https://chenjianyong.com/tags/concurrency/ Recent content in Concurrency on Laputa Hugo en-GB Wed, 16 Jul 2025 00:00:00 +0000 https://chenjianyong.com/blog/2025/write-atomicity-in-mongodb/ Wed, 16 Jul 2025 00:00:00 +0000 https://chenjianyong.com/blog/2025/write-atomicity-in-mongodb/ <p>Recently, I’ve been building a task system with the following workflow:</p> <ol> <li>A user submits a task.</li> <li>The task is immediately stored in MongoDB.</li> <li>The task ID is returned to the user, who can poll for its status.</li> <li>A background worker periodically fetches pending tasks and executes them.</li> </ol> <p>This model is quite common when task execution can take a long time.</p> <p>However, here’s the catch: the service is deployed across multiple instances, and they may all fetch the same pending tasks from MongoDB. This creates a race condition — a task could be executed multiple times, and the final result becomes unpredictable.</p>