await condition.notify_all()

Concurrency & Async

Meaning

Wakes up all coroutines waiting on an asyncio.Condition so they can reacquire the lock and re-check shared state. Solves the lost-signal problem where some waiters might never resume if only a single notify() is issued. Reach for this when a state change is relevant to every blocked task, such as a buffer refill or a shutdown signal.

Primary Function

Concurrency control

Communicative Purpose

Notify every waiter that a condition has changed so they can resume execution.

Pattern

await condition.notify_all()

Core Structure

await ....notify_all()

Função primária

Concurrency control

Propósito comunicativo

Notify every waiter that a condition has changed so they can resume execution.

Situações de gatilho

Producer-consumer pipelines: after adding items to a shared buffer that all consumers should inspect Shutdown signaling: broadcasting a termination flag to every blocked task Barrier synchronization: releasing all participants once the last one arrives

Contextos

asyncio-based applications, producer-consumer pipelines, any code using asyncio.Condition for synchronization.

Padrão

await condition.notify_all()

Estrutura central

await ....notify_all()

Slots de substituição

condition: asyncio.Condition instance

Colocados típicos

async with condition:
await condition.wait()
condition.acquire()

Substituições comuns

condition.notify() to wake a single waiter

Erros comuns

Calling notify_all() without holding the lock → RuntimeError because the condition protocol requires the caller to own the lock Omitting await before notify_all() → returns a coroutine object that is never awaited, so no waiters are actually woken Using threading.Condition.notify_all() in async code → blocks the event loop because threading primitives are synchronous

Similar / contraste

asyncio.Lock.release() (releases a single lock) vs Condition.notify_all() (wakes all waiters); threading.Condition.notify_all() (blocking)

Interferências

Coming from Python's threading module: calling condition.notify_all() without await returns a coroutine object instead of waking waiters — asyncio.Condition.notify_all() is a coroutine that must be awaited.

Família do chunk

asyncio.Condition.wait
asyncio.Condition.notify
asyncio.Lock
asyncio.Event

Nuance

Do not use when only a subset of waiters needs to be notified; using notify_all() unnecessarily can cause excess wake‑ups and CPU overhead. Calling notify_all() while holding the lock incurs no extra lock cost, but if no waiters are present the call is a no‑op, so avoid spurious calls in tight loops. If waiters may cancel or timeout after being woken, ensure they re‑check predicates after waking to avoid acting on stale state.

Efeito pragmático

Guarantees that no waiting coroutine is missed, preventing lost signals in concurrent workflows.

Dica de memória

Wake them all: await condition.notify_all()

Nota

Must be called while holding the condition lock (async with condition). If no waiters are present, the call is a no‑op.

Upgrade path

Use asyncio.Queue or asyncio.Event for simpler one‑to‑many signaling when appropriate.

Frequência: MediumFormulaicidade: Semi-fixedTipo de construção: await <condition>.notify_all()Prioridade de aquisição: Recognition firstPrioridade de output: BothTag de espaçamento: Medium-term

Examples

import asyncio async def producer(cond: asyncio.Condition, q: list): for i in range(5): async with cond: q.append(i) print(f'produced {i}') await cond.notify_all() await asyncio.sleep(0.1) async def consumer(cond: asyncio.Condition, q: list, idx: int): while True: async with cond: while not q: await cond.wait() item = q.pop(0) print(f'consumer {idx} got {item}') await asyncio.sleep(0.2) async def main(): cond = asyncio.Condition() q: list = [] await asyncio.gather( producer(cond, q), consumer(cond, q, 1), consumer(cond, q, 2) ) asyncio.run(main())

import asyncio async def worker(cond: asyncio.Condition, wid: int): async with cond: print(f'worker {wid} waiting') await cond.wait() print(f'worker {wid} woke up') async def main(): cond = asyncio.Condition() workers = [asyncio.create_task(worker(cond, i)) for i in range(3)] await asyncio.sleep(0.5) # let workers start waiting async with cond: print('broadcasting') await cond.notify_all() await asyncio.gather(*workers) asyncio.run(main())

import asyncio class AsyncBarrier: def __init__(self, parties: int): self.parties = parties self.count = parties self.cond = asyncio.Condition() async def wait(self): async with self.cond: self.count -= 1 if self.count == 0: self.count = self.parties await self.cond.notify_all() else: await self.cond.wait() async def task(barrier: AsyncBarrier, id: int): print(f'Task {id} before barrier') await barrier.wait() print(f'Task {id} after barrier') async def main(): barrier = AsyncBarrier(3) await asyncio.gather(*[task(barrier, i) for i in range(3)]) asyncio.run(main())