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Deconstruct the Python FastAPI backend engine from raw Uvicorn ASGI socket loops to Rust-compiled Pydantic V2 serialization and hierarchical Dependency Injection DAGs.
How asynchronous cooperative multitasking handles 50,000+ simultaneous connections with zero thread exhaustion.
Every concurrent HTTP request locks an entire OS thread. If 100 requests wait for slow database queries, all 100 worker threads freeze, rejecting incoming traffic with HTTP 504 Gateway Timeouts.
Single-thread event loop using cooperative coroutines. When a request awaits I/O (database, external API), the loop immediately processes hundreds of other requests without blocking.
Why traditional WSGI synchronous servers block threads, and how ASGI enables non-blocking async Python I/O.
How FastAPI automatically routes standard "def" functions to external AnyIO thread pools to avoid blocking the main event loop.
The 20x speedup of Pydantic V2 using pydantic-core in Rust, strict type coercion, and JSON schema extraction.
How FastAPI builds a Directed Acyclic Graph (DAG) of Depends(), memoizes sub-dependencies, and executes teardown cleanup.
Streaming real-time SSE tokens, full-duplex WebSockets, and firing background tasks after sending HTTP responses.