Ownership Across Tasks

Concurrency boundaries are ownership boundaries. A spawned task may outlive the current line of code, so values captured by that task must be owned and safe to send.

Owned Inputs

Pass owned values into spawned tasks.

async def count_items(own items: list[int]) -> int:
    await task.sleep(0.0)
    return len(items)

async def main() -> Result[None, ScopeFailure]:
    async with task.scope() as scope:
        handle = scope.spawn(count_items([1, 2, 3]))
        result = await handle
    return None

The child owns its input. The parent observes the task through the handle.

Shared Read Access

Use explicit synchronization primitives for values shared across tasks.

from sifr.sync import Shared

async def read_shared(own shared: Shared[int]) -> int:
    await task.sleep(0.0)
    return shared.get()

Shared[T] is for concurrent read access. Mutable shared state uses explicit lock types from sifr.sync.

Mutable Borrows And Await

Mutable borrows must end before an await. This shape is rejected because the mutable borrow remains live when the function reaches await:

async def rejected(mut items: list[int]) -> None:
    items.append(1)
    await task.sleep(0.0)

End the mutation before awaiting by moving the mutation into a synchronous helper.

def append_before_await(mut items: list[int]) -> None:
    items.append(2)
    return None

async def main() -> Result[None, ScopeFailure]:
    values: list[int] = [1]
    append_before_await(values)
    await task.sleep(0.0)
    return None

Lock guards, borrowed references, and mutable borrows cannot cross task or await boundaries. Move owned values, clone when copying is intended, or use sifr.sync primitives.

Next Steps

Parallel Work

Apply the same ownership rules to CPU worker boundaries.

Ownership and Mutability

Review mut, own, own mut, and borrowed-value escape rules.

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Ownership Across Tasks

Owned Inputs

Shared Read Access

Mutable Borrows And Await

Next Steps

Parallel Work

Ownership and Mutability

​Owned Inputs

​Shared Read Access

​Mutable Borrows And Await

​Next Steps

Parallel Work

Ownership and Mutability

Owned Inputs

Shared Read Access

Mutable Borrows And Await

Next Steps