already starting. So, it gives an exception and stops executing.

The first part looks like this:

var redis  = require("redis"),
    jobs   = require("jobs"),
    client = redis.createClient(),
    runner = new jobs(client, "job-queue",{});

// Continue using runner

The exception is thrown in line 3 (redis.createClient()).

My solution was to make an endless loop, create the client in a try/catch and when successful, stop the loop:

var redis  = require("redis"),
    jobs   = require("jobs"),
    queue  = 'job-queue',
    client = null,
    runner = null,
    createClient = function (redis, jobs, queue) {
        try {
            client = redis.createClient();
            return new jobs(client, queue, {});
        } catch (err) {
            return null;
        }
    };

while(true) {
    setTimeout(function() {
        runner = createClient(redis, jobs, queue);
    }, 1000);

    if (null !== runner) break;
}

// Continue using runner

After a couple of seconds, this is the output:

FATAL ERROR: JS Allocation failed - process out of memory

How can I solve this? I am searching for a solution which could be in php:

while (true) {
    $client = createClient($redis, $jobs, $queue);
    if ($client instanceof MyClient) break;
    else sleep(1);
}

回答1:

setTimeout is asynchronous. JavaScript (and Node.js) have very few functions that wait for something to happen before continuing (like sleep). Instead, execution continues to the next line right away, but you pass setTimeout a callback function which is run when it fires.

I would do something like this (warning, untested):

var redis  = require("redis"),
    jobs   = require("jobs"),
    queue  = 'job-queue';

function initializeRedis(callback) {
    (function createClient(){
        var runner;
        try {
            client = redis.createClient();
            runner = new jobs(client, queue, {});
        } catch (e) {}
        if (runner){
            callback(runner);
        } else {
            setTimeout(createClient, 1000);
        }
    })();
};

initializeRedis(function(runner){
    // Continue using runner
});

来源：https://stackoverflow.com/questions/7786660/node-js-script-should-wait-before-service-is-running

标签

javascript

node.js

settimeout