Detecting Blocking Tasks in Asyncio by Measuring Event Loop Latency

Asyncio's concurrency relies on cooperative multitasking, where blocking calls can freeze an entire application by preventing other tasks from progressing. This issue is often difficult to detect, as it can cause subtle delays in HTTP handlers, background jobs, and other time-sensitive operations. A solution is to implement a simple watchdog coroutine that measures event loop latency by checking how late it wakes up after a sleep command, which can signal when the loop is blocked. By exporting this latency as metrics, developers can create graphs and alerts to identify and address blocking tasks immediately. Common sources of blocking include time.sleep(), synchronous HTTP or database clients, CPU-heavy tasks, and synchronous filesystem operations. The watchdog helps correlate latency spikes with other system metrics, allowing developers to address issues by moving CPU-heavy operations to separate executors, switching to asynchronous clients, or isolating tasks into worker services.