SIFR-ASYNC-0003: Blocking I/O function called directly from async context. - Sifr

SIFR-ASYNC-0003 belongs to the Async effect and awaitability diagnostic family. It means: blocking I/O 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-0003 locally to see the renderer’s exact message template and any machine-applicable suggestions for the compiler version you are running.

Erroneous Code

from sifr.io import read_text

async def load() -> str:
    return read_text("config.txt")

How To Fix It

Move blocking I/O behind a supported offload helper or call an async API instead of blocking the task directly.

Fixed Code

from sifr.io import read_text

@blocking_io
def read_config() -> str:
    return read_text("config.txt")

async def load() -> str:
    return await task.spawn_blocking(read_config)

Details

Field	Value
Code	`SIFR-ASYNC-0003`
Family	`ASYNC`
Severity	Error
Stability	stable
Owner	`sifr_lowering::lower::workload_annotations`
Representative fixture	`crates/sifr/tests/e2e/fail/blocking_io_direct_call_in_async_rejected.sifr`

See the Error Codes index for the complete catalog.