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# asyncio
# `prefect.concurrency.asyncio`
## Functions
### `concurrency`
```python theme={null}
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, raise_on_lease_renewal_failure: Optional[bool] = 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.
* `raise_on_lease_renewal_failure`: Controls whether to terminate execution when lease
renewal fails. When `None` (default), follows the `strict` parameter for
backward compatibility. Set to `False` to allow long-running tasks to continue
even if a transient lease renewal error occurs. Set to `True` to terminate
execution immediately on renewal failure.
**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 theme={null}
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`
```python theme={null}
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`.
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