JAVA Developer Guide to start with Object Pool Design Pattern
Imagine a public swimming pool where people come to swim and have fun. This swimming pool has a limited number of swim tubes, which are high in demand.
To manage the swim tubes effectively, the swimming pool manager has decided to follow the Object Pool design pattern. The manager has created a pool of swim tubes and whenever a swimmer requests for a swim tube, the manager gives them one from the pool. The swimmer uses it for a limited time and returns it back to the pool.
Now, if there are no swim tubes available in the pool, the swimmer has to wait for one to be returned. The manager makes sure that the returned swim tubes are cleaned and made available for use again. This helps the manager efficiently manage the swim tubes and provide a better experience to the swimmers.
In this scenario, the swim tubes are the objects and the pool of swim tubes is the object pool. The swimming pool manager is the object pool manager and the swimmers are the clients.
What is Object Pool Design Pattern?
The Object Pool Pattern is one of the creational design patterns from the book “Design Patterns: Elements of Reusable Object-Oriented Software”. The pattern is used in software development to manage the reuse of objects that are expensive to create.
The pattern is implemented as a container object that holds a pool of objects that are ready to be used. The container object provides an interface for client code to request an object from the pool. When a client requests an object, the container returns an object from the pool if one is available.
If no objects are available, the container creates a new object, adds it to the pool, and returns it to the client, or it can ask the client to wait until an object is released by another client and available back in the pool.
The main benefit of the Object Pool design pattern is to improve the performance of an application by reducing the time it takes to create new objects and the memory overhead associated with object creation. The pattern also provides a way to manage the number of objects created, reducing the risk of resource exhaustion and improving the application’s stability.
This pattern can be useful in a variety of situations, such as database connections, network sockets, and thread pools. By using an object pool, an application can avoid the overhead of creating and destroying objects, making it more efficient and scalable.
Object Pool Pattern JAVA Example
Let’s say you are building a web application that needs to send email marketing notifications to users. You decide to use a third-party email service provider to handle the sending of emails.
However, you notice that sending emails can be a slow and resource-intensive process. You don’t want to overload the third-party service with too many requests as you want to use the service within the free tier limit usage (limited connection at a time), but you also don’t want to make users wait too long for their email notifications to be sent.
To solve this problem, you decide to use the object pool design pattern to manage a pool of email client objects. Each email client object represents a connection to the third-party email service provider.
When the application needs to send an email, it retrieves an email client object from the pool. If all email clients are in use, the application waits until one becomes available. Once an email client is available, the application uses it to send the email notification. After the email is sent, the email client is returned to the pool for future use.
This approach allows the application to send email notifications without overloading the third-party service with too many requests at once. By managing a pool of email clients, the application can reuse existing connections instead of creating new ones for every email, which saves resources and reduces the overall load and usage limit on the third-party service.
Object Class Definition
In this example, created EmailClient class which we will be using in the pooling manager
Pool Manager Definition
In this example, the EmailClientPoolManager class is having fixed pool size and a Queue as pool for storing EmailClient objects in FIFO manner.
The borrowClient method removes an object from the pool and returns it. If the pool is empty, the method blocks until an object is available.
The returnClient method accepts an object and adds back to the pool
Client Class Definition
Created EmailSender class which calls pool manager’s borrowClient to get one EmailClient object, utilize it based on requirements, and finally return back to pool manager.
Object Pool Pattern in Action
Created a Demo class that will create multiple EmailSender objects and will wait till execution is over.
Key Points in the Implementation
- Object Creation: If we need the objects on demand then we can choose lazy initialization, or if object creation is expensive and take time then we can go with eager initialization where we create objects at the time of application startup. While implementing a method to create objects, we need to make sure that it is stored in the pool for later use.
- Object Reuse: To provide a mechanism to reuse objects from the pool instead of creating new ones.
- Object Management: Need to maintain a pool of objects and keep track of which objects are in use and which are available for reuse. The data structure of the pool varies based on the requirements.
- Pool Size: Determine the maximum size of the object pool and limit the number of objects that can be created. This helps to prevent resource exhaustion and improve performance.
- Object Lifetime: It’s a good practice to define the lifetime of objects in the pool and remove or replace them as needed.
- Object Validation: We should implement a mechanism to validate objects in the pool before they are reused. This helps to ensure that the objects are in a suitable state for reuse.
- Synchronization: Ensure thread safety when multiple threads access the object pool concurrently. This can be achieved through the use of synchronized methods or locks.
- Exception Handling: Handle exceptions that might occur during the creation, reuse, or validation of objects in the pool.
- Performance Optimization: Optimize the performance of the object pool by reducing the overhead of object creation and management.
- Object Pool Manager: Object pool manager should be implemented as a Singleton design pattern to have a single global pool of resources across the application.
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