FastAPI jassuporta kemm async def kif ukoll regular def għal path operations. Il-għażla hija importanti għall-performance: uża async def meta tista' non-blocking I/O, u regular meta l-kodiċi tiegħek sejjaħ operazzjonijiet blocking (sinkrini).
awaitdef@app.get("/async")
async def async_endpoint():
data = await fetch_from_api() # await non-blocking I/O — efficient
return data
@app.get("/sync")
def sync_endpoint():
data = blocking_db_call() # ordinary blocking code
return data
async def → runs on the main event loop. Efficient ONLY if you await non-blocking calls.
⚠️ A BLOCKING call inside async def blocks the WHOLE event loop → kills concurrency!
def → FastAPI runs it in a THREAD POOL, so blocking code doesn't block the event loop.
Safe for synchronous/blocking libraries.
# ✅ async def — when you can await async libraries (httpx, async DB drivers)
async def get_user():
async with httpx.AsyncClient() as c:
return await c.get(url)
# ✅ plain def — when using SYNCHRONOUS/blocking libraries (requests, sync ORM)
def get_user():
return requests.get(url).json() # blocking → FastAPI runs it in a thread
# ❌ THE DANGEROUS MISTAKE — blocking call inside async def
async def bad():
return requests.get(url).json() # blocks the event loop! Use `def` or an async client
Ir-regola kritika: qatt tpoġġi blocking calls f'async def — imbagħad iblokka l-event loop u tiddistroġi l-concurrency. Jew uża librerija async b'await, jew uża plain def (li FastAPI jwaqqaha b-mod sikur f'thread pool).
Il-għażla korretta bejn async def u def taffettwa direttament il-performance u l-concurrency tal-API tiegħek, u meta tagħmel ħażin huwa żball komuni u serjuż.
L-insight ewlenija huwa li async def huwa benefiku biss meta await operazzjonijiet non-blocking — poġġi blocking call (bħall-librerija sinkrinja requests jew database driver li jblokka) ġewwa async def u imbagħad iblokka l-event loop kollu, ifriża l-request konkorrenti kollha u tappunta l-għan tal-async.
Viceversa, FastAPI b'ċirkostanza ċkejkna jwaqqaq plain def endpoints f'thread pool, għalhekk il-kodiċi sinkrinu/blocking huwa sigur hemmhekk.
L-għarfien ta' din ir-regola — uża async def b'libreriji verament async, uża plain def għal kodiċi li jblokka, u qatt tħallat blocking calls ġewwa async def — huwa essenzjali biex tikteb endpoints FastAPI performanti u tevi ż-żball sottili imma devastanti li tkun accidenti tisserijjalizza l-request kollha wara event loop miblokka.