What enables FastAPI server to process multiple requests concurrently in synchronous mode?

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FastAPI is built on top of the asynchronous web framework, Starlette, which uses asyncio, a Python library for concurrency, to handle multiple requests concurrently. Asyncio allows code to run asynchronously, meaning multiple tasks can run concurrently in a single thread, without blocking one another. This enables FastAPI to handle multiple requests concurrently in synchronous mode, without the need for threads or processes. Additionally, FastAPI uses Pydantic to efficiently serialize and deserialize data, reducing the overhead associated with input and output processing.