Bug Fix: infinite Loop

[willianmarquess]

Hi, there is an infinite loop bug that occurs in the bgThreadFunc() method:
I encountered this issue while analyzing a problem in a production environment where pods were freezing and restarting, this issue only occurs in services that handle high volumes of message processing via queues.

Mode: Thin

Problem:

When we configure a low number of connections in the pool (1, 4, 8, etc.) and the application experiences high concurrency (queue/event processing), it enters an infinite loop due to this part of code:
pool.js

async bgThreadFunc() {
    while (!this._poolCloseWaiter) {
      const numToCreate = this._getNumConnsToCreate(); //when here returns 0
      
      for (let i = 0; i < numToCreate; i++) {
        ...
      }

      // and here has this._pendingRequests.length > 0
      //then we have an infinite loop
      if ((this._pendingRequests.length == 0 || this._bgErr) &&
        this.getConnectionsOpen() >= this._poolMin) {
        await new Promise((resolve) => {
          this.bgWaiter = resolve;
        });
        this.bgWaiter = null;
      }
      ...
    }
  }

How to reproduce:

This scenario only occurs in situations of high concurrency; I’ll leave an example here for you to reproduce the problem.
(this code is only trying to simulate an queue/event concurrent processing)

'use strict';
const oracledb = require('oracledb');
const EventEmitter = require('events');
oracledb.outFormat = oracledb.OUT_FORMAT_OBJECT;
const {
    DB_USER = 'your_user',
    DB_PASSWORD = 'your_pass',
    DB_CONNECT_STRING = 'your_connection_string',
} = process.env;
class Broker extends EventEmitter { }
let pool;
async function createTableIfNotExists(connection) {
  const plsql = `
    BEGIN
      EXECUTE IMMEDIATE '
        CREATE TABLE accounts (
          id            NUMBER PRIMARY KEY,
          balance       NUMBER NOT NULL,
          updated_at    TIMESTAMP DEFAULT SYSTIMESTAMP,
          version       NUMBER DEFAULT 0
        )
      ';
    EXCEPTION
      WHEN OTHERS THEN
        IF SQLCODE != -955 THEN
          RAISE;
        END IF;
    END;
  `;
  await connection.execute(plsql);
}

async function processMessage(id) {
    let connection;
    try {
        connection = await pool.getConnection();
        await connection.execute(
            `   UPDATE accounts
                SET balance = balance + :delta,
                    version = version + 1
                WHERE id = :id
                `,
            { delta: 10, id: 1 }
        );
    } catch (err) {
        console.error(`[${id}] error:`, err.message);
    } finally {
        if (connection) {
            try {
                await connection.close();
                console.log(`[${id}] connection released`);
            } catch (error) {
                console.error(`[${id}] error when trying to close connection:`, error.message);
            }
        }
    }
}

async function main() {
    const broker = new Broker();
    broker.on('message', (id) => {
        processMessage(id);
    });
    pool = await oracledb.createPool({
        user: DB_USER,
        password: DB_PASSWORD,
        connectString: DB_CONNECT_STRING,
        poolMin: 4,
        poolMax: 4,
        queueMax: 100000,
        poolIncrement: 1,
        enableStatistics: true,
    });
    await createTableIfNotExists(await pool.getConnection());
    setInterval(() => {
        console.log(JSON.stringify(pool.getStatistics()));
    }, 1000);
    setInterval(() => {
        for (let j = 0; j < 5; j++) {
            broker.emit('message', j);
        }
    }, 2);
}
main().catch(console.error);

Solution:

I left a suggested three-part solution in the code:

1 - In bgThreadFunc, check only for cases where numToCreate <= 0 to perform the await and avoid entering sync infinite loop.
2 - When calling release(), check for any pending tasks and attempt to reuse and resolve them immediately.
3 - When there is a pending task, we must wake up bgWaiter().

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[sharadraju]

@willianmarquess Thank you for bringing this to our attention and the detailed analysis.

Please note that we will evaluate the PR and then include the code changes from our end in an upcoming release (while giving you the due credit in the release notes :) ), based on our analysis and testing.

We would also request you to sign the OCA agreement.

To sign the OCA, please create an Oracle account and sign the OCA in Oracle's Contributor Agreement Application

[willianmarquess]

@willianmarquess Thank you for bringing this to our attention and the detailed analysis.

Please note that we will evaluate the PR and then include the code changes from our end in an upcoming release (while giving you the due credit in the release notes :) ), based on our analysis and testing.

We would also request you to sign the OCA agreement.

To sign the OCA, please create an Oracle account and sign the OCA in Oracle's Contributor Agreement Application

I am trying to sign, but I am encountering an error when trying to download the OCA document (I am from Brazil).