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reusify

Reuse your objects and functions for maximum speed. This technique will make any function run ~10% faster. You call your functions a lot, and it adds up quickly in hot code paths.

$ node benchmarks/createNoCodeFunction.js
Total time 53133
Total iterations 100000000
Iteration/s 1882069.5236482036
$ node benchmarks/reuseNoCodeFunction.js
Total time 50617
Total iterations 100000000
Iteration/s 1975620.838848608

The above benchmark uses fibonacci to simulate a real high-cpu load. The actual numbers might differ for your use case, but the difference should not.

The benchmark was taken using Node v6.10.0.

This library was extracted from fastparallel.

# Example

var reusify = require('reusify')
var fib = require('reusify/benchmarks/fib')
var instance = reusify(MyObject)
// get an object from the cache,
// or creates a new one when cache is empty
var obj = instance.get()
// set the state
obj.num = 100
obj.func()
// reset the state.
// if the state contains any external object
// do not use delete operator (it is slow)
// prefer set them to null
obj.num = 0
// store an object in the cache
instance.release(obj)
function MyObject () {
// you need to define this property
// so V8 can compile MyObject into an
// hidden class
this.next = null
this.num = 0
var that = this
// this function is never reallocated,
// so it can be optimized by V8
this.func = function () {
if (null) {
// do nothing
} else {
// calculates fibonacci
fib(that.num)
}
}
}

The above example was intended for synchronous code, let's see async:

var reusify = require('reusify')
var instance = reusify(MyObject)
for (var i = 0; i < 100; i++) {
getData(i, console.log)
}
function getData (value, cb) {
var obj = instance.get()
obj.value = value
obj.cb = cb
obj.run()
}
function MyObject () {
this.next = null
this.value = null
var that = this
this.run = function () {
asyncOperation(that.value, that.handle)
}
this.handle = function (err, result) {
that.cb(err, result)
that.value = null
that.cb = null
instance.release(that)
}
}

Also note how in the above examples, the code, that consumes an istance of `MyObject`, reset the state to initial condition, just before storing it in the cache. That's needed so that every subsequent request for an instance from the cache, could get a clean instance.

# Why

It is faster because V8 doesn't have to collect all the functions you create. On a short-lived benchmark, it is as fast as creating the nested function, but on a longer time frame it creates less pressure on the garbage collector.

# Other examples

If you want to see some complex example, checkout middie and steed.

# Acknowledgements

Thanks to Trevor Norris for getting me down the rabbit hole of performance, and thanks to Mathias Buss for suggesting me to share this trick.

# License

MIT