SIFR-ASYNC-0004: CPU-heavy function called directly from async context. - Sifr

SIFR-ASYNC-0004 belongs to the Async effect and awaitability diagnostic family. It means: cPU-heavy function called directly from async context.

Why It Happens

Sifr tracks suspension and blocking effects statically. This diagnostic fires when async code either does not really suspend, awaits work that cannot suspend, or calls blocking/CPU-heavy work without an explicit offload boundary.

Use sifr --explain SIFR-ASYNC-0004 locally to see the renderer’s exact message template and any machine-applicable suggestions for the compiler version you are running.

Erroneous Code

def crunch(values: list[int]) -> int:
    total: int = 0
    for value in values:
        total = total + value
    return total

async def main(values: list[int]) -> int:
    return crunch(values)

How To Fix It

Keep CPU-heavy work out of the async executor. Use the parallel/offload surface intended for owned CPU work.

Fixed Code

from sifr.parallel import map as par_map

def crunch(value: int) -> int:
    return value * value

async def main(values: list[int]) -> list[int]:
    return par_map(values, crunch)

Details

Field	Value
Code	`SIFR-ASYNC-0004`
Family	`ASYNC`
Severity	Error
Stability	stable
Owner	`sifr_lowering::lower::workload_annotations`
Representative fixture	`crates/sifr/tests/e2e/fail/cpu_heavy_direct_call_in_async_rejected.sifr`

See the Error Codes index for the complete catalog.