Synchronous I/O

Blocking the calling thread while I/O completes can reduce performance and affect vertical scalability.

A synchronous I/O operation blocks the calling thread while the I/O completes. The calling thread enters a wait state and is unable to perform useful work during this interval, wasting processing resources.

Common examples of I/O include:

• Retrieving or persisting data to a database or any type of persistent storage.
• Sending a request to a web service.
• Posting a message or retrieving a message from a queue.
• Writing to or reading from a local file.

This antipattern typically occurs because:

• It appears to be the most intuitive way to perform an operation.
• The application requires a response from a request.
• The application uses a library that only provides synchronous methods for I/O.
• An external library performs synchronous I/O operations internally. A single synchronous I/O call can block an entire call chain.