---
obj: concept
---
# Object Pool Pattern

## **Description:**
The Object Pool Pattern is a creational design pattern that manages a pool of reusable objects to avoid the overhead of creating and destroying objects frequently. It provides a way to efficiently manage and reuse a limited number of instances of a class, especially when creating and initializing these instances is resource-intensive.

**How it's Used:**
1. **Create a Pool**: Create a pool of objects that you want to reuse. These objects could be expensive to create, initialize, or destroy.
2. **Initialization**: Initialize the pool by creating a predefined number of objects and adding them to the pool.
3. **Object Request**: When an object is needed, instead of creating a new one, request an object from the pool.
4. **Object Return**: After using an object, return it to the pool for reuse. This is typically done by marking the object as available.
5. **Manage Pool Size (Optional)**: Implement a mechanism to ensure that the pool doesn't exceed a maximum size. If the pool is empty and an object is requested, you can decide whether to create a new object or wait until an object becomes available.

## **Example:**
Consider a scenario where you have a web server that handles incoming HTTP requests. Creating a new connection to a database for each request can be expensive. You can use the Object Pool Pattern to manage a pool of database connections efficiently:

- **Create a Pool**: Define a `DatabaseConnection` class to represent database connections.
- **Initialization**: Create and initialize a fixed number of database connections when the application starts. Add these connections to the pool.
- **Object Request**: When a new HTTP request arrives and requires a database connection, request a connection from the pool.
- **Object Return**: After handling the request, return the database connection to the pool for reuse.
- **Manage Pool Size (Optional)**: Implement mechanisms to control the pool size, such as setting a maximum number of connections or waiting for a connection to become available if the pool is empty.
    

Here's a simplified example in Java:
```java
public class DatabaseConnection {
    private boolean inUse;

    public DatabaseConnection() {
        // Initialize the database connection
        // ...
    }

    public void markInUse() {
        inUse = true;
    }

    public void markAvailable() {
        inUse = false;
    }

    public boolean isInUse() {
        return inUse;
    }
}

public class ConnectionPool {
    private List<DatabaseConnection> connections;

    public ConnectionPool(int poolSize) {
        connections = new ArrayList<>();
        for (int i = 0; i < poolSize; i++) {
            connections.add(new DatabaseConnection());
        }
    }

    public synchronized DatabaseConnection getConnection() {
        for (DatabaseConnection connection : connections) {
            if (!connection.isInUse()) {
                connection.markInUse();
                return connection;
            }
        }
        return null; // or create a new connection if allowed
    }

    public synchronized void releaseConnection(DatabaseConnection connection) {
        connection.markAvailable();
    }
}

// In your web server code
ConnectionPool pool = new ConnectionPool(10); // Initialize a pool with 10 database connections

// When handling an HTTP request
DatabaseConnection connection = pool.getConnection();
if (connection != null) {
    // Use the connection for database operations
    // ...
    // Return the connection to the pool when done
    pool.releaseConnection(connection);
}
```

By using the Object Pool Pattern, you can efficiently manage and reuse database connections, reducing the overhead of creating and destroying connections for each HTTP request. This can improve the performance and resource usage of your web server.