---
title: asyncio
sidebarTitle: asyncio
---

# `prefect.concurrency.asyncio`

## Functions

### `concurrency` <sup><a href="https://github.com/PrefectHQ/prefect/blob/main/src/prefect/concurrency/asyncio.py#L24" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>

```python
concurrency(names: Union[str, list[str]], occupy: int = 1, timeout_seconds: Optional[float] = None, max_retries: Optional[int] = None, lease_duration: float = 300, strict: bool = False, holder: 'Optional[ConcurrencyLeaseHolder]' = None) -> AsyncGenerator[None, None]
```


A
context manager that acquires and releases concurrency slots from the
given concurrency limits.

**Args:**
- `names`: The names of the concurrency limits to acquire slots from.
- `occupy`: The number of slots to acquire and hold from each limit.
- `timeout_seconds`: The number of seconds to wait for the slots to be acquired before
raising a `TimeoutError`. A timeout of `None` will wait indefinitely.
- `max_retries`: The maximum number of retries to acquire the concurrency slots.
- `lease_duration`: The duration of the lease for the acquired slots in seconds.
- `strict`: A boolean specifying whether to raise an error if the concurrency limit does not exist.
Defaults to `False`.
- `holder`: A dictionary containing information about the holder of the concurrency slots.
Typically includes 'type' and 'id' keys.

**Raises:**
- `TimeoutError`: If the slots are not acquired within the given timeout.
- `ConcurrencySlotAcquisitionError`: If the concurrency limit does not exist and `strict` is `True`.

Example:
A simple example of using the async `concurrency` context manager:
```python
from prefect.concurrency.asyncio import concurrency

async def resource_heavy():
    async with concurrency("test", occupy=1):
        print("Resource heavy task")

async def main():
    await resource_heavy()
```


### `rate_limit` <sup><a href="https://github.com/PrefectHQ/prefect/blob/main/src/prefect/concurrency/asyncio.py#L79" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>

```python
rate_limit(names: Union[str, list[str]], occupy: int = 1, timeout_seconds: Optional[float] = None, strict: bool = False) -> None
```


Block execution until an `occupy` number of slots of the concurrency
limits given in `names` are acquired.

Requires that all given concurrency limits have a slot decay.

**Args:**
- `names`: The names of the concurrency limits to acquire slots from.
- `occupy`: The number of slots to acquire and hold from each limit.
- `timeout_seconds`: The number of seconds to wait for the slots to be acquired before
raising a `TimeoutError`. A timeout of `None` will wait indefinitely.
- `strict`: A boolean specifying whether to raise an error if the concurrency limit does not exist.
Defaults to `False`.

**Raises:**
- `TimeoutError`: If the slots are not acquired within the given timeout.
- `ConcurrencySlotAcquisitionError`: If the concurrency limit does not exist and `strict` is `True`.

