如何设置两个使用相同内存持久化存储的核心数据堆栈？

需要在代码中使用多个NSPersistentStoreCoordinator对象和NSManagedObjectModel对象，但使用相同的NSPersistentStore对象来进行两个堆栈之间的通信。

首先，我们需要创建一个NSManagedObjectModel对象：

let model = NSManagedObjectModel.mergedModel(from: nil)!

接下来，我们需要创建两个不同的NSPersistentStoreCoordinator对象：

let coordinator1 = NSPersistentStoreCoordinator(managedObjectModel: model)
let coordinator2 = NSPersistentStoreCoordinator(managedObjectModel: model)

接下来，我们需要创建两个不同的核心数据堆栈，并将它们分别与不同的NSPersistentStoreCoordinator对象关联：

let stack1 = CoreDataStack(persistentStoreCoordinator: coordinator1)
let stack2 = CoreDataStack(persistentStoreCoordinator: coordinator2)

在我们的CoreDataStack类中，我们需要实现persistentStoreCoordinator属性来返回我们传递给初始化程序的NSPersistentStoreCoordinator对象：

class CoreDataStack {
    let persistentStoreCoordinator: NSPersistentStoreCoordinator

    init(persistentStoreCoordinator: NSPersistentStoreCoordinator) {
        self.persistentStoreCoordinator = persistentStoreCoordinator
    }

    // ...

    lazy var persistentContainer: NSPersistentContainer = {
        let container = NSPersistentContainer(name: "MyModelName")
        container.persistentStoreDescriptions = [NSPersistentStoreDescription()]
        container.persistentStoreDescriptions.first!.type = NSInMemoryStoreType
        container.persistentStoreDescriptions.first!.configuration = "Default"
        container.persistentStoreDescriptions.first!.shouldAddStoreAsynchronously = false
        container.persistentStoreDescriptions.first!.shouldMigrateStoreAutomatically = true
        container.persistentStoreDescriptions.first!.shouldInferMappingModelAutomatically = true
        container.loadPersistentStores(completionHandler: { (_, error) in
            if let error = error as NSError? {
                fatalError("Unresolved error \(error), \(error.userInfo)")
            }
        })
        return container
    }()
}

注意，我们将每个堆栈的persistentStoreDescriptions设置为相同。这使得两个堆栈使用相同的