Threads.md

Resolver: Threads

Thread Safety

Resolver uses a unique recursive locking strategy and is designed to be thread safe during service registration and resolution.

Successful service resolution assumes, however, that all service registrations will occur prior to the first resolution request.

If you kick off thread A to do registrations and then also kick off a thread B that needs to resolve some of those services... well, let's just say that bad things will probably occur as you're setting up a race between registrations and resolutions. It's hard, after all, to resolve a request for XYZService if the factory for that service has yet to be registered.

Fortunately, Resolver has a solution for that.

ResolverRegistering

If you use ResolverRegistering.registerAllServices to register all of your dependencies, then you shouldn't have any issues.

import Resolver

extension Resolver: ResolverRegistering {
    public static func registerAllServices() {
        registerMyNetworkServices()
        registerMyViewModels()
    }
    
    public static func registerMyNetworkServices() {
        register { ServiceA() }
        register { ServiceB() }
    }
    
    public static func registerMyViewModels() {
        register { ModelA() }
        register { ModelB() }
    }
}

Resolver will automatically call registerAllServices the very first time it's asked to resolve a particular service, ensuring that everything is properly registered before it goes looking for it.

For more, see the section on Registration.