Memory cache client should share memory.

Signed-off-by: Eric Peterson <ericpeterson@spotify.com>

.changeset/dar-jag-gar.md

@@ -0,0 +1,5 @@
+---
+'@backstage/backend-common': patch
+---
+
+In-memory cache clients instantiated from the same cache manager now share the same memory space.

packages/backend-common/src/cache/CacheManager.test.ts

@@ -147,6 +147,22 @@ describe('CacheManager', () => {
       });
     });
 
+    it('shares memory across multiple instances of the memory client', () => {
+      const manager = CacheManager.fromConfig(defaultConfig());
+      const plugin = 'test-plugin';
+
+      // Instantiate two in-memory clients.
+      manager.forPlugin(plugin).getClient({ defaultTtl: 10 });
+      manager.forPlugin(plugin).getClient({ defaultTtl: 10 });
+
+      const cache = Keyv as unknown as jest.Mock;
+      const mockCall2 = cache.mock.calls.splice(-1)[0][0];
+      const mockCall1 = cache.mock.calls.splice(-1)[0][0];
+
+      // Note: .toBe() checks referential identity of object instances.
+      expect(mockCall1.store).toBe(mockCall2.store);
+    });
+
     it('returns a memcache client when configured', () => {
       const expectedHost = '127.0.0.1:11211';
       const manager = CacheManager.fromConfig(

packages/backend-common/src/cache/CacheManager.ts

@@ -42,6 +42,13 @@ export class CacheManager {
     none: this.getNoneClient,
   };
 
+  /**
+   * Shared memory store for the in-memory cache client. Sharing the same Map
+   * instance ensures get/set/delete operations hit the same store, regardless
+   * of where/when a client is instantiated.
+   */
+  private readonly memoryStore = new Map();
+
   private readonly logger: Logger;
   private readonly store: keyof CacheManager['storeFactories'];
   private readonly connection: string;
@@ -133,6 +140,7 @@ export class CacheManager {
     return new Keyv({
       namespace: pluginId,
       ttl: defaultTtl,
+      store: this.memoryStore,
     });
   }