The issue with app companies
Vapor has a factor referred to as companies, you may add new performance to the system by following the sample described within the documentation. Learn-only companies are nice there is no such thing as a challenge with them, they all the time return a brand new occasion of a given object that you just need to entry.
The issue is if you need to entry a shared object or in different phrases, you need to outline a writable service. In my case I needed to create a shared cache dictionary that I might use to retailer some preloaded variables from the database.
My preliminary try was to create a writable service that I can use to retailer these key-value pairs. I additionally needed to make use of a middleware and cargo every little thing there upfront, earlier than the route handlers. 💡
import Vapor
personal extension Utility {
struct VariablesStorageKey: StorageKey {
typealias Worth = [String: String]
}
var variables: [String: String] {
get {
self.storage[VariablesStorageKey.self] ?? [:]
}
set {
self.storage[VariablesStorageKey.self] = newValue
}
}
}
public extension Request {
func variable(_ key: String) -> String? {
utility.variables[key]
}
}
struct CommonVariablesMiddleware: AsyncMiddleware {
func reply(to req: Request, chainingTo subsequent: AsyncResponder) async throws -> Response {
let variables = attempt await CommonVariableModel.question(on: req.db).all()
var tmp: [String: String] = [:]
for variable in variables {
if let worth = variable.worth {
tmp[variable.key] = worth
}
}
req.utility.variables = tmp
return attempt await subsequent.reply(to: req)
}
}Now you may suppose that hey this seems to be good and it will work and you might be proper, it really works, however there’s a HUGE downside with this resolution. It is not thread-safe in any respect. ⚠️
While you open the browser and sort http://localhost:8080/ the web page will load, however if you begin bombarding the server with a number of requests utilizing a number of threads (wrk -t12 -c400 -d30s http://127.0.0.1:8080/) the appliance will merely crash.
There’s a related challenge on GitHub, which describes the very same downside. Sadly I used to be unable to resolve this with locks, I do not know why nevertheless it tousled much more issues with unusual errors and since I am additionally not in a position to run devices on my M1 Mac Mini, as a result of Swift packages are usually not code signed by default. I’ve spent so many hours on this and I’ve acquired very annoyed.
Constructing a customized international storage
After a break this challenge was nonetheless bugging my thoughts, so I’ve determined to do some extra analysis. Vapor’s discord server is often an awesome place to get the suitable solutions.
I’ve additionally appeared up different net frameworks, and I used to be fairly shocked that Hummingbird gives an EventLoopStorage by default. Anyway, I am not going to change, however nonetheless it is a good to have function.
As I used to be wanting on the solutions I spotted that I want one thing much like the req.auth property, so I’ve began to research the implementation particulars extra carefully.
First, I eliminated the protocols, as a result of I solely wanted a plain [String: Any] dictionary and a generic method to return the values primarily based on the keys. In case you take a more in-depth look it is fairly a easy design sample. There’s a helper struct that shops the reference of the request and this struct has an personal Cache class that may maintain our tips that could the cases. The cache is obtainable by way of a property and it’s saved contained in the req.storage.
import Vapor
public extension Request {
var globals: Globals {
return .init(self)
}
struct Globals {
let req: Request
init(_ req: Request) {
self.req = req
}
}
}
public extension Request.Globals {
func get<T>(_ key: String) -> T? {
cache[key]
}
func has(_ key: String) -> Bool {
get(key) != nil
}
func set<T>(_ key: String, worth: T) {
cache[key] = worth
}
func unset(_ key: String) {
cache.unset(key)
}
}
personal extension Request.Globals {
ultimate class Cache {
personal var storage: [String: Any]
init() {
self.storage = [:]
}
subscript<T>(_ sort: String) -> T? {
get { storage[type] as? T }
set { storage[type] = newValue }
}
func unset(_ key: String) {
storage.removeValue(forKey: key)
}
}
struct CacheKey: StorageKey {
typealias Worth = Cache
}
var cache: Cache {
get {
if let current = req.storage[CacheKey.self] {
return current
}
let new = Cache()
req.storage[CacheKey.self] = new
return new
}
set {
req.storage[CacheKey.self] = newValue
}
}
}After altering the unique code I’ve provide you with this resolution. Possibly it is nonetheless not one of the best ways to deal with this challenge, nevertheless it works. I used to be in a position to retailer my variables inside a worldwide storage with out crashes or leaks. The req.globals storage property goes to be shared and it makes doable to retailer knowledge that must be loaded asynchronously. 😅
import Vapor
public extension Request {
func variable(_ key: String) -> String? {
globals.get(key)
}
}
struct CommonVariablesMiddleware: AsyncMiddleware {
func reply(to req: Request, chainingTo subsequent: AsyncResponder) async throws -> Response {
let variables = attempt await CommonVariableModel.question(on: req.db).all()
for variable in variables {
if let worth = variable.worth {
req.globals.set(variable.key, worth: worth)
}
else {
req.globals.unset(variable.key)
}
}
return attempt await subsequent.reply(to: req)
}
}After I’ve run a number of extra assessments utilizing wrk I used to be in a position to affirm that the answer works. I had no points with threads and the app had no reminiscence leaks. It was a aid, however nonetheless I am undecided if that is one of the best ways to deal with my downside or not. Anyway I needed to share this with you as a result of I consider that there’s not sufficient details about thread security.
The introduction of async / await in Vapor will resolve many concurrency issues, however we’ll have some new ones as effectively. I actually hope that Vapor 5 will probably be an enormous enchancment over v4, persons are already throwing in concepts and they’re having discussions about the way forward for Vapor on discord. That is just the start of the async / await period each for Swift and Vapor, nevertheless it’s nice to see that lastly we’re going to have the ability to do away with EventLoopFutures. 🥳