The issue with app companies
Vapor has a factor known as companies, you may add new performance to the system by following the sample described within the documentation. Learn-only companies are nice there isn’t any problem with them, they all the time return a brand new occasion of a given object that you just wish to entry.
The issue is once you wish to entry a shared object or in different phrases, you wish to outline a writable service. In my case I wished to create a shared cache dictionary that I may 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 every part 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 appears good and it will work and you’re proper, it really works, however there’s a HUGE drawback with this resolution. It isn’t thread-safe in any respect. ??
Whenever you open the browser and sort http://localhost:8080/ the web page will load, however once 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 problem on GitHub, which describes the very same drawback. 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 capable of 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 bought very annoyed.
Constructing a customized international storage
After a break this problem was nonetheless bugging my thoughts, so I’ve determined to do some extra analysis. Vapor’s discord server is often an ideal place to get the correct solutions.
I’ve additionally regarded up different net frameworks, and I used to be fairly shocked that Hummingbird provides an EventLoopStorage by default. Anyway, I am not going to modify, however nonetheless it is a good to have characteristic.
As I used to be wanting on the solutions I noticed that I would like 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 solution to return the values primarily based on the keys. When 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 non-public Cache class that can maintain our tips to the situations. 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 {
remaining 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 give you this resolution. Perhaps it is nonetheless not one of the best ways to deal with this problem, however it 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 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 = 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 assessments 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 one of the best ways to deal with my drawback 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 remedy 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, 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, however it’s nice to see that lastly we’re going to have the ability to do away with EventLoopFutures. ?