From dcedf1bab5e4dd15186446f794b91a6cf6bfe669 Mon Sep 17 00:00:00 2001
From: blam <ben@blam.sh>
Date: Mon, 3 Oct 2022 15:15:23 +0200
Subject: [PATCH] chore: store the promise instead to combat race conditions

Signed-off-by: blam <ben@blam.sh>
---
 .../src/database/DatabaseManager.test.ts      |  7 +-
 .../src/database/DatabaseManager.ts           | 77 +++++++++++--------
 2 files changed, 49 insertions(+), 35 deletions(-)

diff --git a/packages/backend-common/src/database/DatabaseManager.test.ts b/packages/backend-common/src/database/DatabaseManager.test.ts
index 8ecb5e4ffb..95511d5aba 100644
--- a/packages/backend-common/src/database/DatabaseManager.test.ts
+++ b/packages/backend-common/src/database/DatabaseManager.test.ts
@@ -345,9 +345,10 @@ describe('DatabaseManager', () => {
     });
 
     it('returns the same client for the same pluginId', async () => {
-      const client1 = await manager.forPlugin('plugin1').getClient();
-      const client2 = await manager.forPlugin('plugin1').getClient();
-
+      const [client1, client2] = await Promise.all([
+        manager.forPlugin('plugin1').getClient(),
+        manager.forPlugin('plugin1').getClient(),
+      ]);
       expect(mocked(createDatabaseClient)).toHaveBeenCalledTimes(1);
 
       expect(client1).toBe(client2);
diff --git a/packages/backend-common/src/database/DatabaseManager.ts b/packages/backend-common/src/database/DatabaseManager.ts
index 4a677a48a7..a58799a724 100644
--- a/packages/backend-common/src/database/DatabaseManager.ts
+++ b/packages/backend-common/src/database/DatabaseManager.ts
@@ -84,7 +84,7 @@ export class DatabaseManager {
     private readonly config: Config,
     private readonly prefix: string = 'backstage_plugin_',
     private readonly options?: DatabaseManagerOptions,
-    private readonly databaseCache: Map<string, Knex> = new Map(),
+    private readonly databaseCache: Map<string, Promise<Knex>> = new Map(),
   ) {}
 
   /**
@@ -311,45 +311,58 @@ export class DatabaseManager {
     if (this.databaseCache.has(pluginId)) {
       return this.databaseCache.get(pluginId)!;
     }
-    const pluginConfig = new ConfigReader(
-      this.getConfigForPlugin(pluginId) as JsonObject,
-    );
 
-    const databaseName = this.getDatabaseName(pluginId);
-    if (databaseName && this.getEnsureExistsConfig(pluginId)) {
+    const clientPromise = new Promise<Knex>(async (resolve, reject) => {
       try {
-        await ensureDatabaseExists(pluginConfig, databaseName);
-      } catch (error) {
-        throw new Error(
-          `Failed to connect to the database to make sure that '${databaseName}' exists, ${error}`,
+        const pluginConfig = new ConfigReader(
+          this.getConfigForPlugin(pluginId) as JsonObject,
         );
-      }
-    }
 
-    let schemaOverrides;
-    if (this.getPluginDivisionModeConfig() === 'schema') {
-      schemaOverrides = this.getSchemaOverrides(pluginId);
-      if (this.getEnsureExistsConfig(pluginId)) {
-        try {
-          await ensureSchemaExists(pluginConfig, pluginId);
-        } catch (error) {
-          throw new Error(
-            `Failed to connect to the database to make sure that schema for plugin '${pluginId}' exists, ${error}`,
-          );
+        const databaseName = this.getDatabaseName(pluginId);
+        if (databaseName && this.getEnsureExistsConfig(pluginId)) {
+          try {
+            await ensureDatabaseExists(pluginConfig, databaseName);
+          } catch (error) {
+            throw new Error(
+              `Failed to connect to the database to make sure that '${databaseName}' exists, ${error}`,
+            );
+          }
         }
+
+        let schemaOverrides;
+        if (this.getPluginDivisionModeConfig() === 'schema') {
+          schemaOverrides = this.getSchemaOverrides(pluginId);
+          if (this.getEnsureExistsConfig(pluginId)) {
+            try {
+              await ensureSchemaExists(pluginConfig, pluginId);
+            } catch (error) {
+              throw new Error(
+                `Failed to connect to the database to make sure that schema for plugin '${pluginId}' exists, ${error}`,
+              );
+            }
+          }
+        }
+
+        const databaseClientOverrides = mergeDatabaseConfig(
+          {},
+          this.getDatabaseOverrides(pluginId),
+          schemaOverrides,
+        );
+
+        const client = createDatabaseClient(
+          pluginConfig,
+          databaseClientOverrides,
+        );
+        this.startKeepaliveLoop(pluginId, client);
+        resolve(client);
+      } catch (e) {
+        reject(e);
       }
-    }
+    });
 
-    const databaseClientOverrides = mergeDatabaseConfig(
-      {},
-      this.getDatabaseOverrides(pluginId),
-      schemaOverrides,
-    );
+    this.databaseCache.set(pluginId, clientPromise);
 
-    const client = createDatabaseClient(pluginConfig, databaseClientOverrides);
-    this.startKeepaliveLoop(pluginId, client);
-    this.databaseCache.set(pluginId, client);
-    return client;
+    return clientPromise;
   }
 
   private startKeepaliveLoop(pluginId: string, client: Knex): void {