Object Pool

Motivation: Creating and destroying certain objects (e.g., database connections, threads) is expensive, and the application needs many short-lived instances.

Intent: Manage a pool of reusable objects, lending them out on demand and reclaiming them when no longer in use, rather than creating and destroying them repeatedly.

This is a pool of resources that can be lent out and returned when needed (connection pool, thread pool).

class ConnectionPool(private val maxSize: Int) {
    private val available = ArrayDeque<Connection>()
    private val inUse = mutableSetOf<Connection>()
 
    fun acquire(): Connection {
        val conn = if (available.isNotEmpty()) available.removeFirst()
                   else Connection()
        inUse.add(conn)
        return conn
    }
 
    fun release(conn: Connection) {
        inUse.remove(conn)
        conn.reset()
        available.addLast(conn)
    }
}