Singleton services #4
Description
Is your feature request related to a problem? Please describe.
I have a service that manages the configuration data for my application. This configuration data is loaded from a file when the service is created, and is saved whenever a value is changed. These changes can be sent to the service from any other service/actor, but only one instance of the ConfigService should ever exist because it holds a handle to the config file and multiple instances would override each others' changes and potentially lose config data.
I've used ServiceConcurrency::None to have only a single instance of the service, but it still requires that the data is wrapped in a Mutex. It's possible to make a singleton this way, but not very convenient/user-friendly for something where I should be able to assume concurrent access will not happen (because messages are processed one by one).
Describe the solution you'd like
A Singleton trait, similar to Service, that guarantees only a single instance of the service exists, that doesn't require me to use a Mutex for its state, and that uses &mut self for its Listen & Serve traits.
Example (pseudocode):
struct ConfigService {
file_handle: File,
}
impl Singleton for ConfigService {
async fn initialize(system) -> Self {
ConfigService {
file: File::Open().await,
}
}
}
struct SetConfig(String);
impl Listen<SetConfig> for ConfigService {
async fn handle(&mut self, data: SetConfig) {
self.file.write_all(data.0).await;
}
}