The issue with app companies
Vapor has a factor referred to as companies, you possibly can 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 subject with them, they all the time 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 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 thing 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 = strive 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 strive await subsequent.reply(to: req)
}
}
Now you may assume that hey this seems to be good and it will work and you might be proper, it really works, however there’s a HUGE drawback with this answer. It is not thread-safe in any respect. ⚠️
While you open the browser and kind 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 subject on GitHub, which describes the very same drawback. Sadly I used to be unable to unravel this with locks, I do not know why but it surely tousled much more issues with unusual errors and since I am additionally not capable of run devices on my M1 Mac Mini, as a result of Swift packages should not code signed by default. I’ve spent so many hours on this and I’ve bought very annoyed.
Constructing a customized world storage
After a break this subject was nonetheless bugging my thoughts, so I’ve determined to do some extra analysis. Vapor’s discord server is often an amazing place to get the correct solutions.
I’ve additionally regarded up different internet frameworks, and I used to be fairly stunned that Hummingbird affords 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 trying on the options I noticed that I would like 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 strategy to return the values based mostly on the keys. If you happen to 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 non-public Cache class that can maintain our tips to the cases. The cache is on the market by means 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 {
last class Cache {
non-public var storage: [String: Any]
init() {
self.storage = [:]
}
subscript<T>(_ kind: 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 the easiest way to deal with this subject, but it surely works. I used to be capable of retailer my variables inside a world 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 = strive 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 strive await subsequent.reply(to: req)
}
}
After I’ve run a number of extra checks utilizing wrk I used to be capable of 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 the easiest way to deal with my drawback 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 clear up many concurrency issues, however we will have some new ones as properly. I actually hope that Vapor 5 will probably 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 only the start of the async / await period each for Swift and Vapor, but it surely’s nice to see that lastly we’re going to have the ability to do away with EventLoopFutures. 🥳
