##### Question Design and implement a thread-safe, lazily initialized ConnectionPool: classes ConnectionPool and PooledConnection with __init__, getConnection, close. Only create Connection on getConnection when no idle exists; reuse idle connections; cap active connections at maxConnectionNum.

This question evaluates understanding of concurrent resource management, thread-safety, lazy initialization, connection pooling semantics, and lifecycle handling in a multi-threaded Python environment.

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Design a lazy ConnectionPool | Airtable Interview Question

Thread-Safe, Lazily Initialized Connection Pool

Context

You need to design a thread-safe connection pool in Python that lazily creates connections and reuses them. The pool should cap the number of total connections and block callers when no connections are available. A PooledConnection wrapper should ensure that calling close returns the connection to the pool instead of closing the underlying connection.

Assumptions:

Language: Python, multi-threaded environment.
A connection factory (callable) can be provided to create new underlying connections. For demonstration, a simple stub Connection is used.

Requirements

Implement the following classes and methods:

ConnectionPool

init (maxConnectionNum, connection_factory=None)
getConnection(timeout=None)
close()

PooledConnection

init (pool, raw_connection)
close()

Behavioral constraints:

Lazy initialization: do not create connections in init .
Reuse idle connections when available.
Create a new connection on getConnection only if there are no idle connections and the total created is below maxConnectionNum.
Cap total connections at maxConnectionNum. When the cap is reached and no idle connections exist, getConnection should block (optionally with timeout) until one is returned.
PooledConnection.close returns the connection to the pool (idempotent); it should not close the underlying connection unless the pool is closed.
Pool close() closes idle connections immediately, marks the pool as closed, and causes future getConnection calls to fail. Connections returned after close should be closed rather than re-pooled.

Context

Assumptions:

Language: Python, multi-threaded environment.

A connection factory (callable) can be provided to create new underlying connections. For demonstration, a simple stub Connection is used.

Requirements

Implement the following classes and methods:

ConnectionPool

init (maxConnectionNum, connection_factory=None)

getConnection(timeout=None)

close()

PooledConnection

init (pool, raw_connection)

close()

Behavioral constraints:

Lazy initialization: do not create connections in init .

Reuse idle connections when available.

Create a new connection on getConnection only if there are no idle connections and the total created is below maxConnectionNum.

Cap total connections at maxConnectionNum. When the cap is reached and no idle connections exist, getConnection should block (optionally with timeout) until one is returned.

PooledConnection.close returns the connection to the pool (idempotent); it should not close the underlying connection unless the pool is closed.

Pool close() closes idle connections immediately, marks the pool as closed, and causes future getConnection calls to fail. Connections returned after close should be closed rather than re-pooled.

Design a lazy ConnectionPool

Quick Overview

Thread-Safe, Lazily Initialized Connection Pool

Context

Requirements

Solution

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Design a lazy ConnectionPool

Quick Overview

Thread-Safe, Lazily Initialized Connection Pool

Context

Requirements

Solution

Comments (0)