Murlock NPM | npm.io

NestJS MurLock

MurLock is a distributed lock solution designed for the NestJS framework. It provides a decorator @MurLock() that allows for critical sections of your application to be locked to prevent race conditions. MurLock uses Redis to ensure locks are respected across multiple instances of your application, making it perfect for microservices.

Features

Redis-Based: Implements a fast and effective lock mechanism using Redis.
Parameter-Based Locking: Creates locks based on request parameters or bodies.
Highly Customizable: Customize many parameters, such as lock duration.
Retry Mechanism: Implements an exponential back-off strategy if the lock is not obtained.
Logging: Provides: logging options for debugging and monitoring.
OOP and Generic Structure: Easily integratable and expandable due to its OOP and generic design.

Installation

MurLock has a peer dependency on @nestjs/common and reflect-metadata. These should already be installed in your NestJS project. In addition, you'll also need to install the redis package.

npm install --save murlock redis reflect-metadata

Basic Usage

MurLock is primarily used through the @MurLock() decorator.

First, you need to import the MurLockModule and set it up in your module using forRoot. This method is used for global configuration that can be reused across different parts of your application.

import { MurLockModule } from 'murlock';

@Module({
  imports: [
    MurLockModule.forRoot({
      redisOptions: { url: 'redis://localhost:6379' },
      wait: 1000,
      maxAttempts: 3,
      logLevel: 'log',
      ignoreUnlockFail: false,
    }),
  ],
})
export class AppModule {}

Then, you can use @MurLock() in your services:

import { MurLock } from 'murlock';

@Injectable()
export class AppService {
  @MurLock(5000, 'user.id')
  async someFunction(user: User): Promise<void> {
    // Some critical section that only one request should be able to execute at a time
  }
}

By default, if there is single wrapped parameter, the property of parameter can be called directly as it shown.

import { MurLock } from 'murlock';

@Injectable()
export class AppService {
  @MurLock(5000, 'userId')
  async someFunction({ userId, firstName, lastName }: { userId: string, firstName: string, lastName: string} ): Promise<void> {
    // Some critical section that only one request should be able to execute at a time
  }
}

If there are multiple wrapped parameter, you can call it by {index of parameter}.{parameter name} as it shown

import { MurLock } from 'murlock';

@Injectable()
export class AppService {
  @MurLock(5000, '0.userId', '1.transactionId')
  async someFunction({ userId, firstName, lastName }: UserDTO, { balance, transactionId }: TransactionDTO ): Promise<void> {
    // Some critical section that only one request should be able to execute at a time
  }
}

In the example above, the @MurLock() decorator will prevent someFunction() from being executed concurrently for the same user. If another request comes in for the same user before someFunction() has finished executing, it will wait up to 5000 milliseconds (5 seconds) for the lock to be released. If the lock is not released within this time, an MurLockException will be thrown.

The parameters to @MurLock() are a release time (in milliseconds), followed by any number of key parameters. The key parameters are used to create a unique key for each lock. They should be properties of the parameters of the method. In the example above, 'user.id' is used, which means the lock key will be different for each user ID.

Advanced Usage

MurLock also supports async configuration. This can be useful if your Redis configuration is not known at compile time.

import { MurLockModule } from 'murlock';

@Module({
  imports: [
    MurLockModule.forRootAsync({
      imports: [ConfigModule],
      useFactory: async (configService: ConfigService) => ({
        redisOptions: configService.get('REDIS_OPTIONS'),
        wait: configService.get('MURLOCK_WAIT'),
        maxAttempts: configService.get('MURLOCK_MAX_ATTEMPTS'),
        logLevel: configService.get('LOG_LEVEL'),
        ignoreUnlockFail: configService.get('LOG_LEVEL')
      }),
      inject: [ConfigService],
    }),
  ],
})
export class AppModule {}

In the example above, the ConfigModule and ConfigService are used to provide the configuration for MurLock asynchronously.

For more details on usage and configuration, please refer to the API documentation below.

Ignoring Unlock Failures

In some scenarios, throwing an exception when a lock cannot be released can be undesirable. For example, you might prefer to log the failure and continue without interrupting the flow of your application. To enable this behavior, set the ignoreUnlockFail option to true in your configuration:

import { MurLockModule } from 'murlock';

MurLockModule.forRoot({
  redisOptions: { url: 'redis://localhost:6379' },
  wait: 1000,
  maxAttempts: 3,
  logLevel: 'log',
  ignoreUnlockFail: true, // Unlock failures will be logged instead of throwing exceptions.
}),

Using `MurLockService` Directly

While the @MurLock() decorator provides a convenient and declarative way to handle locking within your NestJS application, there may be cases where you need more control over the lock lifecycle. For such cases, MurLockService offers a programmatic way to manage locks.

Injecting `MurLockService`

First, inject MurLockService into your service:

import { Injectable } from '@nestjs/common';
import { MurLockService } from 'murlock';

@Injectable()
export class YourService {
  constructor(private murLockService: MurLockService) {}
  
  // Your methods where you want to use the lock
}

Acquiring a Lock

You can acquire a lock by calling the acquireLock method with a unique lockKey and the desired lockTime:

async performTaskWithLock() {
  const lockKey = 'unique_lock_key';
  const lockTime = 3000; // Duration for which the lock should be held in milliseconds

  try {
    await this.murLockService.acquireLock(lockKey, lockTime);
    // Proceed with the operation that requires the lock
  } catch (error) {
    // Handle the error if the lock could not be acquired
    throw error;
  } finally {
    // Make sure to release the lock
    await this.murLockService.releaseLock(lockKey);
  }
}

Releasing a Lock

To release a lock, use the releaseLock method:

await this.murLockService.releaseLock(lockKey);

Handling Errors

Make sure to handle exceptions gracefully, especially when you are unable to acquire a lock:

try {
  // Lock acquisition attempts
} catch (error) {
  // Error handling logic
} finally {
  // Always release the lock in a finally block
}

Best Practices and Considerations

Always release locks in a finally block to avoid deadlocks.
Use meaningful lock keys that are unique to the resources they represent.
Even with ignoreUnlockFail set to true, you should implement your error handling logic. This could include logging and retry mechanisms for critical operations.
Keep lock durations as short as possible to prevent system blockage.

Directly using MurLockService gives you finer control over lock management but also increases the responsibility to ensure locks are correctly managed throughout your application's lifecycle.

This refined section is suitable for developers looking for documentation on using MurLockService directly in their projects and adheres to the typical conventions found in README files for open-source projects.

API Documentation

MurLock(releaseTime: number, ...keyParams: string[])

A method decorator to indicate that a particular method should be locked.

releaseTime: Time in milliseconds after which the lock should be automatically released.
...keyParams: Method parameters based on which the lock should be made. The format is paramName.attribute. If just paramName is provided, it will use the toString method of that parameter.

Configuration Options

redisOptions: Configuration options for the Redis client.
wait: Time (in milliseconds) to wait before retrying if a lock isn't obtained.
maxAttempts: Maximum number of attempts to obtain a lock.
logLevel: Logging level. Can be one of 'none', 'error', 'warn', 'log', or 'debug'.
ignoreUnlockFail (optional): When set to true, the library will not throw an exception if it fails to release a lock. Defaults to false to maintain backward compatibility.

MurLockService

A NestJS injectable service to interact with the locking mechanism directly.

Best Practices

Short-lived Locks: Ensure that locks are short-lived to prevent deadlocks and increase the efficiency of your application.
Error Handling: Always handle errors gracefully. If a lock isn't obtained, it's often better to return a failure or retry after some time.
Logging: Adjust the logLevel based on your environment. Use 'debug' for development and 'error' or 'warn' for production.

Limitations

Redis Persistence: Ensure that your Redis instance has RDB persistence enabled. This ensures that in case of a crash, locks are not lost.
Single Redis Instance: MurLock is not designed to work with Redis cluster mode. It's essential to ensure that locks are always set to a single instance.