The issue with app providers
Vapor has a factor referred to as providers, you’ll be able to add new performance to the system by following the sample described within the documentation. Learn-only providers are nice there isn’t a difficulty with them, they at all times return a brand new occasion of a given object that you simply 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 wished 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 wished to make use of a middleware and cargo all the things there upfront, earlier than the route handlers. 💡
import Vapor
non-public extension Software {
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? {
software.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.software.variables = tmp
return attempt await subsequent.reply(to: req)
}
}
Now you may assume that hey this appears good and it will work and you’re proper, it really works, however there’s a HUGE downside with this answer. 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 applying will merely crash.
There’s a comparable difficulty on GitHub, which describes the very same downside. Sadly I used to be unable to resolve this with locks, I do not know why however 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 obtained very pissed off.
Constructing a customized international storage
After a break this difficulty was nonetheless bugging my thoughts, so I’ve determined to do some extra analysis. Vapor’s discord server is normally an amazing place to get the precise solutions.
I’ve additionally seemed up different net frameworks, and I used to be fairly stunned that Hummingbird gives an EventLoopStorage by default. Anyway, I am not going to modify, however nonetheless it is a good to have function.
As I used to be trying on the solutions I noticed that I want one thing much like the req.auth property, so I’ve began to analyze 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 solution to return the values based mostly on the keys. In the event you take a better 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 non-public Cache class that can maintain our tips that could the situations. The cache is out there 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)
}
}
non-public extension Request.Globals {
remaining class Cache {
non-public 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 answer. Possibly it is nonetheless not one of the simplest ways to deal with this difficulty, however 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 attainable to retailer information 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 verify that the answer works. I had no points with threads and the app had no reminiscence leaks. It was a reduction, however nonetheless I am undecided if that is one of the simplest ways to deal with my downside or not. Anyway I wished 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 properly. I actually hope that Vapor 5 can be an enormous enchancment over v4, individuals 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, however it’s nice to see that lastly we’re going to have the ability to eliminate EventLoopFutures. 🥳
