Implement autosaving of data held in memory

Add controller.autosave_interval config that specifies the frequency
which controller config, hosts, instances, users, mod packs and plugin
specific data which is held in memory should be automatically flushed to
disk if they have changed since the last time they were saved.  This
prevents data loss in the event of a server crash.

Plugins can use the onSaveData hook to save its own data at the same
time as the controller does and this obsoletes making an autosave
interval in the plugin.

Resolves #523.

plugins/subspace_storage/controller.ts

@@ -75,9 +75,9 @@ export class ControllerPlugin extends BaseControllerPlugin {
 	itemUpdateRateLimiter!: lib.RateLimiter;
 	itemsLastUpdate!: Map<string, number>;
 	subscribedControlLinks!: Set<ControlConnection>;
-	autosaveId!: ReturnType<typeof setInterval>;
 	doleMagicId!: ReturnType<typeof setInterval>;
 	neuralDole!: dole.NeuralDole;
+	storageDirty = false;
 
 	async init() {
 		this.items = await loadDatabase(this.controller.config, this.logger);
@@ -92,11 +92,6 @@ export class ControllerPlugin extends BaseControllerPlugin {
 			},
 		});
 		this.itemsLastUpdate = new Map(this.items.getEntries());
-		this.autosaveId = setInterval(() => {
-			saveDatabase(this.controller.config, this.items, this.logger).catch(err => {
-				this.logger.error(`Unexpected error autosaving items:\n${err.stack}`);
-			});
-		}, this.controller.config.get("subspace_storage.autosave_interval") as number * 1000);
 
 		this.neuralDole = new dole.NeuralDole({ items: this.items });
 		this.doleMagicId = setInterval(() => {
@@ -117,6 +112,7 @@ export class ControllerPlugin extends BaseControllerPlugin {
 
 	updateStorage() {
 		this.itemUpdateRateLimiter.activate();
+		this.storageDirty = true;
 	}
 
 	broadcastStorage() {
@@ -254,8 +250,13 @@ export class ControllerPlugin extends BaseControllerPlugin {
 
 	async onShutdown() {
 		this.itemUpdateRateLimiter.cancel();
-		clearInterval(this.autosaveId);
 		clearInterval(this.doleMagicId);
-		await saveDatabase(this.controller.config, this.items, this.logger);
+	}
+
+	async onSaveData() {
+		if (this.storageDirty) {
+			this.storageDirty = false;
+			await saveDatabase(this.controller.config, this.items, this.logger);
+		}
 	}
 }