test: deadlock if in-use connections not closed

Author: nbbeeken

test/integration/node-specific/mongo_client.test.ts

@@ -12,13 +12,14 @@ import {
   Db,
   getTopology,
   MongoClient,
+  MongoClientClosedError,
   MongoNotConnectedError,
   MongoServerSelectionError,
   ReadPreference,
   ServerDescription,
   Topology
 } from '../../mongodb';
-import { runLater } from '../../tools/utils';
+import { clearFailPoint, configureFailPoint, runLater } from '../../tools/utils';
 import { setupDatabase } from '../shared';
 
 describe('class MongoClient', function () {
@@ -1064,6 +1065,51 @@ describe('class MongoClient', function () {
         expect(client.s.activeCursors).to.have.lengthOf(1);
       });
     });
+
+    describe('maxPoolSize is not fully used when running clean up operations', function () {
+      let client;
+
+      beforeEach(async function () {
+        await configureFailPoint(this.configuration, {
+          configureFailPoint: 'failCommand',
+          mode: 'alwaysOn',
+          data: {
+            failCommands: ['insert'],
+            blockConnection: true,
+            blockTimeMS: 500
+          }
+        });
+
+        client = this.configuration.newClient({}, { maxPoolSize: 1, monitorCommands: true });
+      });
+
+      afterEach(async function () {
+        await clearFailPoint(this.configuration);
+        await client.close();
+      });
+
+      it(
+        'closes in-use connections before running clean up operations avoiding a deadlock',
+        { requires: { topology: '!load-balanced' } },
+        async () => {
+          const inserted = client
+            .db('t')
+            .collection('t')
+            .insertOne({ a: 1 })
+            .catch(error => error);
+
+          await once(client, 'commandStarted');
+
+          const start = performance.now();
+          await client.close();
+          const error = await inserted;
+          const end = performance.now();
+
+          expect(end - start).to.be.lessThan(100);
+          expect(error).to.be.instanceOf(MongoClientClosedError);
+        }
+      );
+    });
   });
 
   context('when connecting', function () {