I have a situation like:
function smth(data) {
// save data to db.
Object.findOne({ _id: ceva['id']}, function(obj) {
obj.save();
});
}
This function is called from various async calls. There is a race condition where the second findOne call runs before a previous save() runs.
Is there a way to work around this? Maybe using the async library to run things in series?
You can make use one of async control flows to ensure every iteration of smth() happens in order.
If you're not in favor of using a flow control library, you can easily achieve series execution of each event. Consider following code snippet:
function smth(data, cb) {
// save data to db.
findOne({
id: data.id
}, function (err, obj) {
if (!err && obj) {
savedb(obj, cb);
} else {
cb(err);
}
});
}
function findOne(filter, cb) {
// simulate find
setTimeout(function () {
cb(null, {
id: filter.id,
name: 'test',
role: 'test'
});
}, 500);
}
function savedb(obj, cb) {
//simulate db save
setTimeout(function () {
cb(null, obj);
}, 500);
}
// iterations count
var count = parseInt(process.argv[2], 10) || 3;
(function iterate(i) {
console.log(i);
if (i === count) {
// iterations complete
process.exit(1);
}
var data = {
id: 123 + i
};
smth(data, function (err, res) {
console.log(err || res);
iterate(++i);
});
})(0);
smth() getting called, multiple times in a loop or from multiple places? If it's a loop, above routine or async.series, async.waterfall or async.compose() can be made to work. If it's being triggered from multiple places, you will need to implement a task queue, use async.queue or any task queue impl will do. async explains these tasks w/ examples, can you try them and see if they work for you?//make this follow async conventions with callback argument last
function smth(data, callback) {
//pseudocode database API here
db.save(data, function (error) {
if (error) {
callback(error);
return;
}
Object.findOne({ _id: ceva['id']}, function(obj) {
obj.save(callback);
});
});
}
That's the basic callback approach. You can use async.js if you like to clean it up a bit or study callbackhell.com for more ways to avoid the nested functions.
